There are three recognized subspecies: Q. q. versicolor, often called the bronzed grackle; Q. q. quiscula, known as the Florida grackle; and Q. q. stonei, often referred to as the purple grackle. In areas where the bronzed and purple grackles overlap, a small amount of intermediate forms have been designated Q. q. ridgwayi, and show strong barring on the backs.
Albinism has been recorded fairly often in this species, but it is usually partial.
Common grackles use physical displays and vocalizations to communicate. Common grackles produce one song type, which is individually distinctive and is probably used as identification. The harsh song is said to sound much like a squeaking, rusty gate. The male song is most often heard around the date of the first copulation, and its frequency decreases over the course of incubation. Females sing much less frequently than males, and appear to sing most often when song-answering with their mate.
Communication Channels: visual ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
Common grackles are one of the most successful and wide-spread species in North America, with an estimated total population of 97,000,000 individuals. Eastern forests were cleared for agriculture in 1700s and 1800s, creating additional nesting habitat and increased food sources. The planting of shelterbelts has facilitated the spread of this species in the west. Common grackles are very common, and are killed as an agricultural pest in many parts of their range.
US Migratory Bird Act: protected
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Common grackles are one of the most significant agricultural pests today, causing millions of dollars in damage to sprouting corn. The roosting sites of common grackles and other blackbirds may harbor the fungus, which causes histoplasmosis, a human respiratory disease that can be fatal. However, only roost sites that have been used for more than 3 years tend to become infected. Nonetheless, this phenomenon is used as one of the primary justifications for killing large numbers of roosting blackbirds and starlings.
Negative Impacts: injures humans (carries human disease); crop pest
Common grackles may help to control populations of crop pests.
Positive Impacts: controls pest population
Common grackles provide food for several birds and small animals as well as helping to control populations of insects and other prey. They also disperse seeds through their droppings during the parts of the year when seeds make up most of their diet.
Common grackle nests are occasionally parasitized by brown-headed cowbirds, although cowbird eggs in these nests are largely unsuccessful.
Ecosystem Impact: disperses seeds
During breeding, common grackles' diets consist mainly of insects and other invertebrates. The diet may also include goldfish, minnows, crayfish, small frogs, salamanders, mice, and small bats, which are caught from the air. During migration and winter, common grackles eat mostly grains from farm fields and seeds, particularly corn and acorns. They also eat some fruits.
Common grackles are generally very opportunistic foragers, they follow plows in search of grubs, and even consume human garbage. Adults have been observed snatching earthworms from feeding robins. Grackles forage primarily on the ground, though they also utilize trees, shrubs, and other vegetation. These gregarious birds feed in large flocks, especially outside of the breeding season. They primarily use their bills instead of their feet to uncover food on the ground.
Animal Foods: birds; mammals; amphibians; fish; insects; terrestrial non-insect arthropods; terrestrial worms; aquatic crustaceans
Plant Foods: seeds, grains, and nuts; fruit
Primary Diet: carnivore (Insectivore , Eats non-insect arthropods)
Common grackles range over almost all of eastern North America east of the Rockies, extending far into Canada in the summer breeding season.
Biogeographic Regions: nearctic (Native )
Common grackles are found in open areas with scattered trees (preferably coniferous), including around human habitation. They can also be found in farmlands, orchards and swamps. Common grackles have adapted so well to human structures that they are quite common in open areas such as suburban developments, city parks and cemeteries. In fact, human alteration of forested habitats for agriculture has resulted in an expansion of the range of common grackles and an increase in their numbers.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: savanna or grassland ; forest
Other Habitat Features: urban ; suburban ; agricultural
The maximum lifespan recorded is just over 22 years, although most do not live that long. About half of all common grackles reach adulthood.
Range lifespan
Status: wild: 22 (high) years.
Average lifespan
Status: wild: 275 months.
Common grackles are medium-sized blackbirds. Their plumage is black, and has a sheen that is glossy and iridescent. Generally, their heads, necks and breasts are glossy purplish-blue or bluish-green. However, common grackles in different parts of North America have somewhat different colored plumage. In New England and in the West, the subspecies has a brassy bronze body coloration. East of the Allegheny Mountains, the body is purple, and in the southeast the feathers have a greenish hue. Common grackles have long, sharp, black bills and yellow eyes. Their tails are long and keel-shaped.
Adult common grackles are 28 to 34 cm long. Females are smaller and duller than males and have a shorter tail. Males usually weigh about 122 g while females weigh around 94 g. Young common grackles look similar to adults, but have brown plumage and brown eyes.
Range mass: 92 to 131 g.
Range length: 28 to 34 mm.
Other Physical Features: endothermic ; bilateral symmetry ; polymorphic
Sexual Dimorphism: male larger; sexes colored or patterned differently; male more colorful
Humans kill large numbers of common grackles to control populations in areas where they destroy crops. Fox squirrels, eastern chipmunks, rat snakes, domestic cats, gray squirrels, bullsnakes, and racoons eat the eggs and nestlings of common grackles. Red-tailed hawks, northern harriers, Cooper's hawks, short-eared owls, and great horned owls are predators of adult common grackles.
Known Predators:
Common grackles are usually monogamous, though polygyny occasionally occurs. Pair formation begins in flocks in early spring. Formation of pairs is indicated by flights and mutual displays between a single female and multiple males. A male and a female show preference for one another by flying together, usually with the female in the lead. As the pair-bond is established, the pair leaves the flock to fly and sing together.
The female of a pair typically chooses the nest site. Though this is usually done after pair formation, females sometimes chosen sites several weeks before pairing with a male. From pair formation through incubation, the male remains in close association with his mate by perching near her, following her, and engaging in mutual displays. This pattern exhibited by the male probably functions to guard against extra-pair copulations. Once incubation has begun, his attentiveness decreases steadily.
Adult common grackles sometimes function as helpers to other birds of the species. In one recorded case, two males frequently showed up at the same nest to feed the young, and there was no antagonistic behavior between them. It is assumed that one of the males was the father of the offspring.
Mating System: monogamous ; cooperative breeder
Common grackle nests are built by the female, usually in coniferous trees, though more unusual sites have been documented. These include woodpecker holes, on rafters, under the eaves of barns, in the crannies of ospreys' large nests, and in clumps of cattails. The nests are large and bulky, constructed of woody stems, leaves and fine grasses. Other materials may be used, including fishing line, feathers, manure and tape. The nest cup is lined with mud, and finally fine grasses and horsehair.
Copulation begins soon after the female has completed the nest. She lays 1 to 7 eggs (usually 5 to 6). The eggs are smooth-textured, and highly variable in color. They are typically light blue to pearl gray, though they range from nearly white to dark brown. Some are scrawled with blackish brown, especially at the larger end, and others are spotless. The female incubates the eggs for 12 to 14 days. At this time, about half of common grackle males desert the female and the nest. Those that remain participate in parental care after hatching.
During incubation, various displays and calls are given by both sexes. Parental care, including brooding and feeding, is performed mainly by the female, although males have been observed feeding young. The food supply is monopolized by more aggressive nestlings. The young leave the nest about 12 to 15 days after hatching, and remain near the nest for another 1 to 2 days. The adults continue to feed the young for several weeks.
Common grackle nests are sometimes parasitized by brown-headed cowbirds, but the cowbird eggs in these nests are largely unsuccessful. Common grackles are usually single-brooded, but can double-brood in some areas. Common grackles breed between March and July.
Breeding interval: Common grackles breed once yearly. Common grackles are usually single-brooded, but can double-brood in some areas.
Breeding season: Common grackles breed between March and July.
Range eggs per season: 1 to 7.
Average eggs per season: 5.
Range time to hatching: 12 to 14 days.
Range fledging age: 12 to 15 days.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Average birth mass: 105 g.
Average eggs per season: 5.
Brooding and feeding of the altricial chicks are performed mainly by females, although there have been reports of males assisting in feeding the young. The food supply is monopolized by more aggressive nestlings. The young leave the nest about 12 to 17 days after hatching, though they remain near the nest for another 1 to 2 days. Adults continue to feed the young for several weeks. About half of all grackle males remain with the female through hatching and help in the parental care of the young.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Female); pre-independence (Provisioning: Male, Female)
