Cowbird

You know how it is. Once someone gets a bad reputation, they’re deemed responsible for all kinds of mischief, deservedly or not. So it is with cowbirds, who leave the care of their young (from eggs to adulthood) to other species. The unlucky foster parents are often warblers, sparrows or finches.

Brown-headed Cowbird photographed by Will Elder of the National Park Service

The female cowbird locates a potential host during nest construction and waits until the host lays her eggs.  The day before laying her single egg, the cowbird removes one host egg from the nest and then replaces it with her own.  She will repeat the behavior up to five times each season.

Research shows that less than five percent of cowbird eggs develop to adulthood.  Nevertheless, the population is increasing due to the sheer number of eggs laid.  The large cowbird offspring often crowd and starve out the host’s young.

The Brown-headed Cowbird is the smallest North American blackbird and a relative newcomer to the northwest.  The male is metallic green-black with a coffee brown head.  The female is lighter brown.

Cowbirds get their name from flocking around herds of moving cattle eating insects aroused by the activity.  Once confined to the open grasslands of middle North America, cowbirds have surged in numbers and range as humans built towns and cleared woods.  You may see a cowbird at your feeder, dining on seed and berries.