"The two most characteristic habits of this bird are indicated in its names. The Greek word Molothrus signifies a vagabond, tramp, or parasite, all of which terms might well be applied to this shiftless vagabond and imposter. It deserves the common name cowbird and its former name, buffalo-bird, for its well-known attachment to these domestic and wild cattle." (Bent 1958).


The very common Brown-headed cowbird has a fascinating life history that is unfortunately detrimental to many other small birds. The males are quite handsome with iridescent blackish bodies and a brown head. The females are relatively nondescript brownish birds. The Brown-headed cowbird is a relative newcomer to the east. It is believed to have reached the east coast sometime following European settlement of the new world from its Pre-colonization range in the grasslands of the west. It expanded further and further east as forests were cleared and more and more land was converted to agriculture and other open habitats. Until the vast forests in the east were cleared, it is believed that they acted as a blockade, keeping the Brown-headed cowbird in the open habitats of the west. 

The Brown-headed cowbird is a brood parasite and does not build its own nest or raise its own young. Instead, the females lay their eggs in the nests of other birds. Typically they will wait patiently until the female leaves the nest unprotected and then slip in and lay their eggs. Then the unsuspected birds just follow their instincts and raise the young cowbirds as if they were their own. Unfortunately, the young cowbirds often grow more quickly then the other bird's nestlings and out compete them for food often leading to their starvation. I once watched a recently fledged Brown-headed cowbird follow around a much smaller Yellow warbler that I suspected was its surrogate parent. The size difference was amazing and there were no fledgling yellow warblers nearby leading me to believe that the Brown-headed cowbirds had out competed them for food leading to their demise.  Many scientific studies have documented the huge negative effects of this on many species of songbirds. This parasitic behavior of the Brown-headed cowbird is innate and stems from their ecology in the plains and open habitats of the west. They apparently evolved following the huge herds of buffalo and other mammals that once roamed the west. Since these herds never stayed in one place for long there wasn't time to build a nest or raise young. So, they evolved a very effective strategy that used other nests and birds as surrogate parents. When the Brown-headed cowbird made it to the east, they continued to employ these nesting strategies on the native songbird birds and their populations have likely been suffering ever since.        

Brown-headed cowbirds can be found in many of our parks and neighborhoods. They are easy to recognize. Use the Friends Online Guide to East Brunswick Parks to find some places to look for them. For more information about Brown-headed cowbirds and their fascinating life history visit the Cornell Laboratory of Ornithology website.

Published on the EB Patch, March 21, 2012


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