Brown-headed Cowbirds are small blackbirds with short cone-shaped bills and long, pointed wings. Males appear black with a unique brown head and neck. Females are either dullish gray or brown. Their bills are a dull grey, while their eyes are black. Adult males weigh between 40 and 50 g, and females are about 10% smaller.
Brown-headed Cowbirds breed from southeastern Alaska, through Canada and the entire continental United States to central Mexico. They winter throughout the southern portions of this range, and also in southern Mexico and the tip of Florida.
Brown-headed Cowbirds prefer habitats with low or scattered trees among grassland vegetation, such as woodland edges, brushy thickets, prairies, fields, pastures, orchards, and residential areas.
Brown-headed Cowbirds lay their eggs in the nests of other birds; female Cowbirds select host nests of another species of bird to lay their eggs in. They wander about, laying eggs in as many nests as they can find and laying up to 40 eggs per season. They lay sequences of 7 eggs, one egg laid in a different nest each day, then rest for several days between egg-laying sequences. The young are then cared for by the host bird. There are 144 different host species documented that raise Brown-headed Cowbird young, so the incubation and parental care of Brown-headed Cowbirds varies greatly depending on the nest in which they are deposited. During the various care processes for Brown-headed Cowbirds, however, they are always fed more often than the young of the host species because they are very active in begging for food from the parents and tend to be bigger than the host species' nestlings. The smallest recorded host of cowbird young is the Brown Creeper, while the largest host is the Meadowlark. Eggs hatch about 9 to 12 days after being laid in the host nest. This is a fairly common length of time for the eggs of the host birds as well. If they survive, they leave the nest in about 8-13 days but continue to be fed by the host parents for between 18 and 35 days. Female Cowbirds are ready to breed when they are 1 year old, but males often take longer. Cowbirds breed between April and June with variation depending on area.
These birds are brood parasites, they lay their eggs in the nests of other birds. These hosts provide all the parental care.
The oldest known wild Brown-headed Cowbird was 15 years and 10 months old, most do not live nearly as long.
Brown-headed Cowbirds rarely hop when on the ground, preferring to walk. They are often found in mixed-species flocks with other blackbirds, such as Common Grackles. Brown-headed Cowbirds get their name from their close association with livestock, such as horses and cattle, which disturb insects on the ground when feeding. This allows cowbirds easy access to their food. Because cowbirds have a significant impact on the reproductive success of other species, many other bird species have adapted and can recognize this threat, acting aggressively towards Brown-headed Cowbirds near their nesting territory. Brown-headed Cowbirds are active during the day and migrate short distances between northern breeding areas and more southerly wintering areas.
Brown-Headed Cowbirds have a wide variety of calls, such as glug glug glee, bublowcomseee, bub ko lum tseee, glug glug, whssss, pseeee, ch'ch'ch'ch'ch,' kek, kik, and tek. They tend to sing in the winter shortly before mating season. They sing most often at sun-rise and almost never sing while in flight. Each individual Cowbird is thought to have an extensive repertoire. Brown-headed Cowbirds also use their eyesight to distinguish appropriate host species and for communicating among themselves.
Brown-headed cowbirds often feed on the ground, away from vegetation. Their main food items are seeds and insects. They sometimes hunt in the air, looking for slow flying insects. Their diet is nearly 75% 'weed' seed, with most of the remaining 25% made up of grasshoppers and beetles.
Cowbird eggs can be lost when host species reject them. Not all hosts reject cowbird eggs, but when they do, they may push them out of the nest (for example, robins and catbirds), bury them under a new nest lining (for example, yellow warbler), or desert the nest.
Predators on fledgling cowbirds include blue racers, black rat snake, and blue jays. Raptors and owls may also prey on cowbirds as adults. A wide range of nest predators probably takes brown-headed cowbird nestlings, along with those of their hosts, including blue jays, raccoons, skunks, opossums, American crows, northern shrikes, and snakes.
Cowbirds have been known to mob great horned owls.
Not only do cowbirds, provide food for many animals, they also help to control insect populations and disperse seeds.
Fragmentation of forest habitat in North America has resulted in a great increase in the edge habitats favored by Brown-headed Cowbirds, and a reduction (and in many places an elimination) of forest-interior habitats that they do not penetrate. As a result, a number of other forest birds' nests are now being used by Brown-headed Cowbirds at a much increased rate. This parasitism may be one cause in the general decrease in numbers of songbirds in North America.
The cowbird eats many insects which are pests to humans.
Brown-headed Cowbirds are common. They do, however, pose a threat to the populations of other birds, such as the Kirtland's Warbler, Black-Capped Vireo, and Least Bell's Vireo, whose small populations are frequently parasitized by Brown-headed Cowbirds. This has led to programs that involve trapping and killing of Brown-headed Cowbirds at specific breeding areas where other species are threatened.
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.
uses sound to communicate
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.
an animal that mainly eats meat
uses smells or other chemicals to communicate
animals that generate their own body heat through metabolic processes.
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
An animal that eats mainly plants or parts of plants.
fertilization takes place within the female's body
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).
makes seasonal movements between breeding and wintering grounds
Having one mate at a time.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats all kinds of things, including plants and animals
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).
having more than one female as a mate at one time
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
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).
Living on the ground.
uses sight to communicate