Quiscalus quisculacommon grackle

Geographic Range

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)

Habitat

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)

Physical Description

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)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • male more colorful
  • Range mass
    92 to 131 g
    3.24 to 4.62 oz
  • Range length
    28 to 34 cm
    11.02 to 13.39 in

Reproduction

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

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. (Peer and Bollinger, 1997; Skutch, 1996; Terres, 1980)

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. (Peer and Bollinger, 1997; Skutch, 1996; Terres, 1980)

  • 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
  • Average eggs per season
    5
    AnAge
  • Range time to hatching
    12 to 14 days
  • Range fledging age
    12 to 15 days

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. (Peer and Bollinger, 1997; Skutch, 1996; Terres, 1980)

  • 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

Lifespan/Longevity

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)

Behavior

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)

Communication and Perception

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.

Food Habits

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)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • fish
  • insects
  • terrestrial non-insect arthropods
  • terrestrial worms
  • aquatic crustaceans
  • Plant Foods
  • seeds, grains, and nuts
  • fruit

Predation

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)

Ecosystem Roles

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

Economic Importance for Humans: Positive

Common grackles may help to control populations of crop pests.

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

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)

  • Negative Impacts
  • injures humans
    • carries human disease
  • crop pest

Conservation Status

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)

Other Comments

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. (Peer and Bollinger, 1997; Skutch, 1996; Terres, 1980)

Contributors

Tanya Dewey (author), Animal Diversity Web.

Kari Kirschbaum (editor), Animal Diversity Web.

Alicia Ivory (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cooperative breeder

helpers provide assistance in raising young that are not their own

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5? N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

Peer, B., E. Bollinger. 1997. Common Grackle (Quiscalus quiscula). Pp. 1-20 in A Poole, F Gill, eds. The Birds of North America, Vol. 271. Philadelphia, PA: The Academy of Natural Sciences and Washington, DC: The American Ornithologist's Union.

Skutch, A. 1996. Orioles, blackbirds and their kin: A natural history. Tuscon: University of Arizona Press.

Terres, J. 1980. The Audobon Society Encyclopedia of North American Birds. New York: Alfred A. Knopf.