Tuesday, November 25, 2014 · 4:57 p.m.

Riverwalk Bird of the Week: Brown-headed cowbird

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Once confined to the open grasslands of middle North America, cowbirds have surged in numbers and range as humans built towns and cleared woods. (Photo: Bret Douglas)

The folks in the Riverwalk Bird Club don't just watch birds. The group includes some excellent photographers.

Nooga.com Outdoors is happy to share their great photos by featuring a Bird of the Week.

This week, we feature a brown-headed cowbird, taken by Bret Douglas.

The brown-headed cowbird is a stocky blackbird with a fascinating approach to raising its young. Females forgo building nests and instead put all their energy into producing eggs, sometimes more than three dozen a summer. They lay these in the nests of other birds, abandoning their young to foster parents, usually at the expense of at least some of the host’s own chicks.

Interesting facts
—The brown-headed cowbird is North America’s most common “brood parasite.” A female cowbird makes no nest of her own but instead lays her eggs in the nests of other bird species, who then raise the young cowbirds.

—Brown-headed cowbirds lay eggs in the nests of more than 220 species of birds. Recent genetic analyses have shown that most individual females specialize on one particular host species.

—Social relationships are difficult to figure out in birds that do not build nests, but male and female brown-headed cowbirds are not monogamous. Genetic analyses show that males and females have several different mates within a single season.

—Some birds, such as the yellow warbler, can recognize cowbird eggs but are too small to get the eggs out of their nests. Instead, they build a new nest over the top of the old one and hope cowbirds don’t come back. Some larger species puncture or grab cowbird eggs and throw them out of the nest. But the majority of hosts don’t recognize cowbird eggs at all.

—Cowbird eggs hatch faster than other species' eggs, giving cowbird nestlings a head start in getting food from the parents. Young cowbirds also develop at a faster pace than their nest mates, and they sometimes toss out eggs and young nestlings or smother them in the bottom of the nest.

—In winter, brown-headed cowbirds may join huge roosts with several blackbird species. One such mixed roost in Kentucky contained more than 5 million birds.

—The oldest recorded brown-headed cowbird was 16 years, 10 months old.

This information is courtesy of the Cornell Lab of Ornithology. 

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