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Violet-green swallows often rest on exposed perches such as tree branches and telephone wires. They fly at various heights and can be seen swooping down to skim the surface of ponds and lakes, flying at greater heights and beating their wings more rapidly than other swallows. While the species is extremely social and nests in colonies of up to 25 pairs, with some colonies having over twenty couples in a single tree, they are also capable of nesting solitarily. In addition, they are very social with members of other species of swallows and will often forage in interspecies groups of from 3 to over 50 individuals.
The IUCN Red List currently places T. thalassina in the category of “Least Concern.” This classification is due largely to the violet-green’s extensive range and to its ability to nest in both remote and urban locations, which creates a lessened impact from human development. While there is little research on the benefits of human efforts to assist with nesting, it has been observed that nest boxes have been helping these birds in different regions of their range. The National Audubon Society, however, states that violet-green swallows are “Climate Threatened” and provides maps and projections of how climate change might affect this species.
For nesting habitats, violet-green swallows occupy open or broken deciduous, coniferous, and mixed woodlands, mainly preferring trees in open areas, as well as cliffs, buildings, and other manmade structures. They sustain themselves on a diet of insects, primarily tree dwelling flying insects. Peregrine falcons and merlins are two of their biggest predatory threats. There is a significant danger of habitat destruction confronting these birds, but their numbers are fairly abundant and their habitat range is fairly large. There is some evidence of this species interacting with Western bluebirds in a commensalist manner, assisting with the rearing of young bluebirds and then using the bluebird nest as their own.
The habitat of the violet-green swallow is widespread when foraging. While breeding, they will roost in open deciduous, coniferous, and mixed woodlands, including ponderosa pine, Monterey pine, and quaking aspen. In the southern part of the range, they live most commonly at elevations of 2,000 to 3,500 feet, although they also nest in wooded canyons. Farther north, they breed and nest at lower elevations. When nesting, violet-green swallows can be found in open woodlands, mountains, and urban settings. While migrating, they will roost in semi-open areas, such as forests, canyon walls, or on the ground if no elevated spots are available.
Violet-green swallows typically will produce one brood per mating season, although second broods occasionally occur. The eggs have an incubation period of 13-15 days and the fairly helpless hatchlings have pale pink skin with wisps of creamy or grayish down on their backs, eyes yet to be opened, and a distinct creamy-whitish gape. At day 5, their skin darkens and their feather follicles begin to appear. At day 7, vocalizations begin to occur as they make their first ‘peep’. Between days 8-9, their eyes begin to open, their feather remiges begin to break through the sheaths, and finally the young begin to defecate in specific nest spots. At day 10, the nestlings are finally making double note noises and white feathers are appearing along the sides of their bodies. By day 16, the young have stopped gaping their mouths, their primary feathers are one inch long, their sides are covered with white silky feathers and their backs are covered in black fur. By day 18, the bird looks like an adult, with the only distinction being their protruding abdomen, which will begin to reduce in a few days. By day 22, the bird has full-length wing and tail feathers and is almost being completely mature. It will most likely fledge by day 24 or 25 and will lose its dependency on adults by day 27 or 28. Although there is limited information on the lifespan of violet-green swallows, the oldest known male was recorded to be over 9 years old.
The violet-green swallow (Tachycineta thalassina) is a small songbird in the Hirundinidae family. They are about 12 cm in length, with a wingspan of 27 cm and a weight of 14 g (All About Birds 2016). They are an iridescent violet-green on the crown, nape, and back, white on the underside, with white also on the sides of their heads. T. thalassina is native to Western North America, ranging from Alaska to Mexico, and is usually found in open woodlands, mountains, and various urban settings, where they can be observed flocking with others of their kind or with a variety of swallow species (Seattle Audubon 2016). The swallows feed mainly on flying insects, including flies, bees, true bugs, and beetles, which are caught in flight at different heights. They feed both independently and in small flocks, flying low over fields or water or circling and swooping from significant heights, often foraging at higher altitudes than other swallows (Brown, Knott, and Damrose 2011). They begin nesting in the spring, building their nests with twigs, grass, straw, and feathers. Eggs will be laid one per day until the clutch of 4-6 white eggs is finished, and females will then incubate the eggs for 14 to 15 days. After the eggs hatch, the adult female and male birds will both take part in feeding the young, and will continue to feed them for a short time after the young leave the nest, which occurs 23-24 days after hatching (Seattle Audubon 2016).
Like most other swallows, the violet-green swallow is an insectivore, which makes them heterotrophic and secondary consumers. Since they hunt primarily in flight, their diet is made up of flying insects such as bees and flies, although they have been known to consume ants and spiders as well. As with most other birds of similar size, the violet green swallow has few predators; only small birds of prey such as falcons and merlins are able to catch these agile flyers. Since these predators are relatively few in number, violet-green swallows occupy a comfortable niche in their food web, feeding on plentiful insects without fear of terrestrial predators. Even house cats pose little threat to violet-greens because they rarely stop to land and when they do it is generally in trees, on rooftops, or on telephone wires and almost never on the ground.
The violet-green swallow (Tachycineta thalassina) is a small North American passerine bird in the swallow family. These aerial insectivores are distributed along the west coast from Alaska to Mexico, extending as far east as Montana and Texas. With an appearance very similar to the tree swallow, these individuals can be identified by the white rump side-patches that appear to separate their green back and purple tail. Violet-green swallows are secondary cavity nesters, found in a number of habitats including deciduous and coniferous forest. In addition to nesting in tree holes within these habitats, they are also widely observed nesting in the cracks of large cliffs.[2]
The distinct body form of swallows distinguishes them from other passerine birds. Their long pointed wings and slim, streamlined body evolved to catch insects while in flight. The body of the violet-green swallow is no exception. With an average body length of 5¼ in. (13 cm), the violet-green swallow is slightly shorter and appears more compact in flight compared to other members of the family Hirundinidae. The violet-green swallow most closely resembles the North American tree swallow, but can be distinguished by its shorter wings and colouration.[2]
The violet-green swallow gets its name from the colouration on its back and rump. The species is best identified by the glossy green on the top of the head and back as well as hints of purple on the nape, rump and upper tail. Below the green back, the remainder of the wing is a grayish-bronze. Similar to other swallows, T. thalassina is white below, but differs in that the white continues onto rump side-patches that almost meet at the base of the tail. These white rump side-patches sometimes look like one continuous stripe when in flight. White also extends onto the cheeks, partially surrounding the eye.[2] The notch in the tail of the violet-green swallow is slightly shallower than that of the tree swallow, but deeper than the relatively flat tail of the cliff swallow.
Violet-green swallows exhibit very little sexual dimorphism, with adult males simply showing brighter colours than adult females. Additionally, the white cheeks are not as prominent and the head is more bronze than green on the female. Juveniles are not as easily identifiable compared to adults due to their dull colouration. Similar to other juvenile swallows, especially the tree swallow, the juvenile violet-green swallow is white below and grayish-brown above. However, the more gradual change in colour and visible (but slightly reduced) white cheek patches can help identify juvenile individuals of the species.[2]
The swallows have been well studied ecologically, but only recently has their phylogeny been thoroughly researched.[3][4][5][6] Swallows are passerine birds grouped within the family Hirundinidae. The family Hirundinidae is split into two subfamilies: Pseudochelidoninae, which contains two species of river martins, and Hirundininae, comprising all other martins and swallows. The 82 species within the subfamily Hirundininae are further classified into three groupings: the mud nesters, basal relicts and core martins, with the violet-green swallow falling into the last group.[5] Violet-green swallows are one of 9 species of New World tree swallows within the genus Tachycineta.[4][6] This genus is a monophyletic group and is considered the sister taxa of all other New World swallows.[3]
Violet-green swallows are important members of the Tachycineta clade due to their large geographic range and because they are one of 2 species that breed within North America. It is generally agreed that Tachycineta is split into a North and a South American clade, but the phylogenetic placement within the genus depends on the type of analysis used. The violet-green swallow is a member of the North American grouping, along with T. bicolor (the North American tree swallow), T. euchrysea (the golden swallow of Hispaniola and Jamaica) and T. cyaneoviridis (the Bahama swallow).[3][4][6] A mitochondrial genome analysis has placed T. thalassina as a sister taxon of the Caribbean swallows, T. euchrysea and T. cyaneoviridis, with all 3 species forming a sister clade to T. bicolor.[3][4] Nuclear genome analyses and a consensus of both methods have reorganized this North American clade, alternating the closest sister taxon of T. thalassina between T. cyaneoviridis and T. euchrysea.[6] Nonetheless, the taxonomy of the violet-green swallow is well understood up to the genus level, after which some uncertainty surrounds the placement of T. thalassina within the North American clade of the genus Tachycineta.
Violet-green swallows are divided into three subspecies, T. t. thalassina, T. t. brachyptera and T. t. lepida differing in breeding ranges and wing length. T. t. thalassina has slightly longer wings and has been known to breed as far north as Alaska, while the shorter winged T. t. brachyptera breeds further south in California and Mexico.[2][7] Not all of the literature agrees upon T. t. lepida as a third subspecies, and little information is available to help distinguish it from other subspecies.
Hybridization has been known to occur among the swallows, with a few cases involving violet-green swallows being reported. Breeding between violet-green swallows and both tree and barn swallows has been recorded on separate occasions, but resulting offspring were not observed. In 2000, the strange plumage of a swallow seen in British Columbia, Canada, suggested the possible successful hybridization of a violet-green and a cliff swallow.[8] Nonetheless, these observations are rare, which accounts for the minimal research into swallow hybridization.
The type of habitat occupied by violet-green swallows varies depending on their geographical location and elevation. Across their range, these birds can be found in deciduous, coniferous and mixed forests, as well as within canyons and in close proximity to large cliffs.[2][9] Breeding and non-breeding habitats do not differ much except that breeding habitat is usually at lower elevations. Violet-green swallows have also been observed nesting around buildings in more settled areas.[2]
Violet-green swallows are a predominantly western species, with the rare sighting of individuals in eastern North America. The distribution of the species can be divided on the basis of the recognized subspecies, but the entire range spans from central Alaska down to Mexico. Longitudinally, the range borders the west coast of Alaska, British Columbia and the United States, and extends eastward into southwestern Alberta, Montana, the Dakotas and Texas. The breeding range spans almost the entire distribution, while the winter range is restricted to Mexico.[2][10]
There are many knowledge gaps surrounding the vocalization behaviour of violet-green swallows. These gaps include vocalizations made during early development, alarm calls and the daily pattern of calls. The little information available suggests two main classes of vocalizations, the chee-chee calls and twitter calls.[11]
This call is most commonly heard when one violet-green swallow interacts with another swallow, either during foraging, in-flight chases or when approaching a nesting site. Flocks of swallows have been recorded making chee-chee calls, suggesting its use in social cohesion. Juveniles have also been observed making this vocalization when waiting to be fed by an adult, implying that it plays a role in parent-juvenile recognition.[11]
Observations of violet-green swallows making twitter calls typically associate the vocalization with courtship displays and the establishment of new territories. Twitter calls have only been heard in flight, either by a male escorting a female or during brief intraspecific territorial disputes.[11] Mixing of the two calls occurs occasionally, but little ecological research can explain its use.
Similar to other swallows, violet-green swallows are specialized aerial insectivores, catching and eating their prey while in flight. However, they have been known to feed higher in the sky than most other swallows. The examination of the stomach contents of multiple individuals has presented a wide range of diet items, including insects like ants, beetles and flies as well as other arthropods such as spiders.[2] On rare occurrences these birds have been observed foraging along the ground, but such events represent exceptions to their typical feeding habits.[12][13]
Violet-green swallows will usually arrive at their breeding area weeks prior to the start of reproduction. Location dependent, copulation takes place mid-May with the eggs being laid by the start of June, followed by a couple weeks of incubation before hatching. The average clutch size is 5 eggs, with females laying approximately 1 per day. During the weeks post-hatching, the parents feed their young as they slowly begin to grow their feathers. After approximately 3 weeks the young are ready to leave the nest. It is more common for pairs to reproduce once per breeding season, but a second brooding has been observed on occasion.[14]
Violet-green swallows are secondary cavity nesters, meaning they typically nest in natural holes or previously occupied nests.[15][16] Some breeding pairs will even go as far as usurping nests from other species.[17] A majority of violet-green swallow nests are in tree holes excavated by other animals or within the cracks of large cliffs.[9][14] Due to their dependence on large trees, violet-green swallows are highly impacted by forest management practices.[16] In addition to nesting in natural cavities, violet-green swallows have also been observed occupying artificial nest boxes.[18] Pairs typically breed in independent nests, except on cliffs where large colonies can be found nesting together.[2]
Violet-green swallows have been observed cooperating and competing with various avian species, including western bluebirds.[17][19] A similar field observation notes a violet-green swallow laying an egg in an active bluebird nest box. Initially, the male bluebird attempted to drive the swallow from the nest cavity, while the female bluebird did not seem concerned with the intruder. It appeared the bluebirds tolerated the act of egg-dumping by the violet-green swallow, but the observer returned the following day to find the newly laid egg smashed below the nest. This behaviour suggests that when unable to access her original nest after physiologically committing to laying her egg, a female violet-green swallow may participate in interspecific egg-dumping.[17]
Violet-green swallows are secondary cavity nesters and aerial insectivores, making males susceptible to nest and mate competition. To avoid being cuckolded, males spend more time guarding their mate than their nest, contrary to tree swallows. This paternity-defence behaviour emphasizes that non-territorial violet-green swallows exhibit greater mate competition than nesting site competition.[20]
Multiple accounts of violet-green swallows forming cooperative relationships with other species have been recorded. From 1981 to 1982, three independent swallow pairs were observed co-occupying the nest boxes of western bluebirds. These violet-green swallows protected the nesting site, removed fecal sacs from the boxes and fed the bluebird fledglings with no resistance from the adult western bluebirds. Despite too small of a sample size to hold statistical significance, fledgling survival was greater when violet-green swallows provided active care. It is believed that the swallows benefit from the cooperative relationship by inheriting the nest box after the bluebird parents and fledglings have left.[19]
Similar to the occasional observation of violet-green swallows building interspecific cooperative relationships, they have also been involved in interspecific competition for nesting sites. One example from 1974 noted the competitive behaviour between mountain chickadees and violet-green swallows. The physical altercation began when a pair of swallows attempted to overtake a nesting site occupied by a pair of chickadees and their fledglings. After multiple aerial battles, the chickadees regained control of their nest and successfully defended against future violet-green swallow attacks. The same field observer noted a similar altercation between violet-green swallows and hairy woodpeckers, which resulted in the same outcome. These species are permanent residents, allowing them first choice of nesting sites, while the violet-green swallows are summer residents with late breeding habits.[21] Thus, a scarcity of viable nesting sites may lead to this interspecific competitive behaviour in violet-green swallows. A similar observation of competitive behaviour for potential nesting sites has been observed between acorn woodpeckers and violet-green swallows.[11]
It has been speculated that certain birds, including swallows, enter a state of torpidity during harsh winter conditions. Few observations of this decrease in body temperature and metabolic rate have been recorded in violet-green swallows, the first case occurring in 1965 near Death Valley National Monument in Saratoga Springs, California. Field observers noted 3 “dead” individuals on the east-facing slope of a dune the morning after a cold and windy night. Upon closer observation, the violet-green swallows made minor movements, such as opening their eyes, but did not struggle while being handled. The physical appearance of the swallows, including the position of their head in relation to the slope and the fluffing of their feathers was similar to that of other birds in torpor. Despite the lack of thermometers, it was apparent these 3 individuals were in a state of hypothermia for about 45 minutes after the sun began to rise. Eventually the 3 swallows awkwardly flew off, signifying the end of their torpor bout.[22]
In addition to reaching borderline hypothermic temperatures during bouts of torpor,[22] violet-green swallows have been observed behaving similar to hyperthermic individuals while sunbathing. Indications of this activity include the orientation of their wings and tail, their trance-like state and the occasional loss of balance. Research has shown that increasing feather temperatures during basking can control ectoparasites. The period of sunbathing in violet-green swallows is short and dependent on ambient temperature and wind velocity, but typically occurs after an increase in parasite loads near the end of nesting.[23]
The violet-green swallow (Tachycineta thalassina) is a small North American passerine bird in the swallow family. These aerial insectivores are distributed along the west coast from Alaska to Mexico, extending as far east as Montana and Texas. With an appearance very similar to the tree swallow, these individuals can be identified by the white rump side-patches that appear to separate their green back and purple tail. Violet-green swallows are secondary cavity nesters, found in a number of habitats including deciduous and coniferous forest. In addition to nesting in tree holes within these habitats, they are also widely observed nesting in the cracks of large cliffs.
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