The Brown-Headed Cowbird
Parasite In Your Backyard
Many people are somewhat selective about which birds they want to feed in their backyard. Some put out certain seeds to attract or deter certain birds or use feeders for the same purpose. Caged feeders for instance will keep out the larger "bully" birds and spherical feeders only attract those clinging birds.
I've always tried to attract and feed as many birds as I can. Even when I complain about the scores of blackbirds wiping out an entire supply of food, it is more in the tone of good-natured complaining. Everybody is welcome.
But if there is one bird who should be banned from feeders, it is the brown-headed cowbird. A brown-headed cowbird is one of those great numbers of black birds that swoop into a yard with great commotion to diminish the supply of food for the rest of the "deserving" birds. However, the brown-headed cowbird is more wicked than this. The cowbird practices brood parasitism.
The parasitism practiced by the brown-headed cowbird is quite ingenious and remarkable to behavioral scientists. The female cowbird lays her eggs in other birds' nests. The cowbird is the only species of bird in North America to do this.
When other birds are finished building nests and have are about to lay (or have just laid) eggs, the cowbird lays one egg in the nest. Two would make the other mother suspicious. Only one egg is laid in a nest of usually a smaller species. When the egg hatches, the other mother not only takes care of the baby cowbird as her own, but since the cowbird is larger, he can usually compete successfully for the larger share of food. In many cases, the cowbird survives, while the victim babies do not.
Being raised and growing up with another species does not seem to effect the cowbird's ability to act and live like a cowbird for the rest of its life. So much for the "ugly duckling" story.
According to the "Sibley Guide to Bird Life and Behavior" the cowbird has over 200 species that it uses as victims throughout its range. In the Southeast and Northern Florida, thrushes and warblers are frequent victims. In the backyard, the two favored victims are the northern cardinal and the painted bunting.
In the past years, there has been a real decline in the number of painted buntings and habitat loss is the most often cited reason for this decline. However, a significant factor in the loss of painted buntings is brood parasitism by the cowbird.
The male brown-headed cowbird is pretty easy to identify, being a black bird slightly smaller than a robin, with a brown head. It's a lot easier to identify the female when she is feeding with the male. She is a light grey to beige color, not black at all.
In the backyard not only does the brown-headed cowbird's nesting habits endanger the cardinal and the painted bunting, but it also loves the same food. Many of us put our white millet seed in a tube feeder for the painted buntings. Larger birds have a harder time perching and eating out of a tube feeder. Not the cowbird. He can sit on a small perch and eat much easier than other larger birds.
A caged feeder might be the solution, if the buntings can be coaxed into using it.
But next time you fill your tube feeder with white millet, put up a sign: "for Painted Buntings only".