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.  These they lay 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.  Many people consider them a nuisance bird, since they destroy the eggs and young of smaller songbirds.  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 the nestlings a head start in getting food from the parents.  Young cowbirds also develop at a faster pace than their nest mates and they may toss out eggs and young nestlings or smother them in the bottom of the nest.

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In winter Brown-headed Cowbirds may join huge roosts with several blackbird species.  The oldest recorded Brown-headed Cowbird was a male, and at least 16 years 11 months old.  Brown-headed Cowbirds feed mostly on seeds from grasses and weeds, with some crop grains.  They also eat insects such as grasshoppers and beetles.  Female cowbirds have a large calcium requirement from laying so many eggs.  To satisfy it, they eat snail shells and sometimes eggs from nests they have visited.  The eggs have been found in nests of over 140 different bird species.

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They will lay 1-7 eggs at one time with an incubation period of 10-12 days.  They stay in the nest for 8-13 days and are naked at hatching except for sparse tufts of down, eyes closed and clumsy.  Brown-headed Cowbirds are common across most of North America and with an estimated breeding population of 130 million, they are a species of low conservation concern.  They threaten other species with their nest parasitism.