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Scientific Name: Quiscalus quiscula
Common Name: Common Grackle

(Information for this species page was gathered in part by Mr. Scott Williams for Biology 220W in Spring 2009 at Penn State New Kensington)

Common grackle eating seedsThe common grackle (Quiscalus quiscula) is a large (twelve and a half inches long) blackbird with bright, yellow eyes, and a stout, black bill. Its head, neck, and breast feathers are glossy and iridescent with a green to blue-purple sheen. Female grackles are slightly smaller than males and are also slightly less iridescent. Immature grackles have dull, brown feathers and dark, brown eyes.
(Image: D. Sillman)

Common grackles are found all across the United States and southern Canada. They are one of the most abundant birds in North America, although census data has indicated that their population has declined in recent years. Their northern-most ranges are abandoned during the winter, but grackles do not extensively migrate. In their southern ranges individuals may remain in or near their breeding territories all year round.

Common grackles will eat almost any food that they can find. Insects and other invertebrates are preferred the year-round, but they will also consume small mammals (especially mice), fish, frogs, fruit, corn (right from the field both during planting and also from spillage after harvest), acorns, and seeds. They frequent backyard birdfeeders and through their aggressive behaviors drive other bird species away from the seed resource. I have also observed grackles eating Japanese beetles and gypsy moth caterpillars. During our last major gypsy moth outbreak in the 1990’s the grackles would pick the caterpillars off the trees in my side yard and take them to the nearby road to wipe them across the rough asphalt to remove the irritating spines before they ate them. They also feed on human refuse and are relentless foragers. Their interactions with humans in rural, suburban, and urban environments have increased their numbers and continental distribution over those that were seen in pre-European-settlement North America.

Mating and Reproduction
In early spring, common grackles begin the process of mating pair formation. Small groups made up of a single female and several males begin to make short flights around their territory. The males in these flights hold their tails in a “V-shaped” configuration (reportedly the only time that this tail conformation is observed). Over a period of one to six weeks the number of males in these flight groups declines until there is only one male left paired with the female. This couple will then copulate and fly off in search of a nest site.

Typically the female will select the nest site and then begin to build the nest without any assistance from the male. Grackles may nest in groups as large as two hundred pairs. Interestingly, a number of blackbird species may nest in the grackle’s colony. Nests are frequently, but not exclusively, located in conifers. The nest is a bulky, cup-shaped mass made up of sticks, plant stems, leaves, and grasses. It may be lined with mud, fine grass, or animal hair. Many nests are built, but almost half are abandoned during construction before any eggs are laid.

Females lay one to seven, light blue to gray, spotted eggs (four or five are the average). Eggs vary in size and color depending on the order that they are produced. Later eggs tend to be lighter in color and larger than earlier eggs. The two week incubation is carried out exclusively by the female. The male may remain with the female during this period, but approximately half of the males do not. Departed males may mate with other females but may also return to assist the female in feeding the nestlings and fledglings.

Nestlings fledge in twelve to fifteen days. Fledglings may be fed by parents for several more weeks. Male nestlings eat more than female nestlings since they have to grow to a larger size before fledging. During period of food shortages the parental birds will preferentially feed the female nestlings (often leading to male nestling starvation) in order to take advantage of their more efficient growth energetics.

Interesting Behaviors
Common grackles (like many other bird species) display a behavior called “anting.” Anting involves a bird lying down directly on or very close to an active ant nest. The ants, then, swarm over the bird and crawl and burrow in and among its feathers. This behavior is thought to stimulate the ants to secrete formic acid throughout the bird’s plumage. Formic acid is in turn thought to decrease the often heavy parasite load being carried by the bird. Grackles have also been observed to introduce choke cherries, marigold blossoms, lemons, limes, and walnut juice into their feathers possibly in attempts to rid themselves of parasites.

Groups of grackles foraging in a common feeding area frequently display dominance and aggression behaviors toward each other. One of these behaviors is the “bill-tilt.” Interacting birds tilt their heads upward and point their bills toward the sky. The more dominant the bird, the more upwardly tilted their heads!

In the winter, grackles form large flocks with other blackbird species (including red-wing blackbirds, cowbirds, and European starlings). These flocks can number over a million individual birds and are frequently observed rising, cloud-like from harvested agricultural fields or swarming the canopy of a forested site in which an abundance of late season fruit or seeds has been detected.

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