Pest spotlight: Common grackles

Common grackles are ground feeders of grain and insects. (Photo: Christopher R Mazza / iStock / Getty Images Plus / Getty Images)

Numbering in the tens of millions, grackle populations in North America can be a nuisance in urban and suburban areas as well as agricultural areas. These noisy, messy birds can attack people and pets when they perceive a threat to their nests or young.

In some winter roosts, grackles concentrate on powerlines, as well as on nearby trees and shrubs. When grackles depart from powerlines as a large group, which is called a plague, the lines can move wildly and contact other lines or structures, causing power outages. Their droppings also can facilitate growth of the fungus Histoplasma capsulatum — resulting in an increased risk for humans for the lung infection histoplasmosis.

The U.S. Fish and Wildlife Service’s Migratory Bird Treaty Act of 1918 federally protects grackles, but control strategies are allowed under a “Standing Depredation Order” (50 CFR 21.43). At press time, the federal standing depredation order continues to override state regulations or the need for a state permit.

Biology and behavior

Because of their gregarious nature, grackles are easily observed and identified. The common grackle is part of the family Icteridae, which includes blackbirds, orioles, cowbirds, meadowlarks and bobolinks.

The common grackle is 12.5 inches long, with a wing span of 17 inches. It weighs about 4 ounces, boasting glossy black feathers and pale yellow eyes.

The male’s feathers are iridescent purple on the head, nape and breast, with bronze iridescence on the body and wings. Females are slightly less glossy than males. Young birds are dark brown with dark eyes.

The common grackle’s song consists of a harsh, toneless hiss (“kh-sheee” or “kh-reezzh”). Its call is a harsh, dry “karrz” or “kerrr,” and the male’s call is a thin, wheezy, toneless “zweeesh” and a nasal, hoarse “krrrjk.”

Breeding habits

The common grackle breeds throughout the United States and southern Canada east of the Rocky Mountains and south of Hudson Bay. It winters from Nebraska to Texas and east to Pennsylvania and Florida. A native to North America, its range may have expanded because of agriculture and climate.

Grackles breed during their first year. Their average clutch size is one to seven eggs; they can have up to two clutches per year.

Female grackles build nests, preferably in the tree canopy and out of reach of predators. Grackle males assist in defending the nest and raising chicks.

Following a nest-building period of one to six weeks, female grackles lay their eggs. Incubation for all grackle species is 11 to 15 days. The chicks fledge in 10 to 17 days. Molting occurs during late summer.

Migrant blackbirds leave southern roosts in mid-February to early March.

Grackles primarily feed on grain, but also forage on the ground for worms, spiders, mice and the eggs of other birds. A combination of dispersal techniques, exclusion and lethal removal may help reduce grackle damage.

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from Pest Management Professional https://www.mypmp.net/2024/10/15/pest-spotlight-common-grackles/
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