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Brown-headed Cowbird Nestling

Posted on Jul 11, 2016

This spring and summer seem to have been very successful for the Brown-headed Cowbird. I realize that this is largely anecdotal, but I have had and heard a lot of sightings and stories about various species discovered feeding a hatchling or fledgling Cowbird. From the American Redstart to the Chipping Sparrow, the Yellow-throated Vireo or the Yellow Warbler, an Orchard Oriole and a Common Yellowthroat, a Blue-winged Warbler or this nest that I found and photographed a couple of weeks ago, it has been Cowbirds here, there, and everywhere. What’s the common thread? All of these birds and their nests were in open habitats or along the edge of a forest, like this Red-eyed Vireo pair.

Brown-headed Cowbird nestling Red-eyed Vireo nest-6085

Brown-headed Cowbird nestling Red-eyed Vireo nest-6100

It was very dark and I had to crank the ISO way up – even then it was tough to capture them at any appreciable shutter speed. Despite the shade and subtle placement this pair was not far from a residential neighborhood and along a stream, a far too popular and susceptible place to make a bird home. The female Brown-headed Cowbird found them, but they did not find the egg she placed in their nest. Brood parasites depend on other avian parents to raise their young, and the Cowbird young grows larger and faster than it’s would be siblings, outcompeting them for food and usually dooming all of the actual hatchlings of the pair if the eggs were not already destroyed. That is why female Cowbirds choose bird hosts that have smaller eggs than their own.

This process saves a lot of work for the Brown-headed Cowbirds responsible for bringing this egg into the world, and it also helps them spread their young to many different “baskets” for increased success. It is said that at least part of the reason Cowbirds chose this reproductive method was their nomadic lifestyle in the grasslands of North America following bison, and now they have successful utilized our changed world – from bird feeders to livestock and destroyed and fragmented woodlands. I am always particularly frustrated to see a bird like the Red-eyed Vireo making a long journey back to us all the way from South America only to raise a Cowbird. Let’s hope this pair successfully returns to the Amazon and can join us again in 2017 to fledge their own families.

Scott Kruitbosch
Conservation & Outreach Coordinator