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Although the species holds no special status, there are several threats facing the woodpecker. Many of these threats stem from habitat loss and degradation. Overgrazing, poor regeneration of oaks in California, and destruction of oak and pine forests for firewood or development are among the biggest threats facing the species.
IUCN Red List of Threatened Species: least concern
The Acorn Woodpecker is often considered a pest by nut and fruit farmers when the bird feeds on their crops.
Native Americans in California used Acorn Woodpeckers for food and collected their feathers for ornamentation on garments.
The main diet of the Acorn Woodpecker consists of insects, sap, oak catkins, fruit, and flower nectar. Acorns are critical for winter survival. Occassionally, it eats grass seeds, lizards and bird eggs. The bird prefers, however, flying ants and other Hymenoptera and Coleoptera. When foraging, the woodpecker often sits at the tops of trees while flycatching. Most foraging, however, is performed in or near the canopy. The woodpecker rarely goes to the ground except to pick up grit and fallen acorns. Usually, acorns are removed singly from trees, but the bird may also break off a twig holding up to three acorns. Sapsucking is a communal affair and group members congregate at a set of holes that are used repeatedly for several years.
The Acorn Woodpecker stores insects in cracks or crevices and nuts in indiviually-drilled holes in graneries. A granary tree may hold as many 50,000 holes. Holes are usually drilled in dead limbs and in thick bark during the winter. Any dead or living tree with deep dry bark can used as granary. Studies have shown that these granaries are so important that they are one of the main reasons why acorn woodpeckers live in such large families, at least in California. Only a large group can collect so many acorns and also defend them against other groups.
The Acorn Woodpecker is found from northwestern Oregon, California, the American Southwest, and western Mexico through the Central American highlands and into the northern Andes of Colombia.
Biogeographic Regions: nearctic (Native ); neotropical (Native )
The Acorn Woodpecker prefers pine-oak woodlands where oak trees are plentiful. They are also found in riparian corridors, and in Douglas firs, redwood and tropical hardwood forests as long as oaks are available nearby. Urban parks and suburban areas that possess numerous oak trees are often also home to the species.
Terrestrial Biomes: forest ; rainforest
Average lifespan
Status: wild: 114 months.
Perception Channels: visual ; tactile ; acoustic ; chemical
The Acorn Woodpecker is a medium-sized, black and white clown-faced bird with a red crown, glossy black and white head, white eyes, and white rump and wing patches. There is usually at least one red or yellow tipped feather on the throat. In Colombian populations, the male has a solid red crown while the female has a black band separating the red crown from the white forehead. The wing span of the woodpecker ranges between 13-15 centimeters.
Other Physical Features: endothermic ; bilateral symmetry
Average mass: 73 g.
Average basal metabolic rate: 0.737 W.
Mating systems of Acorn Woodpeckers range from monogamy in some populations to cooperative polygyny. Generally, Acorn Woodpecker groups contain 1-7 male breeders that compete for matings with 1-3 egg-laying females. In groups that contain more than one female breeder, the female cobreeders lay their eggs in the same nest cavity. There is often extreme reproductive competition between joint-nesting females, who regularly destroy eggs laid by their cobreeders. After females have established a normal laying sequence, egg destruction stops. Reproduction competition between males is displayed by attempts by a male to disrupt copulation between another pair. Courtship and pair-bonding displays are absent.
Nest cavities are drilled into large dead or living limbs in trees or snags, which may contain granaries. The inside of the nest cavity is lined with fresh wood chips, and nest holes may be used repeatedly for several seasons. Average clutch size for a group with more than one female is five white, elliptical eggs. The average clutch size for a singleton female is four eggs. Eggs are laid at approximately 24 hour intervals. The incubation period is 11 days and both male and female breeders incubate. Once the chicks have hatched, all group members participate in providing food. Nestlings leave the nest after 30-32 days.
Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Average time to hatching: 14 days.
Average eggs per season: 4.
In general, acorn woodpeckers occupy valley and foothill oak (Quercus spp.) woodlands [17,30,61,82,155], oak-pine (Pinus spp.) woodlands [7,78,82,89,90,93,95,118,121,128,145], and oak savannas [5,45,61,72,78,132,155]. Other plant communities occupied by the acorn woodpecker include mixed-evergreen forest [72,91], chaparral, savanna-grasslands [72], riparian woodlands [72,134], coast redwood (Sequoia sempervirens) forest adjacent to oak woodlands [97], Arizona canyon riparian forest, Arizona Madrean foothill forest, and Mexican Madrean foothill forest [78]. Acorn woodpeckers may be common in urban areas where oaks are present [76].
Populations of acorn woodpeckers in Washington, Oregon, and California occupy plant communities dominated by Oregon white oak (Quercus garryana) and California black oak (Q. kelloggii); blue oak (Q. douglasii) and California black oak (Q. kelloggii) [149,152,155]; coast live oak (Q. agrifolia), valley oak (Q. lobata), and California black oak [45,90]; and tanoak (Lithocarpus densiflorus) [34]. In south-central Washington, Oregon white oak may be mixed with Douglas-fir (Pseudotsuga menziesii) or ponderosa pine (Pinus ponderosa) [93]. On the Santa Rosa Plateau Reserve in Riverside County, California, acorn woodpeckers occupy habitat dominated by Engelmann oak (Q. engelmannii) and coast live oak [53]. On the east side of the Sierra Nevada, acorn woodpeckers occupy habitat dominated by California black oak and Jeffrey pine (P. jeffreyi) [64].
At Hastings Natural History Reservation, in Monterey County, California, acorn woodpeckers occupy foothill woodlands, savanna-grasslands, riparian woodlands, chaparral, and mixed-evergreen forest. Dominant tree species in foothill woodlands at Hastings Reservation include blue oak and valley oak. Dominant trees in savanna-grasslands at Hastings Reservation include valley oak, blue oak, and coast live oak. Dominants in riparian woodlands include willow (Salix spp.), California sycamore (Platanus racemosa), coast live oak, and valley oak. Chaparral habitat is dominated by chamise (Adenostoma fasciculatum) and wedgeleaf ceanothus (Ceanothus cuneatus), and mixed evergreen forest is dominated by coast live oak and California black oak [72,91].
Acorn woodpecker populations in the southwestern United States occupy primarily low-elevation montane plant communities dominated by Gambel oak (Q. gambelii) and ponderosa pine [20,20,29,49,65,101,123,124,143,145]. They also inhabit the following Arizona canyon riparian forest, dominated by Arizona sycamore (Platanus wrightii), Arizona walnut (Juglans major), and Arizona cypress (Crataegus douglasii); Arizona Madrean foothill forest, dominated by Mexican pinyon (P. cembroides), alligator juniper (Juniperus deppeana), silverleaf oak (Q. hypoleucoides), and Arizona white oak (Q. arizonica); and Mexican Madrean foothill forest, dominated by Mexican pinyon, drooping juniper (Juniperus flaccida), gray oak (Q. grisea), and Texas madrone (Arbutus xalapensis) [78].
The acorn woodpecker is omnivorous. Tree sap, insects (Hymenoptera and Coleoptera), and green and mature acorns comprise most of their diet [22,66,72,76,78,90,91,95,122,147]. For a list of insects eaten by the acorn woodpecker, see Koenig and Mumme [72]. Other foods consumed include pinyon pine seeds [91,133], Jeffrey pine seeds [120], oak buds and catkins [72], grass seeds [76], and occasionally lizards, bird eggs [90], and bats [92]. Olives (Oleo europaea) [96], cultivated nuts [53,91,96,133], corn (Zea mays), figs (Ficus carica), and wheat (Triticum aestivum) may also be eaten [96]. Grit is collected from the ground (usually road beds) several times a day and ingested [91].
Foraging techniques include sapsucking, flycatching, and acorn storage, depending on time of year [22,72,89,90,122]. Sapsucking by acorn woodpeckers in California occurs from February to early March, and June to August [72,91]. During winter at Hastings Reservation, sap is extracted from the middle and upper canopies of valley oak and blue oak. During spring, acorn woodpeckers extract sap from California black oak and live oak. During June and July, sap is extracted from live oak [72,89,90,91]. Bast, which is the phloem/cambium removed from the inner bark of trees, may be eaten during winter [122]. Sap holes are reused every year, and new holes are continually added [91]. At Hastings Reservation, flycatching is the primary foraging method during the nesting period in April and May. Insects may also be consumed on warm winter days. Acorn woodpeckers do not usually glean insects from tree bark or drill for wood-boring insects, but flycatch from stumps, uppermost tree branches, or branches just above the grass [72,89,90,91,122]. Insects are the main food item fed to nestlings, and are either fed directly to nestlings or temporarily stored under loose bark or in tree crevices [72,89,90,91,122].
Acorn woodpeckers are "larder hoarders" and store acorns in granaries [69] (see Granaries). They are also considered "opters", either storing food or migrating depending on food availability [122]. In California, acorns comprise >50% of the acorn woodpecker diet [83], and in Arizona and New Mexico, acorns comprise 25% to 50% of the acorn woodpecker diet [95]. From late summer to fall, green acorns are eaten directly from trees. At Hastings Reservation, acorn woodpeckers ate green acorns directly from California black oak, valley oak, blue oak, coast live oak, and canyon live oak [72,90,91]. From September to December, acorns are stored in granaries for later use [72]. Stored acorns are usually edible for only 1 year [69]. Acorn woodpeckers are most dependent on stored acorns from September to March, and may use stored acorns through spring and summer if they are available [66,89,90,91]. Use of acorns during the remainder of the year depends on availability of other foods [91] and whether or not the granary is depleted due to a poor acorn crop [90]. Acorns are the main food stored, but cultivated nuts, pinyon pine seeds, and gray pine seeds may also be stored [69,91,122,133]. Acorn woodpeckers in California may be able to survive winters without stored acorns, depending on availability of other foods [122].
Acorns are gathered by all group members for 4 to 6 weeks and stored in 1 or 2 granaries. Acorn woodpeckers prefer storing acorns in conifers due to softer bark. Storage holes are usually 0.5 inches (1.3 cm) in diameter and 1.5 inches (3.8 cm) deep. Acorns are inserted with the base facing outward and are pounded into place. As acorns dry and shrink, they must be moved to smaller holes [69,72,89]. Re-storage of acorns usually occurs for at least 6 weeks after harvest. Storage hole construction is an ongoing activity performed by all acorn woodpeckers in a group [89].
Due to low protein and high tannin content, acorns are a relatively poor food resource for acorn woodpeckers. Available carbohydrates and protein vary little among oak species, but lipid content varies widely and is highest in coast live oak and California black oak. Some species of oak, such as coast live oak and California black oak, contain high amounts of tannins, which reduce nutritional food value by binding protein. Despite high tannin levels, coast live oak and California black oak acorns provide the largest energetic content for acorn woodpeckers. The following table shows composition and energetic content of the acorns most commonly eaten by acorn woodpeckers at Hastings Reservation [72]:
Composition and energetic content of acorns eaten by acorn woodpeckers in Monterey County, California [72] Oak species Soluble tannins (%) Lipids (%) Protein (%) Total available carbohydrates (%) Energetic content (kJ/gm) Valley oak 0.373 5.6 5.5 13.6 5.53 Blue oak 0.384 8.3 6.6 17.4 7.49 Canyon live oak 0.398 16.7 3.9 12.6 11.39 Coast live oak 0.460 24.3 7.1 13.2 13.23 California black oak 0.444 26.5 5.3 14.9 14.07At Hastings Reservation, acorn woodpeckers stored a mixture of species of acorns, and selection of different acorn species for storage was unrelated to energetic value. Valley oak acorns were stored by acorn woodpeckers much more frequently, blue oak acorns were stored much less frequently, and coast live oak acorns were stored in roughly the same frequency as the estimated relative abundance of the trees and the estimated relative productivity of the species. The study was conducted during a year when crops of valley oak, blue oak, and coast live oak were excellent, to ensure that acorns of any of the 3 species were abundant enough to be stored in granaries. Acorn woodpeckers also preferred to store acorns that were smaller than those most available and did not discriminate based on insect parasitism [69].
Acorn woodpeckers store a small amount of acorns considering their energetic needs [69,72]. For example, At Hastings Reservation, 120 to 130 acorn woodpeckers stored an average of 344 acorns/bird each year. This accounted for only 6% to 7% of total yearly metabolic requirements [66]. Acorn storage is apparently unrelated to group size [72].
Acorn production varies widely from year to year, species to species, and tree to tree. In California oak woodlands, 120 to 130 acorn woodpeckers collected acorns from 5 oak species. The relative proportion of the total of each species varied considerably from year to year but the total number collected was relatively constant, ranging between 42,000 and 45,000 acorns. The following table shows yearly variation in species composition of acorns stored by acorn woodpeckers [66]:
Yearly variation in species composition of acorns stored by acorn woodpeckers at Hastings Reservation [66]Years
Percent of total stored acorns by species
Total (n) coast live oak valley oak blue oak California black oak canyon live oak 1975-1976 5.0 17.0 51.4 18.1 8.4 45,470 1976-1977 27.1 34.3 15.6 15.2 7.9 41,927 1977-1978 19.5 50.3 21.6 8.0 0.6 43,425 Mean 16.9 33.7 30.0 13.8 5.6 43,607For more information on acorn woodpecker foraging methods and habits in Yolo County, California, see Roberts [122].
Defense of resources: Interspecific and intraspecific aggression within a territory is common in acorn woodpeckers [59,91,122]. Granaries are the main resource defended; however, roost and nest cavities, sap trees, and hawking perches are also defended [59,89,91,122]. Acorn woodpeckers defend resources from the following mammals and birds: eastern fox squirrel (Sciurus niger) [90], California ground squirrel (Spermophilus beecheyi) [72], white-breasted nuthatch (Sitta carolinensis), Steller's jay (Cyanocitta stelleri), oak titmouse (Baeolophus inornatus), northern flicker (Colaptes auratus), western scrub-jay (Aphelocoma californica), spotted towhee (Pipilo maculatus), Nuttall's woodpecker (Picoides nuttallii), European starling (Sturnus vulgaris), ruby-crowned kinglet (Regulus calendula) [90], yellow-billed magpie (Pica nuttalli), and American crow (Corvus brachyrhynchos) [72].
Adult acorn woodpeckers sometimes defend primary granary trees from juvenile birds, forcing younger birds to store acorns in secondary granaries until they reach adulthood [91].
Population trends: Yearly acorn yields [72,75,91] and number of oak species in an area [19,121] may influence population dynamics of acorn woodpeckers. Acorn woodpecker populations are typically larger in areas containing >3 oak species, due to asynchrony in acorn production [19,121] (see Stand composition/structure). Acorn crop failures may lead to "precipitous" declines in acorn woodpecker populations, and may occur every 4 to 5 years [75].
According to Breeding Bird Surveys conducted in western North America from 1968 to 1991, acorn woodpecker populations increased 0.9% (n=137 survey routes) [54,108,109]. However, in the Sierra Nevada, acorn woodpecker populations decreased 5.3% per year from 1966 to 1996 [131]. Additionally, as of 1997, acorn woodpecker populations were decreasing on Breeding Bird Survey routes in managed ponderosa pine habitat in Arizona and New Mexico [49].
In general, birds are usually favored by successional diversity and new growth of food and shelter following fire [157]. The ability of birds to occupy a site after fire depends on pre- and postfire management activities such as logging. Snag-nesting species typically increase following fire and are influenced by postfire snag availability [48].
Acorn woodpeckers are adapted to habitat with recurring fires of varying severity [39,105,142], which create a mosaic of habitat types [111,112,157]. Acorn woodpecker abundance appears to increase several years following fire [18,62], probably due to an increase in acorn production [62]. Following fire in ponderosa pine habitat, acorn woodpecker use may increase in response to increases in insect populations [88].
Prior to European settlement in lowlands and foothills of the Pacific Northwest, wildfires were low-to moderate-severity, with short fire-return intervals [1,58,63,85,148]. Frequent, low-severity fires maintained acorn woodpecker habitat by reducing conifers and grasses, initiating sprouting of oaks, reducing fuel loads, and preventing loss of mature oak trees [1,16,52,85,86,101]. Fire exclusion became policy in the Pacific Northwest in the early 1900s [1], resulting in longer fire-return intervals in lowlands and foothills [58]. Without fire, open-canopy oak savannas become dense oak woodlands, and eventually, conifer forests [1,52]. Consequently, bird species composition has been affected by the encroachment of conifers and nonnative shrubs [43,47,151].
In oak-pine woodlands and ponderosa pine forests in the southwestern United States, low- to moderate-severity wildfires occurred at about 1 fire/decade prior to European settlement [4,36,39,142]. These frequently-occurring fires thinned smaller trees, reduced surface fuel, and invigorated understory vegetation [4,36,136]. According to Pyne [113] and Moir and others [101], low-severity fire is one of the most important natural disturbances in southwestern ponderosa pine forests.
Response to fire varies in oaks. Oregon white oak, California black oak, valley oak, coast live oak, and Gambel oak are fire-resistant species, surviving low- to moderate-severity fires [1,3,37,43,44,100,110,137,140,141]. Therefore, acorn woodpeckers in habitat dominated by these species are probably negatively impacted only by severe fire. After high-severity fire, oaks may be completely killed and some may not produce acorns for decades [26,107]. Blue oak is less insulated against fire than other oaks due to thin bark, which tends to flake off as the tree ages [150]. Mature blue oak is resistant to top-kill by low-severity surface fires and most moderate-severity surface fires, but is top-killed or killed by severe fires or the sustained heat of most chaparral fires [99,110]. Interior live oak is sensitive to fire [110] but readily resprouts [14]. For more information about fire and oaks used by the acorn woodpecker, see the FEIS reviews on oak species (Oregon white oak, California black oak, valley oak, coast live oak, Gambel oak, blue oak, and interior live oak).
Data on acorn woodpecker response to wildfire are sparse. In 3 studies in the southwestern United States, acorn woodpeckers were not detected in unburned habitats, but were detected at least 2 years following wildfire [18,62]. Three and 4 years following the Horseshoe and Hockderffer wildfires in the Coconino National Forest, Arizona, acorn woodpeckers were detected only during the breeding season and only in severely burned areas. Habitat was dominated by ponderosa pine. Details about the wildfire, such as size and severity, were not given [18]:
In the Prescott National Forest, Arizona, acorn woodpeckers were not detected following wildfire in either unlogged or logged burned areas during postfire years 1 and 2. They were detected, however, during spring and fall in an unburned, 5-year-old clearcut. The wildfire burned a total of 29,650 acres (12,000 ha). Within the burn perimeter, there were 11,860 acres (4,800 ha) of ponderosa pine. One-half of the 11,860 acres of the ponderosa pine forest was completely killed. Within the burned area, uncut, partially cut, and clearcut sites were examined during postfire years 1 and 2. Three unburned sites were selected that most closely matched the burned sites with respect to logging. Overall, shrub live oak (Q. turbinella) and Gambel oak were more abundant on burned sites. In the unburned, 5-year-old clearcut site where acorn woodpeckers were found, shrub diversity was greater compared to burned sites. Gambel oak was present in the clearcut, and density of Gambel oak slightly surpassed density of ponderosa pine [15].
Acorn woodpeckers were detected 4 years after the La Mesa Wildfire in Bandelier National Monument, New Mexico. Prior to the fire, acorn woodpeckers were not detected in bird surveys. They were first detected on burned transects in postfire year 6, and detections increased by postfire year 14. Three transects (Apache, Escobas, and Burnt) were located in burned areas of mixed-conifer, ponderosa pine-mixed-conifer, and ponderosa pine/pinyon-juniper habitats. One transect (Frijoles) was located in unburned pinyon-juniper habitat. On the 3 burned transects, vegetation was killed by crown fire or scorching on 25% to 80% of the area. No postfire logging occurred. Bird surveys were conducted 1 breeding season before the fire and in postfire years 1, 2, 4, 6, and 14. In this habitat, acorn production resumed 4 years after fire, favoring acorn woodpeckers. The following table shows the number of detections of acorn woodpeckers before and after the wildfire [62]:
Number of detections of acorn woodpeckers/40-ha transects (SE) before and after the La Mesa Wildfire, Bandelier National Monument, New Mexico [62] Transect name Percentage of area burned by high-severity fire Prefire year 1 Postfire year 1 Postfire year 2 Postfire year 4 Postfire year 6 Postfire year 14 Apache 25 0 0 0 0 0 0 Escobas 33 0 0 0 0 2 (1) 13 (3) Burnt 80 0 0 0 0 4 (2) 4 (1) Frijoles (unburned) 0 0 0 0.3 (0.3) 0 0 0In the San Dimas Experimental Forest, California, acorn woodpeckers were occasionally detected in burned grassland (grass species not specified) at 3,000 feet (914 m) but were not detected in unburned grassland or nearby burned or unburned chaparral. Chaparral habitat was dominated by chamise on south-facing slopes. In mesic environments, chaparral habitat was dominated by chamise, ceanothus (Ceanothus spp.), and Nutall's scrub oak (Q. dumosa). Fire severities were not given [156].
Frequent fire may not be essential in acorn woodpecker habitat. In foothill oak-pine woodlands in the San Joaquin Experimental Range in Madera County, California, acorn woodpeckers preferred nesting in areas containing a high density of logs (1.5% cover of logs ≥ 2 inches (5 cm) diameter). Habitat was dominated by blue oak, interior live oak, and foothill pine. Study areas had been lightly to moderately grazed by livestock for 100 years and lightning fires had been suppressed before they reached 10 acres (4 ha) in size [111,112].
The following table provides fire regime information on vegetation communities in which acorn woodpeckers may occur, based on the habitat characteristics and species composition of communities acorn woodpeckers are known to occupy. There is not conclusive evidence that acorn woodpeckers occur in all of the habitat types listed, and some community types, especially those used rarely, may have been omitted. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
This review cites data collected primarily from 2 acorn woodpecker subspecies: the Pacific Coast subspecies, Melanerpes formicivorus bairdi, located at the Hastings Natural History Reservation in Monterey County, California (hereafter referred to as "Hastings Reservation"); and the southwestern subspecies, (M.f. formicivorus), located at Water Canyon in the Magdalena Mountains of New Mexico [87,133,134] and the Research Ranch in Elgin, Arizona [132].
Social organization: Acorn woodpeckers are cooperative breeders with complex social behaviors. The quantity and quality of stored acorns influence group size and composition, reproductive success, and survivorship [67,72,78,122]. Acorn woodpecker groups defend year-round territories, cooperatively store acorns in 1 or more granaries (see Food habits), produce 1 nest at a time, and raise offspring together [72,90,91]. Acorn woodpecker groups consist of 2 to 15 individuals, with an average of 5 or 6 individuals [72,74,78,89,132]. Within groups, there are 1 to 4 breeding males, 1 or 2 (rarely 3) breeding females, and 0 to 10 non-breeding offspring born in previous years. Territories that are continually occupied during the breeding season contain more breeding males and more nonbreeders than territories that are intermittently occupied [72]. Genetic relatedness is high [72], but close inbreeding rarely occurs [72,74]. At Hastings Reservation, mean adult group size over an 11-year period was 4.4 individuals (SD 2.4) (range not given) during the breeding season. Nearly all groups (97.6%) contained at least 1 breeding male and female. Monogamous pairs of acorn woodpecker were also common [72]. At the Research Ranch and in the Huachuca Mountains of Arizona, mean breeding group size was 2.64 individuals (SD 0.89) (range 2.0 to 5.0). At Water Canyon, mean group size was 2.15 individuals (SD 0.36) (range 2.0 to 3.0) [75]. For comparative breeding data on acorn woodpeckers at Hastings Reservation, the Research Ranch, and Water Canyon, see Koenig and Haydock [70].
The southwestern subspecies of acorn woodpecker exhibits social plasticity due to marginal habitat. They may either live in highly cooperative resident groups or migrate independently (presumably to oak woodlands in the Sierra Madre of northern Mexico) during winter and return in spring to form temporary male-female bonds. In oak savanna and oak woodland habitats at the Research Ranch, some acorn woodpeckers lived in family groups consisting of 3 birds; they stored acorns in granaries. Most acorn woodpeckers, however, lived independently and stored few acorns. Both types of behavior may be present within the same population at any given time, and acorn woodpeckers may shift between strategies, depending on acorn production. During years of good acorn production, acorn woodpeckers are able to remain resident and form stable social groups. During years of poor acorn production, limited acorn stores are consumed quickly, forcing migration [132].
Breeding: Acorn woodpeckers are considered opportunistically polygynandrous [72,75], meaning that 2 or more males mate with 2 or more females within a social group. Monogamy is also common [72,132]. Acorn woodpeckers are typically cooperative breeders [72,76,78]. Within a group, up to 4 males may mate with up to 3 females, and females lay eggs in a communal nest [72,78]. Genetic relatedness is high within an acorn woodpecker group; however, close inbreeding is usually avoided. Breeding males are generally unrelated to breeding females. Breeders are typically closely related to each other within each sex. Male breeders are generally siblings or a parent and 1 or more offspring, and the same is true for female breeders [72]. Age of first reproduction at Hastings Reservation is 2.1 years for males and 1.9 years for females [72].
Breeding and nesting occur from late March to late June and peak in April. Breeding may occur again between late August and mid-October if weather is mild and stored acorns are still available [72,76,77]. Of 1,173 nests found over a 31-year period at Hastings Reservation, 51 nests (4.3%) produced a second brood during fall [77]. In Arizona and New Mexico, mating typically occurs in late June, and a second nesting is rarely attempted during fall [132].
Reproductive success: Many factors influence reproductive success. They may include availability of stored acorns, abundance of flying insects (see Food habits), reproductive competition, prior breeding experience, territory quality, group size, granary size, and weather [67,72,75]. According to some researchers, availability of stored acorns in spring has the largest influence on reproductive success [72,75,76]. According to Koenig [68], breeding is impossible if acorn stores have been exhausted by spring. However, according to Roberts [122], reproductive success is not significantly (P>0.10) related to number of stored acorns, but is related to availability of arthropods, which contain more protein than acorns. Reproductive success may be poor the first spring after a bad acorn crop [72]. At Hastings Reservation, large acorn crops permitted the storage of more acorns and significantly (P≤0.001) increased reproductive success the following spring [67]. Groups of acorn woodpeckers that had not exhausted acorn stores by spring nested earlier, had larger clutches, a higher proportion of eggs that hatched, a higher proportion of young that fledged, and higher survival of young the first winter. The following table compares reproductive success of acorn woodpecker groups with and without stored acorns in May [72]:
Comparative reproductive success of acorn woodpecker groups at Hastings Reservation [72]* Groups with acorn stores present in May Groups with acorn stores exhausted by May Mean group size (SD) 4.57 individuals (2.24) (n=139) 3.44 individuals (2.03) (n=43) Mean first laid egg date (SD) 7 May (23.7 days) (n=157) 30 May (36.4 days) (n=20) Mean clutch size (SD) 4.55 individuals (1.03) (n=93) 3.57 individuals (0.65) (n=14) Eggs hatched (%) 69.0 (n=578) 54.2 (n=59) Young fledged (%) 47.6 (n=578) 25.4 (n=59) Hatchlings that fledged (%) 68.9 (n=399) 46.9 (n=32) Mean number of young fledged (SD) 2.89 individuals (1.87) (n=137) 0.51 individuals (1.11) (n=43) Mean number of young alive in February (SD) 1.62 individuals (1.53) (n=104) 0.34 individuals (0.79) (n=32) Groups successful (young surviving through their first winter) (%) 82.7 (n=139) 23.3 (n=43) *All differences presented here are significant at P<0.05Reproductive competition between joint-nesting females negatively affects reproductive success. Approximately 25% of acorn woodpecker groups consist of 2 or more nesting females sharing a communal nest at any one time. Joint-nesting females compete to lay their eggs in the nest and may destroy eggs laid by co-breeders. Females that are last to lay eggs in the communal nest benefit by destroying eggs laid earlier by co-nesters. Destroyed eggs are compensated for by laying more eggs. Therefore, groups with joint-nesting females lay significantly (P<0.001) more eggs than monogamous females, but reproductive success per female is lower [73]. On a per female basis at Hastings Reservation, monogamous pairs of acorn woodpeckers fledged significantly (P≤0.05) more young on average (2.72 young (SD 1.69), n=29) than groups that consisted of 2 reproductively active females (1.32 young (SD 1.33), n=11) [67].
At Hastings Reservation, the most important factors influencing reproductive success were prior breeding experience and yearly variation in food, weather, or other ecological conditions. Acorn woodpecker groups in which the breeding membership did not change from the prior breeding season had significantly (P≤0.01) higher reproductive success than groups that experienced turnover in breeding membership [67]. For more information on factors influencing reproductive success at Hastings Reservation, the Research Ranch, and Water Canyon, see Koenig and Stacey [75].
Incubation period and clutch size: The incubation period averages 11.5 days [67]. For the first week of incubation, 1 male and 1 female tend the eggs. Approximately 1 week after eggs are laid, all birds in the group, regardless of sex, take turns incubating the eggs, and later feeding the young [89]. Overall, adult females incubate eggs more often than adult males, and adult males brood and feed nestlings more often than adult females [91]. Acorn woodpeckers produce at least 1 brood/year across their range, but have been observed producing a second brood at Hastings Reservation [77]. Large acorn woodpecker groups (7 to 8 birds) do not produce more offspring per capita than monogamous pairs [67], and reproductive success of joint-nesting females is lower than that of monogamous females [73]. Clutch size at Hastings Reservation averaged 4.82 eggs/nest (SD 1.39) for joint-nesting females and 4.36 eggs/nest (SD 1.04) for monogamous females [68,72]. In riparian habitat in the Magdalena Mountains, mean reproductive rate over a 10-year study period was 2.01 young/pair (range 0.05 to 4.00, n = 433) [134].
Development: Across the acorn woodpecker's range, the complete nesting cycle takes approximately 45 days to complete (4 days for egg-laying, 11 days for incubation, and 30 to 32 days for young to develop before fledging) [68,72,135].
Mortality and survival rates: Major causes of mortality include nestling starvation [72], predation [73,135], egg destruction by joint-nesting females, and acorn availability [72]. Starvation is a major cause of nestling mortality at Hastings Reservation. Of 693 eggs laid in 180 nests, 16.0% produced nestlings that starved [75]. Predation of eggs is mainly by snakes [55,72,75] and Cooper's hawks (Accipiter cooperii) [91,135] (see Predators). Percentage of juveniles lost to predators at Hastings Reservation was 7.9% (n=31 nests)[72]. Most egg mortality occurs from destruction by conspecifics [73] (see Reproductive success).
At Hastings Reservation, survivorship of acorn woodpeckers was significantly (P<0.001) influenced by acorn availability. For example, the winter following a poor acorn crop, disappearance and probable mortality of females was 46.2% (n=13), compared to 5.8% (n=137) the winter following a good acorn crop [75]. Survivorship was higher on permanently occupied territories compared to those not permanently occupied [72].
Adult survivorship is higher than juvenile survivorship [75,134]. At Hastings Reservation, mean annual survivorship was 82.4% (n=273) for breeding males and 71.2% (n=302) for breeding females. Survivorship of first-year birds was 57% (n=447) [75]. Over a 9-year study in the Magdalena Mountains, mean annual adult survivorship was 59% (range 38% to 71%, n=397). Mean juvenile survivorship was 35% (range 18% to 64%, n not given) [134]. In Water Canyon, mean annual survivorship was 61.3% for breeding males and 51.5% for breeding females. Survivorship of first-year birds was 37% (n=123) [75].
The oldest recorded acorn woodpecker at Hastings Reservation was at least 16 years for a male and at least 15 years for a female. The oldest recorded individuals in Water Canyon were at least 9 years for a male and at least 5 years for a female [76].
Dispersal: Young remain in their natal group for at least the first year [89]. After the first year, offspring either stay in their natal group as non-breeders or disperse to become breeders in vacant spots within other acorn woodpecker groups. Offspring that remain in their natal area are nonbreeding "nest helpers" for several years. They may eventually become breeders within their natal group after the death of breeders [71,72]. Dispersal occurs during spring and may occur during late summer to early fall. In Arizona, acorn woodpeckers may migrate during winter and return in spring to nest in territorial breeding pairs [78,132] (see Social organization). During spring, some juveniles may disperse from their natal group and either join other groups of acorn woodpeckers or colonize abandoned acorn woodpecker territories. During late summer to early fall, dispersal may involve groups of juvenile and adult acorn woodpeckers, and is typically a response to acorn crop failure [91].
Male acorn woodpeckers dispersed shorter distances and inherited natal territories more often than female acorn woodpeckers at Hastings Reservation. Of 70 breeding males and 87 breeding females that dispersed, mean dispersal distances were 0.34 mile (0.54 km) for males and 0.41 mile (0.66 km) for females, a significant difference (P<0.01) [71]. Of 137 male and 22 female acorn woodpeckers at Hastings Reservation, males inherited 23.7% and females inherited 4.6% of their natal territories [71].
Territory size and density: Territories are established in habitats that meet acorn woodpecker requirements during summer and winter [91], and the same territory may be used for generations of acorn woodpeckers [91]. Acorn woodpeckers typically defend permanent, all-purpose territories [66,91]; however, acorn woodpecker groups may disband and leave their territory if an acorn crop fails or a granary tree is destroyed [66,72,106].
Territories typically encompass 10 to 15 acres (4-5 ha) [89,91], and are circular or hexagonal in shape, which may be optimal for energetic efficiency and for storage of fluctuating resources [122]. At Hastings Reservation, territory size ranged from 8.6 acres to 22.2 acres (3.5-9.0 ha), with a mean of 14.8 acres (6.0 ha) and a density of 6.7 territories/100 acres [91]. Most territories at Hastings Reservation are along or adjacent to watercourses or in old fields on hilltops with scattered oaks [72].
Roberts [121] found that in California and Arizona, territory size was not strongly related to acorn woodpecker group size. In contrast, MacRoberts and MacRoberts [91] found a significant positive rank correlation (P<0.01) between group size and territory size in California. As group size increased over time, territory size increased, but the opposite did not occur, so some small acorn woodpecker groups had disproportionately large territories [91].
In blue oak woodlands in Mendocino County, California, density of acorn woodpeckers was 25.6 individuals/40 ha [155]. In habitat dominated by blue oak with varying amounts of coast live oak in Monterey and San Luis Obispo counties, California, acorn woodpeckers occupied an annual average of 0.2 territories/40 ha during the spring of 1994 and 1995 [149].
Acorn woodpeckers influence the composition, structure, and distribution of oak woodlands [17]. The acorn woodpecker is considered by some biologists as a keystone species because it provides tree cavities for birds and other animals that cannot create their own cavities [17,83,152]. In California, the acorn woodpecker is considered a "focal species", which is defined as a species chosen for special attention in a multi-species planning effort. Focal species may be used to guide components of conservation planning such as selection and design of habitat reserves, habitat restoration and management, and population monitoring [30].
Management considerations for the acorn woodpecker vary by region and vegetation type.
Oak woodlands and forests in the Pacific Northwest: Oak woodland habitats are threatened in western Washington, western Oregon, and California due to urban development, agriculture, logging, firewood cutting, and conifer encroachment from fire exclusion [47,83,93,158]. Additional threats include lack of regeneration of several key tree oak species [158] and sudden oak death in coast live oak, tanoak, California black oak, and Shreve oak (Q. parvula var. shrevei) in Oregon and California [27,32,38,40,41,102].
In Oregon white oak woodlands in Washington and Oregon, thinning dense stands to increase diameter and production of mast trees [107] may benefit acorn woodpeckers by creating potential granary trees [61]. For oak restoration and enhancement recommendations in western Washington, see Larsen and Morgan [83]. Wilson and others [155] recommend maintaining a variety of oak species in acorn woodpecker habitat to ensure acorn production at any one point in time.
Jackman [59] recommends the following silvicultural management in Pacific Northwest forests for all woodpecker species: 1) place tracts of land >99 acres (40 ha) on 100-year, 200-year, 300-year, or longer rotations, allowing development into mature forest with a minimum of human interference; 2) do not cut standing dead trees; 3) retain dying trees, insect infested trees, dead-topped trees, distorted or wind-broken trees, and trees with heartwood rot on precommercial and commercial thins; 4) retain slash and logs for potential foraging sites; and 5) attempt to duplicate the tree species composition of a stand following timber harvest [59].
Grassland and chaparral in the Pacific Northwest: Grassland and chaparral (Ceanothus spp.-Manzanita spp.) habitat have been lost and/or degraded in western Washington and western Oregon due to expanding human populations [5]. Altman and others [5] recommend the following management for wildlife, including acorn woodpeckers, in these habitats: 1) inventory habitat types and their degree of modification, 2) protect high-quality sites and restore degraded habitats, and 3) manage to maintain habitat quality and wildlife populations.
Oak woodlands and oak-pine woodlands in California: Key recommendations for preserving oak woodlands in California include prioritizing the protection of sites with intact oak regeneration, encouraging the replacement of weedy annual grasses with native perennial grasses in the understory, using prescribed fire (see HABITAT RELATED FIRE EFFECTS), and maintaining and enhancing natural vegetation corridors between oak woodlands and adjacent habitats [158]. Stralberg and Williams [138] recommend the following management for birds in foothill oak woodlands in California: 1) preserve remaining large (>40 acres (16 ha)), undeveloped parcels of oak woodlands; 2) limit subdivisions of rural parcels into small (1.0 to 5.0 acre (0.4-2.0 ha)) ranchettes; 3) manage small parcels of oak woodlands to retain components including large trees, snags, and interior live oaks; and 4) maintain a mosaic of habitat types.
In 1978, Gutierrez and Koenig [46] recommended the following management in California oak-pine woodlands for acorn woodpeckers: 1) evaluate existing and potential granary trees before removing any and, based on acorn woodpecker territory size, attempt to protect or provide ≥15 primary granary trees/100 acres; 2) if 2 or more granary trees are located close to each other, remove the one with the smallest number of storage holes if removal is necessary at all; 3) maintain old, large, living trees for potential storage trees; and 4) where firewood cutting is permitted, protect granary trees.
Oak-pine woodlands in the southwestern United States: For breeding birds in southwestern ponderosa pine-Gambel oak habitat, Rosenstock [124] suggests providing a mix of Gambel oak growth forms by retaining and recruiting mature and old-growth oaks wherever possible and enhancing regeneration and recruitment of younger oak growth forms by using prescribed fire and other treatments.
Sudden oak death disease: Sudden oak death disease, caused by a fungus-like water mold, Phytophthora ramorum, may be a threat to acorn woodpeckers [93,102]. Sudden oak death was detected in 1995 and involves tanoaks and red oaks (Erythrobalanus), some of which are endemic to North America. Sudden oak death has caused mortality of coast live oaks in central California [40,41,102] and tanoaks in Oregon and coastal California [27,32,38]. All sizes and ages of tanoak are susceptible to leaf, branch, bole, bark, and/or root infection [27], and Phytophthora ramorum infection is nearly always fatal to tanoaks, although mature trees may take several years to die [9]. In 2006, Monahan and Koenig [102] used 3 regression models to predict how sudden oak death disease would impact oak-dependent bird species. The predictions ranged from severe to mild effects. Results were averaged across the 3 models to provide the best current estimated effects of sudden oak death on birds. Using those values, they estimated a 50% decline in acorn woodpecker populations in coastal California [102].
Snags and coarse woody debris: Acorn woodpeckers use snags and coarse woody debris for storing acorns, nesting, and roosting [10,29,55,57,76,95,129] (see Preferred Habitat). The number of snags available in an area may determine density of cavity-nesting species, including acorn woodpeckers [59]. An abundance of snags of various ages and sizes ensures nesting and foraging opportunities for woodpeckers [83].
Ohmann and others [104] suggest retaining large snags and live trees during harvesting and thinning operations for woodpecker species. Based on literature reviews, at least 5 large snags (>12 inches (30 cm DBH))/ha should be retained for cavity-nesting birds [49].
To ensure availability of dead and dying wood for wildlife habitat in general, Bunnell and others [23,24] suggest using a variety of practices. They recommend retaining preferred species and a range of age classes and sizes of dead wood including some large trees and snags. Trees >12 inches (30 cm) DBH in inland habitat, and conifers >20 inches (50 cm) DBH in coastal habitat would accommodate most bird species [23,24], though acorn woodpeckers tend to prefer larger trees for granaries [46,61,91] (see Granaries). Dead and dying trees can also be retained by limiting salvage logging after fire [23,24].
Grazing: Grazing by livestock may or may not affect acorn woodpeckers. In habitat dominated by gray pine, interior live oak, and blue oak in the western foothills of the Sierra Nevada, acorn woodpeckers were not affected by grazing (P=0.3359). Mean numbers of acorn woodpeckers were 4.8 birds (SD 1.8) on ungrazed plots, and 5.2 birds (SD 1.6) on grazed plots. Possible concerns related to grazing include reduction in shrub, forb, and grass cover; increased abundance of European starlings, which compete with acorn woodpecker for nest cavities; and increased abundance of brown-headed cowbirds (Molothrus ater) which may parasitize acorn woodpecker nests [152].
According to Zwartjes and others [159], acorn woodpeckers are a priority species in the southwestern United States, meaning that they should receive greater consideration than non-priority wildlife species in planning related to livestock grazing. In Arizona and New Mexico, intensive grazing by livestock in ponderosa pine woodlands contributes to suppression of low severity fires by reducing fine fuels. Lack of fire encourages shrub growth and conifer encroachment. Dog-hair thickets of young conifers increase the risk of severe fire that could kill mature ponderosa pines. Livestock may also browse deciduous tree seedlings, which affects long-term recruitment of large trees [159] and may ultimately reduce acorn woodpecker habitat.
Other: In a study conducted in Santa Clara Valley, California, acorn woodpeckers were sensitive to urbanization due to either a shortage of mature trees containing cavities or competition with European starlings for tree cavities [126]. European starlings may compete with acorn woodpeckers for tree cavities; however, acorn woodpeckers may be capable of defending nest holes due to their communal nature [131]. In southern Arizona and New Mexico, acorn woodpeckers provide elf owls (Micrathene whitneyi) [95], purple martins (Progne subis) [95,129,154], western bluebirds (Sialia mexicana) [10], and violet-green swallows (Tachycineta thalassina) with nest cavities [95].
Acorn woodpeckers are sensitive to firewood cutting and rangeland modification in blue oak woodlands in the northern Sacramento Valley, California. Sensitivity was high only when "substantial" differences occurred between cut and uncut woodland conditions [42].
In coast redwood forests in northern California, acorn woodpeckers use "legacy trees" [97]. Legacy trees are defined by Mazurek and Zielinski [97] as old-growth trees that have been spared during harvest or have survived stand-replacing natural disturbances. Due to the rarity of legacy trees, it is recommended that their locations be determined and that they be protected from logging or other physical degradations [97].
Acorn woodpeckers are oak woodland specialists [93]. Their demography is limited by acorn productivity and the ability to store mast [76]. Oak-pine woodlands [59,76,82] and habitat containing mature oaks interspersed with grassland are preferred [59,89]. These habitats may occur from sea level to mountainous areas within the distribution of oaks [76].
Essential habitat elements for the acorn woodpecker include acorn-producing trees, tree cavities, and snags [30,72,122]. Oaks >17.9 inches (45.5 cm) DBH are sought for collecting acorns [101] and roosting [95,122]. Pines and other conifers are preferred for nesting and for storing acorns due to their soft wood and/or thick bark [95,122]. Storage space (granaries) is a greater limiting factor in acorn woodpecker habitat than acorn availability [72].
Acorn woodpeckers are generally found in habitat containing more than one oak species [76]. Because different species of oaks do not produce synchronous crops, acorns are usually a reliable food source during fall [70,72,76]. In the southwestern United States, only riparian habitat in canyon bottoms of isolated mountain ranges produces enough acorns to support acorn woodpeckers throughout the winter. Therefore, acorn woodpecker populations are small and discrete in those areas [70,133,134].
Each generation of acorn woodpecker depends on habitat modifications of the previous generation. Habitat previously occupied by other acorn woodpeckers is preferred because it already contains granary trees, sap trees, and trees with cavities for nesting and roosting. Habitat without these features is rarely occupied by acorn woodpeckers [91,122].
Stand composition/structure: Acorn woodpeckers prefer habitat containing oaks [123,124,147], mature forest with large-diameter trees [115,118,155], an open stand structure [34,143,155], and a diversity of oak species [19,70,72,122].
In 3 studies conducted in northern Arizona, oaks were an essential component of acorn woodpecker habitat; however, acorn woodpeckers were found occasionally in pure ponderosa pine forest. Acorn woodpeckers were detected more often in ponderosa pine-Gambel oak woodlands than pure ponderosa pine forest in several sites throughout northern Arizona. Twenty-three stands, defined as contiguous areas of structurally similar forest ≥100 acres (41 ha), were chosen for the study. Twelve stands were located in ponderosa pine-Gambel oak habitat, and 11 stands were located in pure ponderosa pine habitat. In ponderosa pine-Gambel oak stands, acorn woodpeckers were detected most often in old logged areas where trees were 5.0 to 11.9 inches (12.7-30.2 cm) DBH. Within pure ponderosa pine forest, acorn woodpeckers were detected only in unlogged stands with a history of either wildfire or prescribed fire in the previous 20 years [123]. Although not indicated, Gambel oak was more than likely located in the vicinity of pure ponderosa pine stands and was probably used as a food source for acorn woodpeckers.
In a similar study on the Coconino National Forest and the Arizona Army National Guard Camp Navajo, Arizona, acorn woodpeckers occurred in ponderosa pine-Gambel oak stands 3 times more often than in pure ponderosa pine stands. Both cover types had an understory of Arizona fescue (Festuca arizonica) or blue grama (Bouteloua gracilis). Stands were ≥49 acres (20 ha) and contained contiguous areas of structurally similar forest. Stands did not have significantly (P>0.05) different density, canopy cover, diameter, basal area of ponderosa pine, or snag density. The ponderosa pine-Gambel oak habitat contained a mixture of shrub-like and tree growth forms of Gambel oak [124].
Of 6 study plots dominated by ponderosa pine, Gambel oak, and occasional alligator juniper (Juniperus deppeana) in the Coconino National Forest, Arizona, acorn woodpeckers (3.0 breeding pairs) were found in only 1 plot. The plot with acorn woodpeckers contained the highest density of Gambel oak. Details of the plot composition are shown in the table below [147]:
Composition of stands in preferred acorn woodpecker habitat in Coconino National Forest, Arizona [147] Relative density Relative dominance Relative frequency Importance value Absolute density (trees/ha) Ponderosa pine 86.8 91.9 74.3 253.0 59.7 Gambel oak 13.2 8.1 25.7 47.0 9.0Mature forest containing large-diameter conifers and oaks is an important component of acorn woodpecker habitat. One oak species may sometimes be preferred over other oak species. In a 1988 study in the Six-Rivers, Klamath, and Shasta-Trinity National Forests in California, acorn woodpeckers preferred mature Douglas-fir forest mixed with tanoak and Pacific madrone (Arbutus menziesii) over early seral stages. Mature stands were generally >100 years old and contained trees >24 inches (60 cm) DBH and >131 feet (40 m) tall, with a multi-layered canopy, a well-developed understory, and many standing and fallen trees >35 inches (90 cm) DBH. The brush/sapling seral stage lasts up to 20 years following logging and was characterized as mixed or pure stands of shrubs and Douglas-fir seedlings and saplings <20 feet (6m) tall in association with forbs and perennial grasses. The pole/sawtimber stage persists up to 150 years following logging and consists of trees 20 to 131 feet (6-40 m) tall, with crowns up to 26 feet (8 m) in diameter. The following table shows densities of acorn woodpeckers in different successional stages [118]:
Density of acorn woodpeckers in 3 successional stages of Douglas-fir forest in northern California [118]Successional stage
Brush/sapling Pole/sawtimber Mature Density of acorn woodpeckers (individuals/100 ha) 0 1.0 1.9The authors predicted that given logging trends at that time (1988), 85% of mature Douglas-fir stands would be replaced by younger age classes in 50 years, and acorn woodpecker populations could subsequently decline [118].
Acorn woodpeckers were also detected more frequently in mature forest than in young or old-growth forest in southwestern Oregon and northwestern California. Habitat was dominated by Douglas-fir in association with tanoak and Pacific madrone; stand ages were not given [115].
In blue oak woodlands in Mendocino County, California, acorn woodpeckers utilized habitat containing large-diameter trees (mean >20 inches (50 cm DBH)). Tree species found on study plots included blue oak, interior live oak, coast live oak, canyon live oak (Q. chrysolepis), valley oak, Oregon white oak, black oak, Oracle oak (Q. Ã morehus), California buckeye (Aesculus californica), California bay (Umbellularia californica), Pacific madrone, and Oregon ash (Fraxinus latifolia). Acorn woodpeckers excavated cavities most often in blue oak and used Oregon white oak in proportion to its availability. Number of natural tree cavities increased significantly (P<0.001) with tree diameter for all tree species combined. Number of excavated cavities also increased significantly (P<0.001) with tree diameter for all tree species combined and for all species except evergreen oaks and California buckeye [155].
Acorn woodpeckers generally prefer an open stand structure. In the Siskiyou National Forest, Oregon, acorn woodpeckers selected clearcut areas with residual Douglas-fir trees and either abundant tanoak or California black oak nearby. According to the authors, the clearcut created a habitat structure similar to pine-oak savannas, which may have attracted acorn woodpeckers. Douglas-fir trees within clearcuts had been "topped" by Forest Service personnel to provide wildlife trees. Topped trees were used by acorn woodpeckers for granaries, nests, and perch sites to hawk insects. Other trees used for granaries in the area included sugar pine (Pinus lambertiana) and Jeffrey pine [34].
In habitat dominated by ponderosa pine in the Coconino National Forest, Arizona, breeding acorn woodpeckers were detected only in a severely thinned plot. Five study plots were chosen in homogeneous stands of ponderosa pine, each containing the same proportion of different size classes of trees and densities of Gambel oak. The following table compares the density of acorn woodpeckers between an unlogged control and various logging treatments [143]:
Stand characteristics of logged areas and associated breeding densities of acorn woodpeckers in the Coconino National Forest, Arizona [143] Plot Acorn woodpeckers (pairs/40 ha) detected in 1975 Treatment year Tree density (trees/ha) Canopy volume (m³/ha) Total basal areaIn blue oak woodlands in Mendocino County, California, acorn woodpeckers required habitat containing low tree density (<100 trees/ha). Tree species found on study plots included blue oak, interior live oak, coast live oak, canyon live oak, valley oak, Oregon white oak, black oak, Oracle oak, California buckeye, California bay, Pacific madrone, and Oregon ash [155].
The studies cited above indicate acorn woodpecker preference for open stands, but Raphael and others [118] describe use of mature forest with a multi-layered canopy and "well-developed" understory.
Acorn woodpecker density may be influenced by oak abundance and oak species diversity. Two analyses of Audubon Christmas Bird Count data [19,70] found that abundance of acorn woodpeckers in Pacific Coast populations increased with increasing density of oaks. A field study [121] did not detect this pattern but found some indication that acorn woodpecker group size was positively related to oak density. In southwestern populations, no relationship was detected between oak abundance and acorn woodpecker abundance [19,70]. Based on Audubon Count data, Bock and Bock [19] found that Pacific Coast acorn woodpecker populations increased with increasing oak species diversity, up to about 5 species, and then leveled off. They hypothesized that areas with few oak species were subject to random and frequent acorn crop failures, a pattern borne out by Koenig and Haydock's [70] field research at the Hastings Reservation. Koenig and Haydock [70] also found that, in Pacific Coast populations, year-to-year variation in acorn woodpecker abundance declined with increasing oak diversity (P=0.01), indicating that populations in areas with high oak diversity are more stable than populations in areas with one or a few oak species. In southwestern populations, Roberts' field data indicated a positive relationship between acorn woodpecker abundance and oak species diversity (P<0.05) [121], while Bock and Bock's [19] Christmas Count data did not.
Only 1 study described acorn woodpecker preference for riparian habitat containing Arizona sycamore. In the Huachuca Mountains, acorn woodpeckers were detected in small and large riparian woodland strips dominated by velvet ash (Fraxinus velutina), Fremont cottonwood (Populus fremontii), desert willow (Chilopsis linearis), Arizona sycamore, Arizona walnut (Juglans major), or willow (Salix spp.). They were not detected in riparian habitat dominated by bigtooth maple (Acer grandidentatum). For each tree species, small and large stands were selected in continuous riparian habitat adjacent to open uplands dominated by grass or wooded uplands dominated by oak and/or pine. Control sites for each combination of factors were located in open and wooded areas along drainages with no riparian trees, and several replicate study plots were selected for each combination of factors. Acorn woodpeckers showed a strong affinity for Arizona sycamores regardless of upland vegetation or elevation. Although not indicated, acorn woodpeckers probably obtained food from oaks in nearby wooded uplands. The following table shows characteristics of 13 plots where acorn woodpeckers were detected [139]:
Riparian habitats used by acorn woodpeckers, Huachuca Mountains, Arizona [139] Dominant tree speciesStand size
(small ≤200 m) (large ≥1,000 m)
Acorn woodpeckers are associated with a subset of habitat that is significantly (P<0.05) different than overall habitat. The structure of acorn woodpecker habitat was analyzed for 25 groups of acorn woodpeckers in California and Arizona. Circles were surveyed within a 36-foot (11 m) radius of acorn woodpecker granaries, which were the central activity areas, and in 4 circles expanding 82 to 98 feet (25-30 m) outwards from the center of the circle. Central activity areas contained more tree species (but not more oak species) and more large, high-canopied trees (typically pines) than outside the central activity areas. In addition to granaries, nesting and roosting sites were usually located in the central activity areas. The central activity locus may optimize foraging-flight efficiency when fluctuating amounts of acorns are harvested within a territory. Storage/activity centers were regularly spaced in habitat occupied by multiple acorn woodpecker groups, limiting the potential number of sites where the main granary tree could be located [121]. Burgess and others [25] found that, in contrast to Roberts' [121] study, granaries were significantly (P<0.05) clumped across several neighboring acorn woodpecker territories on the grounds of Stanford University. The authors could not contribute clumping of granaries to clumped habitat resources such as acorns, insects, or tree sap. Clumping of granaries across neighboring acorn woodpecker territories may offer the most advantageous group structure for avoidance of predators and efficient foraging [25].
Nesting: Acorn woodpeckers are strong primary excavators [17,23,24,61,155], creating cavities for nesting and roosting. Cavity excavation is communal and occurs during winter and spring [72]. At Hastings Reservation, nest height averages 27.2 feet (8.3 m) (range 7.5 to 59.1 feet (2.3-18 m)) above ground and nests are most often located in tree trunks. Nests may be constructed in the granary tree but have been recorded up to 0.6 mile (0.9 km) away from the granary tree. Nest holes may be reused. At Hastings Reservation, there is a 50% probability that acorn woodpeckers will reuse nest cavities [76].
Nest cavities may be constructed in snags, live trees [10,29,55,57,76,129], and large (>3 feet (1 m)) or small (<7 inches (17 cm)) limbs [55,155]. Cavities located in live tree limbs are warmer and have less temperature variance than cavities located in dead limbs [55]. Nest cavities in live tree limbs may also provide more protection from predators such as American black bears (Ursus americanus) than nests located in snags [10]. Snags are typically preferred for nesting, however [29,55,57,129].
Snag use by acorn woodpeckers is common [29,129]; logs may also be used, but details on this habit are not available. In an Arizona pine (Pinus ponderosa var. arizonica) forest in Coronado National Forest, Arizona, acorn woodpeckers preferred nesting in ponderosa pine snags ≥20 inches (50 cm) DBH, with a decay stage in which fine twigs were present, sapwood was sound to rotting, and bark cover was 75% to 100%. Density of snags was 4.0 snags/ha [57]. In the Apache-Sitgreaves National Forest in Arizona, cavity nesting birds, including acorn woodpeckers, preferred snags that retained an average of 90% bark cover (range 60% to 100%) for nesting. Snags that had been dead >5 years and were >19 inches (48 cm) DBH were also preferred. Two acorn woodpecker nests were found in ponderosa pine snags, and 1 nest was found in a quaking aspen snag. Mean tree height of the 3 nesting trees was 40 feet (12 m) (range 30 to 50 feet (9-15 m)) and mean DBH was 19 inches (48 cm) (range 14 to 26 inches (36-66 cm)) [129].
Acorn woodpeckers do not show a strong preference for snags an all areas. In ponderosa pine-Gambel oak woodlands in western New Mexico, more acorn woodpecker nests were located in live trees than in snags or dead limbs [10]:
Frequency of acorn woodpecker nests found in snags, dead portions of trees, and live trees (n=15 nests) [10] Snags Dead portions of trees Live trees 5 2 9Of 238 acorn woodpecker nests found in the Pacific Northwest, 7.8% were located in snags [55,129]. Minimum DBH of snags used for nesting by acorn woodpeckers in the Pacific Northwest is 10 inches (25 cm), and minimum height is 15 feet (5 m) above ground [13].
Only 7 of 222 nests occurred in snags at Hastings Reservation, which was significantly more than expected based on snag availability (P<0.001). Nest cavities were found in granary trees 42% of the time, which was more than expected (P <0.001) [55].
Nest tree species: Acorn woodpeckers nest in a variety of tree species, including oak [10,33], ponderosa pine [33,76], Fremont cottonwood [57], Douglas-fir [34,115,117,118], Pacific madrone (>12 inches (30 cm) DBH) [116,117], and California sycamore [55].
Small-diameter Gambel oak trees are utilized more often by cavity nesters than small-diameter ponderosa pine [33]. In a study conducted in northern Arizona, acorn woodpeckers nested in Gambel oaks with a mean diameter of 15 inches (38 cm) and ponderosa pines with a mean diameter of 28 inches (71 cm). In areas where ponderosa pine is uncommon, Gambel oak may be particularly important to cavity nesters [33]. In addition, nests may be excavated in live Gambel oak, whereas excavation is uncommon in live ponderosa pine [123].
In ponderosa pine-Gambel oak habitat in the Black Range, San Mateo, Magdalena, and Zuni mountains in western New Mexico, acorn woodpeckers nested in Gambel oak most often [10]:
Frequency of acorn woodpecker nests found in 8 tree species [10] Ponderosa pine Narrowleaf cottonwoodAcorn woodpeckers nested in Douglas-fir and Pacific madrone trees in the Six-Rivers, Shasta-Trinity, and Klamath National Forests in California [117]. Based on the breeding density of 8.6 pairs of acorn woodpecker/247 acres (100 ha), Raphael [117] estimated that 30 Pacific madrones >12 inches (30 cm) DBH/247 acres are needed to provide nesting substrate each year.
In the Willamette Valley, large-diameter, widely spaced Oregon white oaks provide more cavities for birds than large-diameter Douglas-fir trees [47].
Population vigor in acorn woodpeckers may be associated with nest site selection. At Hastings Reservation, nests located in California sycamore fledged more acorn woodpeckers than nests in all other tree species (valley oak, blue oak, California black oak, and coast live oak) combined (P=0.05). Mean group size of acorn woodpeckers was significantly larger when nests were located in live limbs (4.5 individuals) compared to dead limbs (3.8 individuals, P=0.01) and when nest cavities were located in California sycamore (4.8 individuals) compared to other tree species (4.0 individuals, P<0.05) [55].
Granaries: Granaries are used by acorn woodpeckers for acorn storage [35,45,46,60,72,76,89,106,121,155]. There is usually 1 primary granary in an acorn woodpecker group territory, and 1 or more smaller secondary granaries [46,72,76,91,122,132]. Primary granaries are larger and contain more storage holes than secondary granaries [46,72,91,155]. Of 53 acorn woodpecker groups studied at Hastings Reservation, mean number of granaries within a territory was 2.1 (range 1 to 7) [91]. Acorns are harvested during fall and early winter and stored in holes drilled in the granary. The same granaries are used year after year, and new storage holes are continually created [35,45,46,72]. Dead or live trees are used for granaries, as long as they contain deep, dry bark [60], and granaries are typically located in tree trunks or lower tree limbs [76]. The cambium layer is rarely penetrated, so little detrimental effect to the granary tree occurs [106]. Eventually, granary trees are lost to fire, rotting, or falling [46,72]. Granaries may also be located in utility poles, fence posts [72,91,106], pine cones [60,91], eaves and wood trim of buildings [72,91,106], and under clay roof tiles [91]. Acorn woodpeckers in San Diego County, California, stored coast live oak acorns in Coulter pine (P. coulteri) cones, which exceeded 12 inches (30 cm) in length [60]. In Engelmann oak and coast live oak habitat in Santa Rosa Plateau Reserve, California, acorn woodpeckers stored surplus acorns in boulders composed of porphyritic basalt [91]. Granary treeTree species: Tree species used for granaries vary widely and include oaks, pines, firs, redwoods, sycamores (Platanus spp.), and nonnative species [25,72,91]. Pines are preferred over oaks due to their softer bark [46,89,106], and thick-barked oaks, such as valley oak, are preferred over thin-barked oaks [106]. Granary trees used by acorn woodpeckers on the grounds of Stanford University in California included nonnative Canary Island date palm (Phoenix canariensis) and California palm (Washingtonia filifera) [25]. On the east side of the Sierra Nevada, ponderosa pine [53] or Jeffrey pine are used for granaries [64,120]. At the University of California's Hopland Field Station, acorn woodpeckers preferred large (>30 inches (75 cm) DBH)) deciduous oaks for granaries. Use of each tree species for acorn storage was significantly different than availability for primary and secondary (P<0.001) granary trees. Within the acorn woodpeckers' territories, Oregon white oak comprised 10% of all trees, yet almost 50% of primary granary trees and >25% of secondary granaries were located in Oregon white oak. Although blue oaks were used extensively for granary trees, use by acorn woodpeckers was less than expected based on availability [155].
At Hastings Reservation, acorn woodpeckers used valley oak, which had the largest diameter of all trees, most often for granaries. Other granary trees included blue oak, California sycamore, California black oak, and red willow (Salix laevigata) [91]:
Granary tree characteristics at Hastings Reservation [91]Tree species
Average DBH (cm) DBH range (cm) Average height (m) Height range (m) Number of observations Percentage of total Valley oak 99 28-153 14.5 2.4-24.0 88 78 Blue oak 65 28-90 11.5 3.05-18.3 17 15 California sycamore 74 36-128 16.4 9.6-24.0 5 4 California black oak 62 48-76 13.5 12.0-15.0 2 2 Red willow 50 not given 12.0 not given 1 1Acorn woodpeckers collect acorns from a few trees within their territories and do not travel far to collect acorns. Transport of acorns at the Sedgwick Reserve in Santa Barbara County, California occurred within a 492 foot (150 m) radius of the oak tree. Thus, granaries within a territory contained a low number of different maternal genotypes of oaks [45].
Size: Granary size is an important component of territory quality because large granaries result in immediate benefits in food availability. In Water Canyon, acorn woodpeckers that used large granaries containing >3,000 holes had a 58% chance (n=55) of storing enough acorns to last through winter and into the following breeding season. Acorn woodpeckers that used granaries containing <1,000 holes had a smaller chance (9%, n= 62) of their stores lasting through the winter [75].
Acorn woodpeckers tend to select the largest available trees for granaries. At the University of California's Hopland Field Station, the DBH of granary trees was significantly larger than non-granary trees (P<0.001) [155]. In oak-pine woodlands in Monterey County, California, the largest trees provided ample storage space for acorns, contained rotten limbs, and were likely to die before other trees, thus providing additional storage space. Acorn woodpeckers were observed in an area dominated by ponderosa pine, interior live oak, and canyon live oak (Plaskett Ridge), and an area dominated by sugar pine, tanoak, and canyon live oak (Cone Peak). On both sites, primary granary trees were significantly larger than non-granary trees (P-value not given). Secondary granaries were smaller. Fewer storage holes were created in trees on Plaskett Ridge than Cone Peak, probably because a fire killed many pines 5 years prior to the study, preventing optimal storage use by acorn woodpeckers. Characteristics of storage trees used by acorn woodpeckers are summarized in the table below [46]:
Physical characteristics of acorn woodpecker granary trees in 2 California oak-pine woodlands [46] Plaskett Ridge Cone Peak Mean DBH (cm) Storage holes per tree Proportion of trees dead (%) Mean DBH (cm) Storage holes per tree Proportion of trees dead (%) All storage trees 81 750 100 148 2,200 47 Largest storage tree 96 1,020 100 160 2,900 30The immediate area around a granary differs in structure from the surrounding habitat [61,122]. When granary plots were compared to non-granary plots in Oregon white oak woodlands in the Willamette Valley, Oregon, granary plots contained greater oak basal area, shorter shrub height, and larger-diameter granary trees. Three granary trees and 3 non-granary trees were located within each of 20 acorn woodpecker colonies. Habitat was examined within 39 feet (12 m) of granary and non-granary plots. Granaries were selected in the immediate area of high acorn production. Acorn woodpeckers may have selected granary sites with low shrub height to defend against predators and decrease competition for nesting cavities and acorns [61].
Habitat characteristics within granary and non-granary plots in Willamette Valley, Oregon [61] Granary plot Non-granary plot Oak basal area (m²/ha) (SE) 50.1 (4.1) 27.2 (3.0) Shrub height (SE) 18.5 cm (4.3 cm) 45.0 cm (9.5 cm) DBH of granary tree (SE) 64.7 cm (4.7 cm) 53.5 cm (5.5 cm)Other: Not all acorn woodpeckers use granaries. At the Research Ranch and the Huachuca Mountains, some acorn woodpeckers did not live in typical family groups but as pairs (see Social organization). Permanent, year-round family groups used granary trees to store large numbers of acorns, and migratory pairs of acorn woodpeckers did not use granary trees. Migratory individuals stored some acorns under loose bark and natural crevices of oak trees and in power poles for immediate use after oaks ceased acorn production [132].
The scientific name of the acorn woodpecker is Melanerpes formicivorus
Swainson. It is a member of the woodpecker family, Picidae [6,7,8,130]. There are 4
recognized subspecies in North America [6]:
Melanerpes formicivorus angustifrons Baird
Melanerpes formicivorus bairdi Ridgeway
Melanerpes formicivorus formicivorus (Swainson)
Melanerpes formicivorus martirensis (Grinnell and Swarth) [6]
FIRE MANAGEMENT CONSIDERATIONS:
Acorn woodpeckers are adapted to many habitats with frequent, low- to moderate-severity FIRE REGIMES [39,105,142] and do not appear to be negatively affected by fire of those severities in those habitats [57,84,153]. High-severity fire may positively or negatively affect the acorn woodpecker. It may destroy acorn-producing trees, granaries, and trees containing nest cavities, or it may create snags for nesting and roosting [11,48,57,157].
Prescribed burning provides habitat diversity for wildlife in some plant communities [1]. In oak woodlands in the Pacific Northwest, prescribed burning has been used for bird conservation by reducing conifer encroachment, stimulating oak seedling recruitment, and creating multi-aged stands [47,58,153]. Limited data is available on acorn woodpecker response to prescribed burning. In the following 2 studies in California and Arizona, acorn woodpeckers declined slightly following low- to moderate-severity prescribed burns [57,84].
Abundance of acorn woodpeckers remained relatively stable 2 to 3 years following prescribed fires in oak woodlands and oak-chaparral habitat in California [84,153]. In blue oak-coast live oak woodlands in central-coastal California, relative abundance of acorn woodpeckers did not change following low- to moderate-severity prescribed fires. The authors suggest that fall prescribed fires are likely to have less negative impacts on resident breeding birds in California than winter prescribed burns because breeding may commence during or after the initiation of habitat rejuvenation [153]. Similarly, the number of acorn woodpecker pairs remained relatively stable before and after a prescribed fire in oak-chaparral woodlands in Kern County, California. Habitat was dominated by blue oak, gray pine, interior live oak, and wedgeleaf ceanothus (Ceanothus cuneatus). Severity of the prescribed burn was not described, but the fire generated temperatures of 156 °F (69 °C) at a depth of 2 inches (0.8 cm) below ground. Acorn woodpecker densities were compared on a 20 acre (8 ha) plot before the prescribed burn and for 3 years afterwards. The following table shows a slight decrease in occurrence of acorn woodpecker pairs in postfire year 3 [84]:
Occurrence (number of pairs) of acorn woodpeckers before and after prescribed fires in Kern County, California [84] Prefire Postfire year 1 Postfire year 2 Postfire year 3 4 4 4 2.7In habitat dominated by Arizona pine on the Coronado National Forest, acorn woodpecker density declined slightly on burned sites. See the Research Project Summary for more details [57].
Large snags are important habitat features for the acorn woodpecker [10,29,55,57,76,95,129] (see Snags and coarse woody debris). Prescribed fire may either consume or create snags [11,57,157], and generally benefits acorn woodpeckers. In a mixed-conifer forest dominated by ponderosa pine in the Sierra National Forest, California, the greatest loss of preferred snags (ponderosa pines) used by acorn woodpeckers occurred after the first introduction of spring prescribed fire after a long fire-free period (71 years). Snag loss was 34% after the 1st burn and 15% after a 2nd prescribed burn 5 years later, but only 8% on control sites. Initial snag loss was offset by the creation of new snags [11]. Occasional severe fires in oak woodlands may create snags while leaving most large oaks alive, depending on species of oak [157] (see HABITAT RELATED FIRE EFFECTS).
Large snags should be protected for acorn woodpeckers during prescribed burning when possible [11,57]. In a mixed-conifer forest dominated by ponderosa pine in the Sierra National Forest, California, Bagne [11] recommend protection of ponderosa pine snags, especially during the first application of prescribed fire in fire-suppressed areas. In Arizona pine forests, Horton and Mannan [57] recommend protection of large Arizona pine snags (>20 inches (50 cm DBH) by constructing fuel breaks around the trees before conducting prescribed underburns in forests where large snags have been reduced by logging. Salvage logging would likely decrease the density of large snags used for nest cavities [23,24,48]. Large live trees are important to acorn woodpeckers for nesting, roosting, and for granaries [46,60,75,155] (see Preferred Habitat), and may also require protection during prescribed burning.
Specific fire management recommendations for the acorn woodpecker are scarce. Generally, low-severity burning of understory vegetation may be beneficial in most acorn woodpecker habitat (oak woodlands, pine-oak woodlands, and ponderosa pine forests) to decrease conifer encroachment, initiate sprouting of oaks, reduce fuel loads, and prevent loss of mature oak trees [1,4,16,36,39,47,47,52,58,85,86,101,142,153]. According to Huff and others [58], benefits of prescribed fire to birds are uncertain in oak woodlands and savannas dominated by Oregon white oak or California black oak due to human alteration such as livestock grazing [58]. Fire management considerations for the acorn woodpecker are not available for riparian habitat in the southwestern United States.
Hasta 5 individuos pueden incubar los huevos y alimentar a los polluelos.
Se han observado 11 individuos forrajeando juntos, sin encuentros agresivos en un sólo árbol de roble.
Son expertos atrapamoscas, volando desde tocones o postes de cerca.
Distribucion General: Se encuentra desde el oeste de E.U.A. hasta Colombia.
Melanerpes formicivorus ye un picatueru de tamañu mediu.
Los adultos tienen la cabeza, l'envés, les nales y la cola negres; la frente, el gargüelu, el banduyu y el mantu, blancos. Los sos güeyos son tamién blancos. Los machos adultos tienen el pileu dafechu coloráu ente que les femes presenten una franxa negra ente la frente blanca y el pileu coloráu.
Habiten en carbayeres, dende'l sur de los Estaos Xuníos hasta Colombia. Añeren n'árboles o cañes muertes, en grandes cuévanos escavaos pola pareya. Na cría suelen participar dellos individuos adultos: los estudios de campu amuesen qu'estos grupos pueden tar constituyíos por pareyes criadores monógames o hasta por colectivu de siete machos y tres femes (con más de 10 ayudantes non criadores).
Los grupos criadores crean auténtiques despensas nes qu'atropen abiyotes: escaven furacos nos árboles muertos y almacenar ellí. Estes abiyotes queden a la vista, asína que'l grupu va defender l'árbol de posibles robos. Les abiyotes constitúin una parte importante de la so dieta; tamién comen inseutos que prinden de la corteza de los árboles o qu'atrapen en vuelu, amás de frutos, granes y, dacuando, cazumbre.
Ye una especie residente permanente. Pero, si nun hai abiyotes disponibles pueden emigrar a otra área.
Añalmente pueden cavar 60,000 furacos nun árbol con abiyotes ya inclusive lo introducen en distintos pa cubrir completu asina van evitar qu'otru individuu furtiar.
Esta páxina forma parte del wikiproyeutu Aves, un esfuerciu collaborativu col fin d'ameyorar y organizar tolos conteníos rellacionaos con esti tema. Visita la páxina d'alderique del proyeutu pa collaborar y facer entrugues o suxerencies. Melanerpes formicivorus ye un picatueru de tamañu mediu.
Los adultos tienen la cabeza, l'envés, les nales y la cola negres; la frente, el gargüelu, el banduyu y el mantu, blancos. Los sos güeyos son tamién blancos. Los machos adultos tienen el pileu dafechu coloráu ente que les femes presenten una franxa negra ente la frente blanca y el pileu coloráu.
Habiten en carbayeres, dende'l sur de los Estaos Xuníos hasta Colombia. Añeren n'árboles o cañes muertes, en grandes cuévanos escavaos pola pareya. Na cría suelen participar dellos individuos adultos: los estudios de campu amuesen qu'estos grupos pueden tar constituyíos por pareyes criadores monógames o hasta por colectivu de siete machos y tres femes (con más de 10 ayudantes non criadores).
Los grupos criadores crean auténtiques despensas nes qu'atropen abiyotes: escaven furacos nos árboles muertos y almacenar ellí. Estes abiyotes queden a la vista, asína que'l grupu va defender l'árbol de posibles robos. Les abiyotes constitúin una parte importante de la so dieta; tamién comen inseutos que prinden de la corteza de los árboles o qu'atrapen en vuelu, amás de frutos, granes y, dacuando, cazumbre.
Ye una especie residente permanente. Pero, si nun hai abiyotes disponibles pueden emigrar a otra área.
Añalmente pueden cavar 60,000 furacos nun árbol con abiyotes ya inclusive lo introducen en distintos pa cubrir completu asina van evitar qu'otru individuu furtiar.
Melanerpes formicivorus[1] a zo ur spesad evned eus ar c'herentiad Picidae.
Anvet e voe Picus formicivorus (kentanv) da gentañ-penn (e 1827) gant an evnoniour saoz William Swainson (1789-1855).
Melanerpes formicivorus. Bevañ a ra diwar vez dreist-holl ha kemer amprevaned, frouezh ha sev ivez.
Ar spesad a gaver ar seizh isspesad anezhañ[2] :
Melanerpes formicivorus a zo ur spesad evned eus ar c'herentiad Picidae.
Anvet e voe Picus formicivorus (kentanv) da gentañ-penn (e 1827) gant an evnoniour saoz William Swainson (1789-1855).
El picot menjaglans (Melanerpes formicivorus) és un ocell de la família dels pícids (Picidae) que habita boscos de roures i de roures i pins, des del sud de Washington i nord-oest d'Oregon cap al sud fins al sud de Baixa Califòrnia, des del nord d'Arizona, nord de Nou Mèxic, oest de Texas, Nuevo León i sud-oest de Tamaulipas, cap al sud, fins a l'oest de Panamà, i als Andes de Colòmbia.
El picot menjaglans (Melanerpes formicivorus) és un ocell de la família dels pícids (Picidae) que habita boscos de roures i de roures i pins, des del sud de Washington i nord-oest d'Oregon cap al sud fins al sud de Baixa Califòrnia, des del nord d'Arizona, nord de Nou Mèxic, oest de Texas, Nuevo León i sud-oest de Tamaulipas, cap al sud, fins a l'oest de Panamà, i als Andes de Colòmbia.
Aderyn a rhywogaeth o adar yw Cnocell y mês (sy'n enw benywaidd; enw lluosog: cnocellau y mês) a adnabyddir hefyd gyda'i enw gwyddonol Melanerpes formicivorus; yr enw Saesneg arno yw Acorn woodpecker. Mae'n perthyn i deulu'r Cnocellod (Lladin: Picidae) sydd yn urdd y Piciformes.[1]
Talfyrir yr enw Lladin yn aml yn M. formicivorus, sef enw'r rhywogaeth.[2] Mae'r rhywogaeth hon i'w chanfod yn Ne America a Gogledd America.
Mae'r cnocell y mês yn perthyn i deulu'r Cnocellod (Lladin: Picidae). Dyma rai o aelodau eraill y teulu:
Rhestr Wicidata:
rhywogaeth enw tacson delwedd Cnocell fraith Japan Yungipicus kizuki Cnocell gorunfrown Yungipicus moluccensis_-_Flickr_-_Lip_Kee.jpg)
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Aderyn a rhywogaeth o adar yw Cnocell y mês (sy'n enw benywaidd; enw lluosog: cnocellau y mês) a adnabyddir hefyd gyda'i enw gwyddonol Melanerpes formicivorus; yr enw Saesneg arno yw Acorn woodpecker. Mae'n perthyn i deulu'r Cnocellod (Lladin: Picidae) sydd yn urdd y Piciformes.
Talfyrir yr enw Lladin yn aml yn M. formicivorus, sef enw'r rhywogaeth. Mae'r rhywogaeth hon i'w chanfod yn Ne America a Gogledd America.
Der Eichelspecht (Melanerpes formicivorus) ist ein mittelgroßer Vertreter der Gattung Melanerpes innerhalb der Unterfamilie der Echten Spechte (Picinae). Die auffällige und nicht seltene Art ist vom Südwesten Washingtons südwärts bis ins nordwestliche Südamerika verbreitet. Wie einige andere Melanerpes-Arten leben auch Eichelspechte meist in Familiengruppen, in denen eine höchst differenzierte Sozialstruktur ausgebildet ist. Die geographische Variation ist groß: Es werden über zehn Unterarten beschrieben, von denen sieben allgemein anerkannt sind. Fast alle Unterarten sind Standvögel und betreiben eine intensive herbstliche Vorratshaltung.
Eichelspechte sind mit 22–24 Zentimeter Körperlänge etwa buntspechtgroß. Bei ausreichenden Lichtverhältnissen sind sie in ihrem Lebensraum mit keiner anderen Spechtart zu verwechseln.
Der Rücken und die oberen Flügeldecken sind glänzend schwarz; je nach Lichteinfall irisieren diese Körperpartien grünlich, bläulich oder purpurn. Der Bürzel und die Unterschwanzdecken sind auf weißem Grund unterschiedlich deutlich schwarz gestrichelt. Die Arm- und Handschwingen sind auf der Oberseite weitgehend glanzlos schwarz, im Bereich der Basen der Handschwingen zeigt sich ein weißer Fleck. Die Unterflügeldecken sind schwarz und weisen eine feine weiße Strichelung auf, die Unterseite der Arm- und Handschwingen ist stumpfer schwarz oder braunschwarz. Die beiden zentralen Steuerfedern sind verlängert und laufen spitz zu; häufig, insbesondere bei jungen Individuen, zeigen sie feine weiße oder goldgelbe Einschlüsse. Bei einigen Vögeln sind die Basen der Steuerfedern weiß.
Die Zeichnung und Färbung von Kopf und Gesicht sind recht deutlich geschlechtsdifferenziert. Beim Männchen sind Scheitel und oberer Nackenbereich leuchtend scharlachrot gefärbt; vom unteren Nacken zieht sich ein schwarzes Feld bogenförmig über das Auge, das markant vom Weiß des übrigen Gesichtes begrenzt wird. Der schwarze Schnabel ist an der Basis von einem schwarzen Bereich umgeben; auch der obere Teil der Kehle ist schwarz. Die Brust und der untere Kehlbereich sind weißlich oder gelblich-weiß. Das schwärzliche Brustgefieder weist eine deutliche weiße Zeichnung auf, bei einigen Unterarten sind dort auch rote Federn eingelassen. Die Iris ist weiß. Bei Weibchen ist der scharlachrote Fleck auf den hinteren Scheitel- und oberen Nackenbereich beschränkt. Zur Stirn hin ist er durch ein schwarzes Band von den weißen Gefiederpartien der Stirn getrennt. Beim Männchen grenzt das Rot des Scheitels direkt an das Weiß der Stirnpartie. Füße und Zehen sind dunkelgrau. Männchen sind geringfügig größer und schwerer als Weibchen.
Das Jugendgefieder ist dem Adultgefieder ähnlich, die schwarzen Gefiederanteile sind jedoch etwas heller und weitgehend glanzlos. Der Brustbereich ist häufig bräunlich, die Iris ist schwarz. Die Geschlechtsbestimmung bei Jungvögeln ist schwierig, da Männchen und Weibchen eine gleich große rote Kopfplatte tragen. Am Ende des ersten Lebensjahres mausern Eichelspechte ins Adultgefieder.
Der Flug ist ein für Spechte typischer Bogenflug, wobei im Wellental die Flügel eng an den Körper angelegt werden. Markante Erkennungszeichen sind neben der charakteristischen Gesichtszeichnung der weiße Bürzel und die weißen Flügelfelder im Bereich der Handschwingenbasen.
Familiengruppen des Eichelspechtes sind das ganze Jahr über akustisch sehr auffällig, während sich einzelne Paare bedeutend ruhiger verhalten. Häufigste Lautäußerung sind der oft mit Wäke-wäke transkribierte Begrüßungsruf und ein ebenfalls zweisilbiges, meist gereiht vorgetragenes Element, das sich in etwa mit Jäk-up beschreiben lässt und vor allem in antagonistisch gestimmten Situationen geäußert wird.[1] Daneben sind eine Reihe krächzender und kreischender Laute zu hören. Die Trommelwirbel sind relativ langsam; sie bestehen aus bis zu 20 Einzelelementen.[2]
Das Verbreitungsgebiet des Eichelspechtes reicht vom westlichen, pazifiknahen Nordamerika südwärts über weite Teile Mexikos und Mittelamerikas bis in die nördlichen Andenregionen Kolumbiens. Die nördlichsten Vorkommen bilden kleine, isolierte Populationen im Süden Washingtons; fragmentiert und lückenhaft sind die Brutgebiete in Oregon und im nördlichen Kalifornien. Nach Süden und Südosten zu sind geeignete Mittelgebirgs- und Gebirgsregionen fast flächendeckend besiedelt. Auf der Baja California bestehen zwei kleine isolierte Vorkommen. Nach Südosten ist der Eichelspecht in den Bergregionen Arizonas und Neu-Mexikos und lückenhaft im westlichen und zentralen Texas verbreitet. In Mexiko bewohnt die Art vor allem die lichten Eichenwälder der westlichen Küstengebirge sowie die Gebirgsregionen der östlichen und südlichen Sierra Madre. In Mittelamerika sind die Vorkommen weitgehend auf Bergregionen beschränkt. Weitgehend isoliert von diesen mehr oder weniger geschlossenen Verbreitungsgebieten brütet die Art in den Maya Mountains im südlichen Belize, in den daran angrenzenden guatemaltekischen Gebieten sowie im zentralen Bergland Panamas. An den nördlichen und zentralen Andenabhängen Kolumbiens bestehen voneinander weiträumig getrennte Brutvorkommen.
Da Eichelspechte bei Nahrungsmangel weit umherstreifen, etablieren sie gelegentlich Brutvorkommen weit vom geschlossenen Vorkommensgebiet entfernt. In den USA bildet zurzeit eine kleine Population auf Santa Catalina den westlichsten Vorposten, eine im Kerr County in Texas den südöstlichsten.
Bevorzugte Lebensräume der Art sind aufgelockerte Eichenwälder und Eichen-Kiefern-Mischwälder. Die Art dringt auch entlang von vor allem mit Pappelarten bestandenen Flussläufen in semiaride Gebiete vor und besiedelt große Parks, Friedhöfe oder andere anthropogen gestaltete Landschaften, solange ausreichend Eicheln als Winternahrung zur Verfügung stehen. In den nördlichsten Verbreitungsgebieten brütet der Eichelspecht in reinen Koniferenbeständen, im Süden in tropischen Hartlaubgehölzen. Im südlichen Mittelamerika und in Kolumbien ist die Bindung an Eichen als Nahrungsbaum zwar ebenfalls vorhanden, aber nicht so ausschließlich wie im nördlichen Teil des Verbreitungsareals. Neben Eichen, von deren Früchten viele Populationen des Eichelspechtes sehr stark abhängen, muss ein optimales Habitat ein ausreichendes Angebot an Ameisen und anderen Insekten bereitstellen sowie tote Bäume oder zumindest abgestorbene starke Äste aufweisen, in die Nist- und Schlafhöhlen gezimmert werden können. Auch in Kolumbien, wo das ganze Jahr über Fluginsekten, Früchte und Baumsäfte zur Verfügung stehen, und die Früchte der einzigen dort vorkommenden Eichenart nur eine untergeordnete Bedeutung für die Ernährung der Art haben, sind Eichengehölze, die sogenannten Robledales, bevorzugte Lebensräume.[3]
Eichelspechte sind vor allem Brutvögel der Mittelgebirge und der montanen Zonen. In vielen Bereichen ihres Verbreitungsgebietes steigen sie bis zur natürlichen Verbreitungsgrenze ihrer Brut- und Nahrungsbäume auf, in Kolumbien bis über 3500 Meter.[3] Im südlichen Mittelamerika und in Kolumbien fehlt die Art unter 1500 Meter weitgehend. Nur in Teilen Kaliforniens, auf der Baja California sowie an den Südwestabhängen der Sierra Madre del Sur brüten Eichelspechte in tiefgelegenen, küstennahen Bereichen.
Eichelspechte sind während des gesamten Jahres territorial. Die Größe der einzelnen Territorien ist jedoch äußerst unterschiedlich. In günstigen Gebieten liegt sie unter 10 Hektar, in suboptimalen Regionen sind die Reviere um ein Vielfaches größer. Gegenüber Artgenossen verteidigt der gesamte Familienverband die Schlüsselstellen, das sind die Brut- und Schlafhöhlen, die Speicher sowie die Nahrungs- und Saftbäume. Neben Artgenossen werden auch direkte Höhlen- oder Nahrungskonkurrenten aus der Umgebung dieser Stellen vertrieben. Andere Spechtarten, Krähen, Eulen und Stare werden energisch während des gesamten Jahres attackiert, auch gegenüber den in seinem Lebensraum vorkommenden Hörnchen verhalten sich Eichelspechte aggressiv. Andere Vogelarten werden meist geduldet, auch wenn sie die gleichen Nahrungsressourcen nutzen. In Mittelamerika wurden häufig Gesellschaften von Quetzals, Tukanen und Eichelspechten beim Früchteverzehr beobachtet.
Die meisten Populationen des Eichelspechtes sind Standvögel. Nur wenn die Vorratsspeicher erschöpft sind, verlassen sie ihr Brutgebiet und streifen meist kleinräumig umher. Nur bei weiträumig schlechtem Eichelangebot sind auch Wanderungen über einige 100 Kilometer möglich. Solche Situationen können zu sogenannten Wanderjahren führen, in denen Familiengruppen weit umherstreifen, ohne zu brüten. Sie können dann auch in Gebieten angetroffen werden, in denen sie sonst fehlen.[4]
Nur eine in den Huachuca-Bergen im südöstlichen Arizona verbreitete Population hat ein davon abweichendes Verhalten entwickelt. Die Spechte dieser isolierten Region legen selbst bei einem großen Angebot an Eicheln keine Speicher an, sondern verwahren nur einige Eicheln in Rindenritzen oder sonstigen Spalten. Diese Vorräte sind bald aufgebraucht. Danach verlassen alle Eichelspechte das Gebiet und ziehen in die lockeren Eichenwälder der östlichen Sierra Madre in Mexiko. Im Frühjahr kehren sie in ihr angestammtes Brutgebiet zurück.[4]
Eichelspechte ernähren sich sowohl von animalischer als auch von vegetabiler Kost. Der vegetabile Anteil ist höher, obwohl Insekten bevorzugt werden, wenn sie denn zur Verfügung stehen.[5] Neben Ameisen, insbesondere schwärmenden Geschlechtstieren, werden unterschiedliche Schmetterlingsarten, Fliegen, Läuse und Zikaden sowie Käfer und Wanzen erbeutet; die quantitative Zusammensetzung variiert und hängt von der saisonalen und regionalen Verfügbarkeit der Beutetiere ab. Holzbewohnende Käferlarven spielen im Nahrungsspektrum der Art keine Rolle. Daneben erbeuten Eichelspechte gelegentlich kleine Eidechsen, Säugetiere, Jungvögel und Vogeleier.
Der vegetabile Nahrungsanteil besteht vor allem aus Eicheln unterschiedlicher Eichenarten, der in vielen Populationen mehr als die Hälfte der aufgenommenen Nahrungsenergie ausmacht. Daneben werden verschiedene Nüsse, insbesondere Mandeln und Walnüsse, Kiefernsamen sowie Obst, Beeren und Gräsersamen verzehrt. Im Spätwinter und zeitigen Frühjahr bilden Baumsäfte eine wichtige Nahrungsergänzung. Im Lebensraum des Eichelspechtes in Kolumbien kommt nur eine Eichenart, Quercus humboldtii, vor. Eicheln spielen dort deshalb auch keine überragende Rolle. Hier überwiegen das ganze Jahr über Insekten, Früchte und Baumsäfte; gelegentlich wird auch Blütennektar aufgenommen.[6]
Eichelspechte erbeuten ihre Insektennahrung vor allem im Fluge. Meist wird sie von einem Ansitz aus erspäht und in einem kurzen Ausfallsflug gefangen. Kleine Beutetiere werden sofort gefressen, größere zu einer geeigneten Schmiede getragen und dort bearbeitet. Baumbewohnende Insekten werden von der Stamm-, Ast- oder Blattoberfläche abgelesen, manchmal werden auch lose Rindenstücke abgelöst; auch in Rindenritzen und Holzspalten bohrt die Art nach sich verbergenden Beutetieren. Echte Hackarbeit wurde nur ganz selten festgestellt. Häufig halten sich die Spechtgruppen dabei im oberen Stamm und Kronenbereich auf; nur selten erscheinen Eichelspechte auf dem Boden. Die Früchtenahrung wird direkt vom Baum gepflückt, Eicheln meist einzeln. Baumsäfte gewinnt er durch Anbohren saftführender Stämme und Äste, wobei die Löcher, in denen sich der Baumsaft sammelt, unregelmäßig auf Stämmen und Ästen verteilt sind. Vor allem Eichenarten werden als Saftlieferanten genutzt. Fast alle Aktivitäten zur Nahrungsaufnahme vollziehen sich in der Gruppe; dabei sind laufend unterschiedlich getönte Wäke-Rufe zu hören; innerartliche Aggression besteht beim Nahrungserwerb kaum.
Fast alle Unterarten des Eichelspechtes betreiben eine intensive herbstliche Vorratshaltung. Bei einigen Populationen der Nominatform ist diese aus bisher nicht bekannten Gründen weniger ausgeprägt, bei den Vögeln der Unterart M. f. flavigula fehlt sie weitgehend. Charakteristisch für die Art ist das Anlegen besonderer Speicher, im Englischen granaries („Kornspeicher“) genannt, in denen tausende Eichelsamen gespeichert werden können. Als Speicherbäume kommen alle Arten mit dicker Rinde in Frage. Die Löcher sind dem zu speichernden Objekt genau angepasst; sie dringen nicht ins Kambium vor und schaden dem Baum nicht. Umfangreiche Speicher sind das Werk vieler Spechtgenerationen, denn jeder einzelne Eichelspecht hackt und bohrt in einem Herbst und Winter nur wenige Speicherlöcher. Die meisten Löcher liegen im Stammbereich, oft auch auf der Unterseite starker Seitenäste. Jede Spechtgruppe unterhält in ihrem Revier einen Hauptspeicher und einige Nebenspeicher. Außer Eicheln werden Nüsse und Kiefernsamen, gelegentlich auch Käfer aufbewahrt. Neben den Bruthöhlen sind die Speicher Zentren des Reviers; sie werden energisch von allen Familienmitgliedern verteidigt.
Wie einige andere Arten dieser Gattung leben Eichelspechte in sozialen Verbänden. Die Theorie, dass durch diese soziale Lebensweise ein Lebensraum, der nur beschränkte Ressourcen zur Verfügung stellt, bestmöglich ausgenutzt werden kann (habitat saturation), wird teilweise wieder in Frage gestellt, da Eichelspechte auch in Gegenden mit reichlichem Nahrungsangebot in Familiengruppen leben. Diese Gruppen bestehen aus 2 bis 15 Mitgliedern. Die Gruppen bestehen üblicherweise aus 1–4 männlichen Brütern, 1–2 weiblichen Brütern, wobei eines meist als Hauptbrüterin agiert, und 0–10 Helfern beiderlei Geschlechts. Die Helfer sind meist die Nachkommen aus letztjährigen Bruten. Weibliche Nebenbrüter legen ihre Eier in die Bruthöhle des Hauptweibchens, die diese jedoch bis zum eigenen Legebeginn aus der Höhle trägt, wo sie anschließend von den Familienmitgliedern verzehrt werden. Männliche Nebenbrüter kopulieren mit anderen Weibchen, selten jedoch mit dem Hauptweibchen. Kopulationen von Nebenbrütern werden oft von anderen Männchen, besonders aber dem Hauptmännchen gestört. Eine weitere vehemente innerartliche Aggression kann auftreten, wenn während der Brutzeit ein Hauptbrutpartner stirbt und durch einen anderen ersetzt wird. Dieser zerstört dann fast immer das Gelege oder tötet die Nestlinge. Auch dann, wenn außerhalb der Brutzeit alle männlichen oder weiblichen Brüter verschwinden oder umkommen und Artgenossen von außen diese Lücke zu schließen versuchen, kommt es zu intensiven, oft mehrwöchigen Auseinandersetzungen zwischen den verbliebenen Brütern und Helfern und den Eindringlingen.[7]
Außerhalb dieser reproduktiv bestimmten Situationen leben Eichelspechte in ihrem Familienverband kooperativ, jedoch mit gewisser Distanz zusammen. Die meisten Aktivitäten vollziehen sich im Verband, der andauernd in Stimmfühlung verbunden ist. Hierarchiekämpfe innerhalb einer Gruppe wurden nicht beobachtet.
Eichelspechte werden zum Ende des ersten Lebensjahres geschlechtsreif; etwas über 31 Prozent der Einjährigen beiderlei Geschlechts schreiten in diesem Alter zur ersten Brut. Im zweiten Lebensjahr sind drei Viertel aller Spechte Brüter. In Einzelfällen können jedoch nichtbrütende Helfer ein Alter von über 5 Jahren aufweisen.[8] Die Paarungssysteme in Eichelspechtgruppen sind variabel. Es kann ein Hauptpaar bestehen, das weitgehend monogam ist, oder ein Hauptbrüter unterschiedlichen Geschlechts, der sich mit den Brütern des anderen Geschlechtes verpaart. Es wird nur eine Nisthöhle gebaut, weibliche Nebenbrüterinnen legen ihre Eier ebenfalls in diese. Die Nisthöhle befindet sich meist hoch am Stamm oder einem starken Seitenast unterschiedlicher Baumarten; sie kann im Baum liegen, in dem sie auch die Speicher befinden, aber auch bis zu einem Kilometer von der Vorratskammer entfernt. Meist werden abgestorbene Bäume gewählt, zumindest aber vorgeschädigte Stellen ausgenutzt. Bei lebenden Bäumen werden solche mit weichem Holz, insbesondere Pappeln gewählt. Am Bau der Höhle beteiligen sich alle Gruppenmitglieder, die brütenden jedoch stärker als die Helfer. Die Nisthöhlen werden über mehrere Jahre benutzt, dennoch werden jedes Jahr neue gezimmert, sodass einer Eichelspechtgruppe fast immer ausreichend Nist- und Schlafhöhlen zur Verfügung stehen.
Die Legeperiode liegt in Oregon und Kalifornien im April und Mai, in Arizona etwas später; in den mittelamerikanischen Brutgebieten zwischen April und dem Beginn der Hurrikansaison im Juni. In Kolumbien brüten Eichelspechte im März und April. In den kalifornischen Küstengebieten schreiten Eichelspechte bei besonders guter Eichelernte im Spätsommer und Herbst zu einer zweiten Brut; in anderen Regionen werden bei Gelegeverlust zwar Zweitbruten innerhalb desselben Brutzyklus begonnen, regelmäßige, vom Hauptzyklus abgesetzte Zweitbruten wurden nur selten beobachtet.
Die Gelege sind je nach Anzahl der Zweitlegerinnen unterschiedlich groß; durchschnittlich umfassen sie 5 (4–9) reinweiße Eier. Sie werden 11 Tage hauptsächlich von den eierlegenden Weibchen und den brütenden Männchen bebrütet. Der Anteil der Helfer am Brutgeschäft ist gering. Nach dem Schlupf werden die Nestlinge von allen Gruppenmitgliedern betreut. In allen Aspekten der Fürsorge überwiegt der Anteil der eierlegenden Weibchen den der brütenden Männchen; jener der Helfer ist am geringsten, jedoch nicht unbeträchtlich. Nach durchschnittlich 32 Tagen fliegen die Jungspechte aus und werden noch längere Zeit von allen Gruppenmitgliedern mit Nahrung versorgt. Die Ausfliegerate beträgt im Mittel etwas über 60 Prozent; sie ist in großen Familienverbänden am größten.[9][10]
Der Eichelspecht ist ein Vertreter der Gattung Melanerpes, in der 24 meist mittelgroße Spechte zusammengefasst sind, deren Verbreitungsgebiet Nord-, Mittel- und Südamerika sowie einige der Karibischen Inseln umfasst. Mindestens acht dieser Arten leben dauernd in sozialen Verbänden. Innerhalb dieser Gattung bildet Melanerpes formicivorus (Swainson, 1827)[11] gemeinsam mit dem Blutgesichtspecht und dem Rotkopfspecht die Tribus Melanerpini.[12] Die Art zeigt eine weitgehend klinale geographische Variation in Bezug auf Färbung von Kehle, Brust und Wangen. Zusätzlich bestehen Unterschiede in der Gesamtlänge, in der relativen Schwanz- und der Schnabellänge. Anhand dieser Variablen gelten zurzeit sieben Unterarten als allgemein anerkannt.[13] Genetische Untersuchungen stehen noch aus.
Die Nominatform ist von Arizona und Neu-Mexiko südwärts bis zum Isthmus von Tehuantepec verbreitet. Individuen dieser Unterart und der nördlich und östlich von ihr lebenden Unterart M. f. bairdi Ridgway, 1881[14] sind die größten; die Kehlfärbung ist weitgehend weiß, ebenso das vordere Wangenfeld. Im Brustgefieder sind nur wenige rote Federn eingestreut. In den südwestlichen USA sind die beiden Gruppen durch die Mojave-Wüste getrennt.
Stark unterscheidet sich die isoliert auf der südlichen Baja California vorkommende Unterart M. f. angustifrons S. F. Baird, 1870[15], bei der die Iris eher einen bräunlichen Farbton aufweist, und deren Flügellänge von allen Unterarten die mit Abstand kleinste ist.
Die in den Bergländern Mittelamerikas voneinander isoliert lebenden Unterarten M. f. lineatus (Dickey & Van Rossem, 1927)[16] (Oaxaca und Chiapas südwärts bis Nicaragua), M. f. albeolus Todd, 1910[17] (Südliches Belize und Nordosten Guatemala) und M. f. striatipectus Ridgway, 1874[18] (Bergländer von Costa Rica und Bergregionen in Panama), ähneln einander in der Größe sehr, und sind auch in der Färbung nur geringfügig verschieden. Alle weisen einen relativ großen Anteil an roten Federn im schwarzen Brustgefieder auf.
M. f. striatipectus leitet zur südlichsten Unterart M. f. flavigula (Malherbe, 1849)[19] über, die isoliert in einigen Andenregionen Kolumbiens vorkommt. Bei diesen Vögeln ist das Gesichtsfeld gelb behaucht, die Kehle hingegen satt gelb. Bei flavigula tragen nur die Männchen eine in der Größe stark reduzierte rote Kopfplatte, während bei den Weibchen die Scheitelpartie schwarz ist. Zusammen mit angustifrons gehören die beiden letztgenannten Unterarten zu den kleinsten Vertretern dieser Art.[20]
Birdlife International listet den Eichelspecht in keiner Gefährdungsstufe.[21] Dieselbe Quelle beziffert die Gesamtpopulation nach einer Schätzung von 2003 mit etwas über 3 Millionen Individuen. In vielen Teilen seines Verbreitungsgebietes ist der Eichelspecht die häufigste Spechtart.
Der Eichelspecht (Melanerpes formicivorus) ist ein mittelgroßer Vertreter der Gattung Melanerpes innerhalb der Unterfamilie der Echten Spechte (Picinae). Die auffällige und nicht seltene Art ist vom Südwesten Washingtons südwärts bis ins nordwestliche Südamerika verbreitet. Wie einige andere Melanerpes-Arten leben auch Eichelspechte meist in Familiengruppen, in denen eine höchst differenzierte Sozialstruktur ausgebildet ist. Die geographische Variation ist groß: Es werden über zehn Unterarten beschrieben, von denen sieben allgemein anerkannt sind. Fast alle Unterarten sind Standvögel und betreiben eine intensive herbstliche Vorratshaltung.
The acorn woodpecker (Melanerpes formicivorus) is a medium-sized woodpecker, 21 cm (8.3 in) long, with an average weight of 85 g (3.0 oz).
The acorn woodpecker was formally described in 1827 by the English naturalist William John Swainson under the binomial name Picus formicivorus from a specimen collected in Mexico.[2] The specific epithet combines the Latin formica meaning "ant" with -vorus meaning "eating".[3] The type locality is Temascaltepec in Mexico.[4] The acorn woodpecker is one of 24 species now placed in the genus Melanerpes that was introduced by Swainson in 1832.[5][6] Within Melanerpes the acorn woodpecker is sister to a clade containing two South American species: the white woodpecker (Melanerpes candidus) and the white-fronted woodpecker (Melanerpes cactorum).[7]
Seven subspecies are recognised:[6]
The adult acorn woodpecker has a brownish-black head, back, wings and tail, white forehead, throat, belly and rump. The eyes are initially dark in fledglings, turning to white within a few months. There is a small part on the small of their backs where there are some greenish feathers. In most subspecies, adult males have a red cap starting at the forehead, whereas females have a black area between the forehead and the cap. The white neck, throat, and forehead patches are distinctive identifiers. When flying, they take a few flaps of their wings and drop a foot or so. White circles on their wings are visible when in flight. Acorn woodpeckers have a call that sounds almost like they are laughing.
Measurements:[8]
The acorn woodpecker's habitat is forested areas with oaks in the coastal areas and foothills of Oregon, California, and the southwestern United States, south through Central America to Colombia.[9] This species may occur at low elevations in the north of its range, but rarely below 1,000 m (3,300 ft) in Central America, and it breeds up to the timberline. Nests are excavated in a cavity in a dead tree or a dead part of a tree.
Acorn woodpeckers are cooperative breeders, living and breeding in family groups of up to 15 individuals. Field studies have shown that within the same population, groups range from monogamous pairs to polygynandrous breeding collectives consisting of coalitions of up to 8 males and 4 females, along with nonbreeding "helpers at the nest" that are offspring from prior breeding events. Regardless of composition, all breeder males (who are usually brothers or fathers and their sons) compete for matings with all breeder females (who are sisters or a mother and her daughter), the latter of which lay their eggs communally in the same nest cavity. There is considerable variability within and among populations, suggesting extraordinary social plasticity.[10] Cooperative breeding, defined as more than two birds taking care of nestlings in the nest, is a relatively rare evolutionary trait that is thought to occur in only nine percent of bird species.[11] Most cooperative breeding species have helpers at the nest, but acorn woodpeckers are unusual in exhibiting both helping at the nest and cooperative polygamy (polygynandry). It is generally believed that limited territories are a key driver of cooperative breeding behavior in birds, and in the case of the acorn woodpecker, the availability of acorn storage granaries (see Food and feeding) is a key limited resource.[12]
Breeding coalitions consist of up to eight cobreeding males and up to four joint-nesting females. However, most nests consist of only a single breeder female and 1 to 3 cobreeder males.[13] Nesting groups can also contain up to ten offspring helpers.[14] As mentioned above, the breeder males are often brothers, and the females are usually sisters. However, reproductive vacancies--formed when all the breeders of one sex die--are filled by unrelated birds from elsewhere, so Inbreeding is rare, despite the high degree of relatedness among most group members.[15]
In groups with more than one breeding female, the females put their eggs into a single nest cavity. A female usually destroys any eggs in the nest before she starts to lay. Once all the females start to lay, they stop removing eggs.[16] Although multiple paternity and maternity are common within groups containing multiple cobreeders, no extra-group paternity has been detected.[17]
Acorn woodpeckers, as their name implies, depend heavily on acorns for food. Acorns are such an important resource to the California populations that acorn woodpeckers may nest in the fall to take advantage of the fall acorn crop, a rare behavior in birds.[18] Acorns are stored in small holes drilled especially for this purpose in "granaries" or "storage trees"--usually snags, dead branches, utility poles, or wooden buildings. Storage holes--always in dead tissue such as bark or dead limbs--are used year after year, and granaries can consist of thousands of holes, each of which may be filled by an acorn in the autumn. Access to acorn crops influences the composition of acorn woodpecker communities. In one study in New Mexico, there were about 90% of non-breeding adults per social unit in 1976, a year of a poor acorn crop. The following year, 1977, there was a significant increase in acorn production and a correlating decrease in non-breeding adults per unit. [19]
Although acorns are an important back-up food resource, acorn woodpeckers primarily feed on insects, sap, and fruit. They can be seen sallying from tree limbs to catch insects, eating fruit and seeds, and drilling holes to drink sap.
The woodpeckers then collect acorns and find a hole that is just the right size for the acorn. As acorns dry out, they are moved to smaller holes and granary maintenance requires a significant amount of the bird's time. The acorns are visible, and a group defends its granary against potential cache robbers like Steller's jays and western scrub-jays.
In some more tropical parts of its range the acorn woodpecker does not construct a "granary tree", but instead stores acorns in natural holes and cracks in bark. If the acorn crop is poor and birds cannot find enough to store, the woodpeckers will move to other areas over the winter.
Male with "granary tree" full of acorns
Hoarded acorn
.jpg)
Three woodpeckers in California. One breaks open an acorn.
Acorn woodpeckers, like many other species, are threatened by habitat loss and degradation. Competition for nest cavities by non-native species is an ongoing threat in urbanized areas. Conservation of this species is dependent on the maintenance of functional ecosystems that provide the full range of resources upon which the species depends. These include mature forests with oaks capable of producing large mast crops and places for the woodpeckers to nest, roost, and store mast. Residents are encouraged to preserve mature oak and pine-oak stands of trees and to provide dead limbs and snags for nesting, roosting, and granary sites to help preserve the acorn woodpecker's population.
Walter Lantz is believed to have patterned the call of his cartoon character Woody Woodpecker on that of the acorn woodpecker, while patterning his appearance on that of the pileated woodpecker, which has a prominent crest.[20]
_female_Copan.jpg)
Female M. f. lineatus, Honduras The acorn woodpecker (Melanerpes formicivorus) is a medium-sized woodpecker, 21 cm (8.3 in) long, with an average weight of 85 g (3.0 oz).
La Glanpego (Melanerpes formicivorus) estas mezgranda melanerpo, tio estas birdo de la familio de Pegedoj, kiu loĝas el sudokcidenta Usono kaj ĝis Centrameriko.
Temas pri pego 21 cm longa kun mezaveraĝa pezo de 85 g. Plenkreskuloj havas nigrajn kapon, dorson, supran bruston, flugilojn kaj voston kaj blankajn frunton, gorĝon, ventron kaj pugon. La okuloj estas blankaj kaj la beko estas nigra. La plenkreska masklo havas ruĝan kronon, kiu komencas ĉe la blanka frunto, dum inoj havas nigran areon inter la frunto kaj la krono, tio estas ili havas nur duonkronon ruĝan. Ĉiukaze la blankaj fruntoj kaj larĝa gorĝo, ĉirkaŭitaj de nigraj areoj, estas klare distingilaj identigmakuloj.
La reprodukta habitato estas arbaraj areoj kun kverkoj de la montetoj de la marborda Kalifornio kaj aliaj areoj de sudokcidenta Usono suden tra Meksiko kaj Centrameriko ĝis nordokcidenta Kolombio. Tiu specio povas loĝi altaĵojn en la nordo de sia teritorio, sed rare sub 1000m en Centrameriko, kaj ĝi reproduktiĝas ĝis la lignolimo. La reprodukta paro elfosas neston en granda kavaĵo en morta arbo aŭ morta parto de arbo. Grupo de plenkreskuloj povas partopreni en la nest-agado: kampostudoj montris, ke la reproduktaj grupoj ampleksas el monogamaj paroj al reprodukta kolektivo de ĝis 7 maskloj kaj 3 inoj, plus ĝis 10 nereproduktantaj helpantoj ĉe reproduktado. Oni trovis idojn de multobla patreco.[1]
La Glanpego estas viglaj proviz-stokistoj. Reproduktantaj grupoj stokas glanojn kaj kreas glanujon traborante truojn en morta arbo aŭ morta branĉo de vivanta arbo, kaj ŝtopante glanojn en ili. La glanoj estas videblaj, kaj la grupo defendos la arbon kontraŭ eventualaj glanoŝtelistoj. Tiu rimarkinda kaj distinga kutimo nomigas la specion kiel Glanpego.
La glanoj reprezentas signifan parton de ties dieto; ili manĝas ankaŭ insektojn, elplukante ilin el la arboŝelo (kiel aliaj pegedoj) aŭ kaptante ilin dumfluge, kaj krome frukton, semojn kaj foje arboŝevon.
Tiu birdospecio estas konstanta loĝanto tra sia teritorio. Ili povas translokiĝi al alia areo, se ne estas facile disponeblaj glanoj. Ĝi estas nemigranta kaj tre sociebla.
Estas agnoskitaj la jenaj subspecioj:
La Glanpego (Melanerpes formicivorus) estas mezgranda melanerpo, tio estas birdo de la familio de Pegedoj, kiu loĝas el sudokcidenta Usono kaj ĝis Centrameriko.
El carpintero bellotero (Melanerpes formicivorus[1]) es un pájaro carpintero de tamaño medio. Habitan en robledales, desde el sur de los Estados Unidos hasta Colombia. Anidan en árboles o ramas muertas, en grandes cavidades excavadas por la pareja. En la cría suelen participar varios individuos adultos: los estudios de campo muestran que estos grupos pueden estar constituidos por parejas criadoras monógamas o hasta por colectivos de siete machos y tres hembras (con más de 10 ayudantes no criadores). Es una especie residente permanente. Pero, si no hay bellotas disponibles pueden emigrar a otra área. Se encuentra desde Canadá hasta Colombia.[2]
Los adultos tienen la cabeza, el dorso, las alas y la cola negras; la frente, la garganta, el vientre y el manto, blancos. Sus ojos son también blancos. Los machos adultos tienen el píleo completamente rojo mientras que las hembras presentan una franja negra entre la frente blanca y el píleo rojo.
Los grupos criadores crean auténticas despensas en las que acumulan bellotas: excavan agujeros en los árboles muertos y las almacenan allí. Estas bellotas quedan a la vista, así que el grupo va a defender el árbol de posibles robos. Las bellotas constituyen una parte importante de su dieta; también comen insectos que capturan de la corteza de los árboles o que atrapan en vuelo, además de frutos, semillas y, a veces, savia. Anualmente pueden cavar 60,000 agujeros en un árbol con bellotas e incluso lo introducen en distintos para cubrirlo completo así evitarán que otro individuo se los hurte.
El carpintero bellotero (Melanerpes formicivorus) es un pájaro carpintero de tamaño medio. Habitan en robledales, desde el sur de los Estados Unidos hasta Colombia. Anidan en árboles o ramas muertas, en grandes cavidades excavadas por la pareja. En la cría suelen participar varios individuos adultos: los estudios de campo muestran que estos grupos pueden estar constituidos por parejas criadoras monógamas o hasta por colectivos de siete machos y tres hembras (con más de 10 ayudantes no criadores). Es una especie residente permanente. Pero, si no hay bellotas disponibles pueden emigrar a otra área. Se encuentra desde Canadá hasta Colombia.
Melanerpes formicivorus Melanerpes generoko animalia da. Hegaztien barruko Picidae familian sailkatua dago.
Melanerpes formicivorus Melanerpes generoko animalia da. Hegaztien barruko Picidae familian sailkatua dago.
Melanerpes formicivorus
Le Pic glandivore (Melanerpes formicivorus) est une espèce d’oiseaux de la famille des Picidae.
Cet oiseau a un plumage essentiellement noir (tour du bec, dos et ailes notamment) et blanc (gorge et croupion en particulier) à l'exception d'une calotte rouge. Le dessous du corps est blanc rayé de noir. Un léger dimorphisme sexuel existe : le front est blanc chez le mâle et noir chez la femelle.
Cette espèce vit du littoral de la Californie au sud-ouest des États-Unis jusqu'en Colombie : Costa Rica...
Cet oiseau se reproduit dans les chênaies des collines côtières mais aussi dans les forêts de montagne au-delà de 1 500 m d'altitude. Il peut s'alimenter dans les prés bordant les milieux forestiers.
Les couples reproducteurs excavent un nid dans une grande cavité dans un arbre mort ou une partie morte d'un arbre. Un groupe d'adultes peut participer aux activités de nidification: des études en milieu naturel ont montré que les groupes reproducteurs vont de paires monogames aux groupes reproducteurs collectifs de sept mâles et trois femelles avec jusqu'à 10 manœuvres associés. Les jeunes d'une même couvée peuvent être issus de paternités multiples.
Cet oiseau consomme des glands, des fruits et des insectes. Il fait des réserves dans les crevasses des arbres et dans les cavités qu'il y creuse[1],[2],[3].
Les pics glandivores, comme leur nom l'indique, dépendent fortement des glands pour se nourrir. Les glands sont une ressource si importante pour les populations californiennes que les pics à glands peuvent nicher à l'automne pour profiter de la récolte de glands, un comportement rare chez les oiseaux[4].
Walter Lantz se serait inspiré du cri du pic glandivore pour créer celui de son personnage de dessin animé Woody Woodpecker, tout en modelant son apparence sur celle du grand pic, à la crête caractéristique[5].
D'après la classification de référence (version 5.2, 2015) du Congrès ornithologique international, cette espèce est constituée des sept sous-espèces suivantes (ordre phylogénique) :
Melanerpes formicivorus
Le Pic glandivore (Melanerpes formicivorus) est une espèce d’oiseaux de la famille des Picidae.
Il picchio delle ghiande (Melanerpes formicivorus (Swainson, 1827)) è un uccello appartenente alla famiglia Picidae.[2]
Il picchio delle ghiande è lungo 23 centimetri, pesa tra i 65 e i 90 grammi e ha un'apertura alare di circa 13-15 centimetri. Il piumaggio è di un bel nero brillante sul dorso, sulle ali, sulla coda e sulla maschera facciale. Il capo è sormontato da una vistosa corona rossa; a partire dalla parte inferiore del viso fino all'attaccatura della coda, il piumaggio è bianco più o meno striato da chiazze nere. Sulla gola c'è una zona, di solito una sorta di semicollare, con piume dalla punta gialla o rossa chiara. Il becco è conico, robusto leggermente più lungo della media degli altri Picidi, le zampe sono grigie e forti, gli occhi piccoli e bianchi.
Lo si incontra nell'America occidentale, dallo Stato dell'Oregon negli Stati Uniti, sempre lungo la costa pacifica, attraverso Messico, stati del Centro America, fino alla zona andina della Colombia.
Vive quasi esclusivamente nelle foreste di pini e di querce; è stato avvistato in foreste di abeti, di sequoie e di altre latifoglie, ma solo se nelle vicinanze sono presenti querce. In città è presente solo nei grandi parchi dove c'è abbondanza di querce.
Il picchio delle ghiande è un uccello sociale e stanziale che vive in gruppi composti da tre fino a dodici individui. Ognuno di questi ha il compito di difendere il territorio che può essere anche molto vasto, comprendendo la dispensa comune, le zone di nidificazione e le zone di procacciamento del cibo; oltre a ciò ciascuno contribuisce alla costruzione dei nidi e all'allevamento dei piccoli. Nelle zone in cui le variazioni climatiche sono più consistenti, i picchi delle ghiande possono percorrere brevi viaggi di migrazione.
Il comportamento nutritivo di questa specie è piuttosto complesso. I membri del gruppo scelgono un "albero granaio" sul quale praticano migliaia di fori. In ognuno di questi verranno incastrate e conservate le ghiande che costituiscono circa la metà della dieta giornaliera di questo picchio. Si è stimato che un'unità sociale riesce a conservare fino a 50000 ghiande in un solo albero. Il "granaio" verrà utilizzato soprattutto durante l'inverno fino alla primavera successiva. Oltre alle ghiande, si cibano di linfa, semi (di pino in particolare) e frutti. La dieta dei piccoli invece è quasi esclusivamente insettivora, le formiche in modo particolare (da qui il formicivorus della specie) arrecano le proteine necessarie alla loro crescita.
Il comportamento riproduttivo di questa specie è molto complesso, seppur mancante della fase di corteggiamento. In un gruppo sono presenti circa 7-9 maschi e 1-3 femmine. I maschi competono tra loro per la riproduzione, interrompendo spesso la copula dei rivali con attacchi mirati. Se nel gruppo le femmine sono più di una, allora anche loro competono per l'accoppiamento e la deposizione delle uova, distruggendo quelle deposte dalle rivali. Quando però si stabilisce una certa gerarchia per la deposizione, una sequenza che viene considerata corretta dal gruppo, allora vengono deposte solitamente 5-6 uova bianche. Il periodo d'incubazione è di undici giorni. Dopo la schiusa, tutto il gruppo si prende cura dei piccoli fino a quando lasceranno il nido a circa 32 giorni dalla nascita. Questo comportamento che coinvolge tutti gli elementi del gruppo, sia prima sia dopo la deposizione delle uova, è chiamato "poliginandria".
Il nido è una cavità di un albero, il cui interno è ricoperto di foglie e erba fresche, a volte vicino all'"albero granaio".
Melanerpes formicivorus comprende 7 sottospecie:[2]
Il picchio delle ghiande (Melanerpes formicivorus (Swainson, 1827)) è un uccello appartenente alla famiglia Picidae.
Melanerpes formicivorus species avium est generis Melanerpes, familiae Picidarum, ordinis Piciformium. Habitat Americam septentrionalem, regionem orientalem Civitatum Foederatarum Americae etiamque Americam centralem et partem septrentionalem Americae meridionalis.
Melanerpes formicivorus species avium est generis Melanerpes, familiae Picidarum, ordinis Piciformium. Habitat Americam septentrionalem, regionem orientalem Civitatum Foederatarum Americae etiamque Americam centralem et partem septrentionalem Americae meridionalis.
De eikelspecht (Melanerpes formicivorus) is een vogel uit de familie spechten (Picidae).
Het verenkleed, dat bij beide geslachten gelijk is, is glanzend zwart met een rode kruin en witte onderdelen. Het vrouwtje heeft bovendien een zwarte voorkruin. De vogel heeft een vrij korte snavel. De lichaamslengte bedraagt 23 cm en het gewicht 65 tot 90 gram.
Het hoofdvoedsel van deze vogels bestaat uit eikels, waarvan ze een voorraad aanleggen, die ze stoppen in gaten in bomen, schuttingen en houten gebouwen. Ze eten ook zaden, boomsappen en vruchten. De jongen worden gevoerd met insecten. Deze vogels zijn erg territoriaal en verdedigen het territorium en nest tegen indringers. Dat is begrijpelijk, want in het territorium bevinden zich de foerageerplaatsen, sapbomen, de voedselvoorraad en de roest- en nestplaatsen.
Deze standvogel komt voor van westelijk Noord-Amerika tot Colombia in eikenbossen en gemengde eiken-naaldhoutbossen.
De soort telt 7 ondersoorten:
De eikelspecht heeft een groot verspreidingsgebied en daardoor alleen al is de kans op de status kwetsbaar (voor uitsterven) uiterst gering. De grootte van de populatie is niet gekwantificeerd, maar de aantallen nemen toe. Om deze redenen staat de eikelspecht als niet bedreigd op de Rode Lijst van de IUCN.[1]
Bronnen, noten en/of referenties
Multimedia w Wikimedia Commons Dzięciur żołędziowy (Melanerpes formicivorus) – gatunek ptaka z rodzaju Melanerpes, zaliczanego do rodziny dzięciołowatych. Występuje w południowo-zachodniej Ameryce Północnej, po Meksyk aż do południowoamerykańskiej Kolumbii.
Dorosły dzięciur żołędziowy ma ciemnobrązową głowę, kark, skrzydła i ogon, białe czoło, podgardle, część brzuszną i kuper. Oczy mają białe tęczówki. Na niewielkim fragmencie grzbietu występuje parę zielonych piór. Dojrzały samiec posiada na czole czerwoną czapeczkę, która ciągnie się w stronę grzbietu. Pomiędzy potylicą a okolicami dzioba u samicy występują pas czarnych piór. W trakcie lotu łopoczą skrzydłami ze spuszczonymi nogami. Widać wtedy białe koła na skrzydłach. Ich odgłosy przypominają śmiech.
Ptaki żyją w stadkach złożonych z 20 osobników. Razem żywią się nie tylko owadami, ale i żołędziami i innymi nasionami. Zbierają je i gromadzą wspólnie w schowkach wykutych w pniach drzewach. Ptaki tworzące grupę bronią dostępu przed obcymi osobnikami do drzewa, które jest spichlerzem.
Rozród u dzięciurów żołędziowych jest osobliwy. Przeważnie tylko dwie samice wchodzące w skład grupy składają jaja do wspólnej dziupli. Z reguły pierwsze, a czasami i drugie złożone jajo jest rozbijane i pożerane wspólnie przez całą grupę. Wysiadywanie rozpoczyna się dopiero wtedy, gdy dwie samice prawie jednocześnie złożą jaja. Gdy pisklęta się wyklują wszyscy uczestnicy grupy karmią je owadami. Dowiedziono, że około 10% złożonych jaj źle się rozwija, a tylko z 20% rozwijają się pisklęta, które później osiągają zdolność do lotu.
W okresie nadmiaru żołędzi i innych nasion pokarmu starcza dla dorosłych ptaków, a produkcja jaj jest ponoszona niskim kosztem. Natomiast karmienie piskląt owadami wymaga bardzo efektywnych łowów, co wymusza współpracę w żywieniu. Osobnik, który karmi obce pisklę w kolejnym sezonie ma większe szanse na przekazanie genów następnemu pokoleniu. Co ciekawe, opisane wyżej zachowanie charakteryzuje populację z południowej Kalifornii. Już w Arizonie dzięcioły w trakcie rozrodu nie korzystają z pomocników robiąc tylko niewielkie zapasy nasion, a na zimę wędrując do Meksyku.
Dzięciur żołędziowy (Melanerpes formicivorus) – gatunek ptaka z rodzaju Melanerpes, zaliczanego do rodziny dzięciołowatych. Występuje w południowo-zachodniej Ameryce Północnej, po Meksyk aż do południowoamerykańskiej Kolumbii.
Samlarspett[2] (Melanerpes formicivorus) är en fågel i familjen hackspettar inom ordningen hackspettartade fåglar.[3]
Samlarspett delas in i sju underarter i två grupper:[3]
Arten har ett stort utbredningsområde och en stor population, och tros öka i antal.[1] Utifrån dessa kriterier kategoriserar IUCN arten som livskraftig (LC).[1]
Wikimedia Commons har media som rör samlarspett.
Wikispecies har information om Melanerpes formicivorus.
Samlarspett (Melanerpes formicivorus) är en fågel i familjen hackspettar inom ordningen hackspettartade fåglar.
Доросла особина має бурувато-чорну голову, спину, крила і хвіст та живіт. Очі білі. Існує невелика частина спини де можливе зелене пір'я. Дорослий самець має червону «шапочку», яка починається з лоба, в той час, як у самки між лобом та «шапкою» існує чорне пір'я. Розмір дорослого птаха близько 20 см при вазі 85 г.
Віддають перевагу лісовим масивам з присутністю дубів. Зустрічаються на пагорбах прибережних районів Каліфорнії, на південному заході Сполучених Штатів, Південній Колумбії. Цей вид може проживати на низьких висотах північної частини свого ареалу, але рідко нижче ніж 1000 м у Південній Америці.
Характерною особливістю цього дятла є його спосіб заготівлі жолудів на зиму. Птахи видовбують отвори в стовбурах дерев і складають туди жолуді. Трапляються випадки, коли дятли створювали отвори у телеграфних стовпах, в стінах дерев'яних будинків. В одній жовтій сосні було нараховано 60 тис. отворів з жолудями. Крім жолудів раціон цих птахів складають комахи, горіхи і плоди.
Гіла чорновола живуть групами-сім'ями від трьох до дванадцяти особин. Кожна така група-сім'я має спільну територію, в межах якої знаходяться комірки з жолудями, місця гніздування та збору їжі. В захисті своєї території беруть участь всі дорослі члени сім'ї. Вони ж беруть участь у створені запасів та подальшому їх використанню.
У Каліфорнії період розмноження приходить у травні-липні. В період розмноження від одного до семи самців спарюються з одною — трьома самками, при цьому вони не розбиваються на пари. Самки відкладають яйця у одне спільне гніздо, де позмінно висиджують пташенят, як у висиджуванні так і в подальшому догляді за пташенятами беруть участь усі члени зграї.
Гніздяться у дуплах мертвих і живих дерев, які використовуються неодноразово, а протягом багатьох років. Самики відкладають 5 яєць які висиджують протягом від 11-14 днів. Пташенята залишають гніздо і відправляються у перший політ приблизно через 30-32 днів після вилуплення. У догляді за пташенятами можуть брати участь і не статевозрілі особини які були народжені раніше.
Це незавершена стаття з орнітології.Melanerpes formicivorus là một loài chim trong họ Picidae.[1]
Bài viết liên quan đến bộ Gõ kiến này vẫn còn sơ khai. Bạn có thể giúp Wikipedia bằng cách mở rộng nội dung để bài được hoàn chỉnh hơn. Melanerpes formicivorus (Swainson, 1832)
Ареал
Муравьиный меланерпес[1], или муравьиный дятел[1] или желудёвый дятел[2] (лат. Melanerpes formicivorus) — птица из рода дятлов-меланерпесов. Известен своей особенностью создавать своеобразные «кладовые», запасая жёлуди, размещая их по одному в отверстия, выдолбленные в стволах деревьев.
Размеры взрослой птицы около 20 см при среднем весе около 85 г. Взрослая птица имеет чёрную голову, спину, крылья и хвост; белый лоб, горло, живот. Глаза белые. Взрослый самец имеет красную «шапочку», которая начинается на лбу, тогда как самки отличаются наличием чёрной области между лбом и «шапочкой».
Ареал разорванный, состоит из нескольких крупных и множества мелких участков в Северной, Центральной и Южной Америке. На северо-западе гнездится вдоль тихоокеанского побережья от северо-западного Орегона к югу до Калифорнийского залива. Наиболее крупный участок находится в промежутке между восточной Аризоной и западным Нью-Мексико на севере, и западной Панамой и северной Колумбией на юге.
Характерной особенностью поведения муравьиных дятлов является создание ими «кладовых»[3]. Птицы во множестве запасают жёлуди, размещая их по одному в отверстия, выдолбленные ими в стволах деревьев, а порой даже деревянных телеграфных столбов, или в стене бревенчатого дома. В одной жёлтой сосне было обнаружено до 60 тыс. спрятанных таким образом жёлудей. Подобные запасы используются птицами в зимнее время[2]. Кроме желудей, рацион дятлов включает орехи, насекомых и плоды, которые они также иногда могут запасать впрок.
Муравьиные дятлы живут коммунами-семьями расширенного состава численностью от 3 до 12 особей. Каждая такая коммуна удерживает общую территорию, в границах которой находятся кладовые, места гнездования и сбора корма. В защите данной территории принимают участие все члены группы. Они же участвуют в запасании желудей и потом же коллективно используют свои запасы[3].
Обычно в группе насчитывается 1—7 самцов и 1—3 самки. С приходом брачного периода птицы в группе не разбиваются на пары. Все самки откладывают яйца в одно общее гнездо. В насиживании кладки и в последующем выкармливании птенцов принимают участие все члены группы. Впрочем, в отдельные годы и в отдельных местах встречаются и пары птиц, ведущих типично моногамный образ жизни, являющийся временным явлением.
Муравьиный меланерпес, или муравьиный дятел или желудёвый дятел (лат. Melanerpes formicivorus) — птица из рода дятлов-меланерпесов. Известен своей особенностью создавать своеобразные «кладовые», запасая жёлуди, размещая их по одному в отверстия, выдолбленные в стволах деревьев.
ドングリキツツキ（団栗啄木鳥、学名:Melanerpes formicivorus）は、キツツキ目キツツキ科の鳥。
全長20cm。
森林に生息し、群れで縄張りを構えて生活する。
枯れ木に大量の穴をあけ、その中に餌であるドングリを一個ずつ貯蔵する習性をもつ。そのほか、昆虫類や果実も採食する。
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