Cowbird. What a crazy name for a creature with feathers and wings.  Their scientific name is Molothrus ater.  The first is a Greek word that means vagabond, tramp, or parasite and very well describes the bird’s lifestyle.


A male brown-headed cowbird

These birds found a way to make a living by following the great hoofed herds of the western hemisphere.  It is believed they originated in South America and made their way north where they encountered the ultimate feast provided by millions of bison roaming across the plains. When ungulates graze, they leave behind rich fertilizer that attracts insects, which attracts birds.  Brown-headed cowbirds found that living near these herds was very beneficial, except when it came to raising young.

Building a nest, laying and incubating eggs and then feeding chicks can take anywhere from two to three months.  Bison herds did not stay in any one place that long, so the cowbirds (which we should actually call bisonbird) had to make an adjustment in their reproductive strategy.  They decided to go with absentee parenting.


A mixed group of blackbirds; redwing in the foreground, cowbirds behind.

After locating the nest of another songbird the female cowbird makes a stealth landing when the other female is away, drops an egg in the nest and leaves. As many as 220 species have been identified as hosts and over 140 of these have been known to raise the alien young. Most other birds do not seem to recognize that the much larger egg is not theirs, but there are exceptions.  Yellow warblers have over the generations learned that the only way to avoid becoming unwilling parents to this alien egg is to build a new nest on top of the first one, even if they already laid their own eggs.  Some species that realize they’ve been parasitized will break or remove the cowbird’s egg.  For those who don’t, there will be an extra (large) mouth to feed – one that often hatches earlier than their own young and becomes a demanding, fast growing stranger.

Since the female can produce as many as three dozen eggs in one summer, she must replenish her calcium requirements by eating snail shells and sometimes eggs taken from nests she visits. Grasshoppers and beetles make up about a quarter of their diet. Originally seeds of grasses and weeds were their main food, but with the loss of the great herds, the clearing of forests, and growth of towns, cowbirds have altered their lifestyle again, to live closer to humans.  We have cowbirds come to our birdfeeder occasionally and they will readily eat millet, milo, oats, peanut hearts, cracked corn, as well as black shelled and hulled sunflower seeds.  You might not find them as beautiful as the other blackbirds, but the males are handsome with their glossy black back feathers and chocolate brown head.  A thick, finch like beak lets them eat the variety of hard shelled seeds.

Going back to the original question about names, some of the other common ones for the cowbird include; brown-headed oriole, cow bunting, cuckold, and lazybird.

By Kate Crowley

Photos by Mike Link