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Brown-headed cowbirds are notorious for the unusual approach to raising their young, or the lack thereof. Known as brood parasites, cowbirds lay their eggs in the nests of other birds. These unsuspecting “foster parents” are called hosts, and will usually raise young cowbirds at the expense of their own. Talk about an aviary freeloader.
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Male brown-headed cowbirds sport glossy black plumage with a green sheen and a dark-brown head. Females are much less showy, with dull grayish brown feathers. The bland appearance of the female allows them to observe possible hosts building nests without drawing suspicion. Once the location of a good nest is known, the cowbird will return during the host specie's egg-laying period in hopes it will go unnoticed. Because cowbird eggs typically hatch earlier than those of the host, the cowbird has an advantage, in more ways than one.
In most parasitized nests, the brown-headed cowbird removes one of the host eggs before laying its own to ensure it is incubated. Once hatched, the fledgling continues to severely affect the host family. As cowbirds are usually quite larger than the host specie, the fledgling can dominate other nest-mates in space occupied and during feeding. They develop faster too, sometimes nudging out eggs and smaller fledglings to give themselves more room. While the impact varies for different host species, what usually occurs is the loss of at least one of the host's young.
More than two hundred species are known to be parasitized by brown-headed cowbirds. While some species evict cowbird eggs and fledglings from their nests, many species end up hatching the somewhat lazy bird’s young.
More Facts about the Brown-headed Cowbird
- Cowbirds are known as such because they once followed grazing animals such as bison to feed on what was kicked up in their wake. They remain somewhat associated with large mammals such as cows.
- Groups of cowbirds are known as a "herd" or "corral."
- In the winter, brown-headed cowbirds join several other species of blackbirds to form large roosts, numbering well in the thousands.
- Their song is characterized by a somewhat gurgling "glug-glug-glee" tune. They are very noisy birds.
- Cowbirds prefer grasslands with scattered trees, prairies and residential areas. While many species of birds are negatively affected by development and fragmentation of their habitat, the cowbird has been able to increase in numbers as they avoid thick forests.
- As ground foragers, you'll find brown-headed cowbirds feeding on seeds with other blackbirds and starlings.