Quiscalus quiscula
common grackle

Common grackles range over almost all of eastern North America east of the Rockies, extending far into Canada in the summer breeding season. (Terres, 1980)

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. (Peer and Bollinger, 1997; Terres, 1980)

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. (Peer and Bollinger, 1997; Terres, 1980)

The maximum lifespan recorded is just over 22 years, although most do not live that long. About half of all common grackles reach adulthood. (Terres, 1980)

Common grackles are very gregarious. Even during the breeding season, grackles that are not incubating roost together at night. The roosts can be as large as thousands of individuals, including other species of birds, such as red-winged blackbirds, European starlings, and brown-headed cowbirds. Breeding pairs nest singly or in colonies, sometimes with up to 200 pairs in one colony.

Though they are highly gregarious, grackles do attack other grackles as well as other species of birds. Attacks on other birds may involve biting, pecking, scratching, and flying toward the adversary. Common grackles eat other birds' eggs and nestlings, and occasionally kill and eat other adult birds, particularly adult house sparrows. Grackles are territorial only around the nest site. Pairs actively defend their nest by mobbing, chasing or diving at predators, including humans. Common grackles migrate in mixed-species flocks with the above-mentioned species. Most common grackle populations make seasonal movements between breeding and wintering sites. However, populations that breed in the Gulf Coast states are largely nonmigratory. For those birds that do migrate, the wintering range is usually not far south of the breeding range. A magnetic material (magnetite) has been found in the head and neck of common grackles, suggesting that they may use geomagnetic fields to navigate. (Peer and Bollinger, 1997; Terres, 1980)

Home Range

We have no information regarding the home range of common grackles. (Terres, 1980)

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.

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. (Peer and Bollinger, 1997; Terres, 1980)

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. (Peer and Bollinger, 1997)

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.

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. (Peer and Bollinger, 1997)

Common grackles may help to control populations of crop pests.

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. (Peer and Bollinger, 1997)

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.

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 agnostic behavior between them. It is assumed that one of the males was the father of the offspring. (Peer and Bollinger, 1997; Skutch, 1996; Terres, 1980)