Common grackles are large birds widely distributed across much of North America. Adults have a long, dark bill, pale yellowish eyes, and a long tail; their feathers appear black with purple, green, or blue iridescence on the head, and primarily bronze sheen in the body plumage. Adult females, beyond being smaller, are usually less iridescent; their tails, in particular, are shorter, and unlike the males, do not keel (display a longitudinal ridge) in flight and are brown with no purple or blue gloss. Juveniles are brown in color with dark brown eyes.
Common grackles breed across North America east of the Rocky Mountains. These birds are permanent residents in much of their range; northern birds migrate in flocks to the Southeastern United States. Common grackles prefer open woodlands near swamps and marshes and are well adapted to human habitats such as farmlands, parks, large gardens, and urban residential areas.
Common grackles are noisy and gregarious birds; they migrate, nest and roost in large flocks often with other birds. They are active during the day spending most of the time foraging on the ground, in shallow water, or in shrubs; they may also steal food from other birds. Grackles at outdoor eating areas often wait eagerly until an unwary bird drops some food. They rush forward and try to grab it, often snatching food out of the beak of another bird. Grackles prefer to eat from the ground at bird feeders, and often forage for insects after a lawn trimming. Despite their social nature, Common grackles are territorial around their nests. In the breeding season, males tip their heads back and fluff up feathers to display and keep other males away. This same behavior is used as a defensive posture to attempt to intimidate predators. Common grackles communicate vocally and their song is particularly harsh, especially when these birds, in a flock, are calling. Songs vary from year-round "chewink chewink" to a more complex breeding season "ooo whew,whew,whew,whew,whew" call that gets faster and faster and ends with a loud "crewhewwhew"! It also occasionally sounds like a power line buzzing.
Common grackles are serially monogamous and form pairs bonds that last only within one breeding season. Polygynous mating system, in which one male may mate with more than one female, occasionally occurs. They usually breed between March and July. These birds often nest in colonies, some being quite large. The nest is a well-concealed cup in dense trees (particularly pine) or shrubs, usually near water; sometimes, pairs nest in cavities or in man-made structures or even in bird houses. The female lays 4 to 7 eggs which she incubates alone within 12-14 days. The chicks are altricial; they are hatched naked with come brownish down and closed eyes. The young fledge and leave their nest about 12 to 15 days after hatching but usually remain with their parents for one or two days more.
Common grackles are considered a pest by farmers because of their large numbers and fondness for grain and seeds; they cause serious damage to corn, sunflower, and other crops. Forced lethal control measures that are often used to stop the damage may influence the Common grackle population declines.
According to the IUCN Red List, the total population size of Common grackles is 69 million mature individuals, equating to 103.5 million individuals. Currently, this species is classified as Near Threatened (NT) on the IUCN Red List and its numbers today are decreasing.
Due to their fondness of grains and seeds, Common grackles act as seed dispersers in their ecosystem. These birds also control populations of insects and other prey items they consume in the diet and in turn they provide food for local predators.