Bronzed cowbirds are with us for the summer
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Bronzed cowbird
By late spring in South Texas, bronzed cowbirds increase in number and become regular visitors to our yards and feeders. But they can easily be confused with the far more abundant brown-headed cowbirds that became commonplace since the first cardinals began singing in spring.
The bronzed cowbird, once known as the red-eyed cowbird because of their red eyes, is somewhat larger than their cousins, the brown-headed cowbird. Male bronzed cowbirds also possess a thick ruff on their nape, giving them a hunchback appearance. They lack the brownish head of the brown-head and are purplish or bronze colored. During courtship, the male bronzed throws back its head and erects its large ruff, quivering its wings and bouncing up and down - all the while singing a high-pitched, creaky song as it circles its ladies.
Both of these cowbirds have the habit of laying their eggs in other birds' nests, where the foster parents will raise the larger, faster-growing cowbird babies as their own. The larger cowbird young oftentimes shove the rightful nestlings out of the nest, where they usually die, and if that doesn't occur, the cowbird nestling is so much larger and aggressive that it gets the bulk of the food brought to the nest. This parasitic habit can produce severe declines in certain preferred host species. While brown-headed cowbirds parasitize such birds as gnatcatchers, vireos and warblers, including the endangered black-capped vireo and golden-cheeked warbler, bronzed cowbirds seek slightly larger birds, such as thrashers, tanagers and orioles. Hooded orioles, for example, have declined in number in several South Texas areas where populations of bronzed cowbirds have increased in recent years.
Brown-headed cowbirds are with us year-round, congregating in huge flocks in our pastures and fields during the winter months and pairing up in early spring. Most bronzed cowbirds move farther south for the winter months; the greatest numbers of bronzed cowbirds anywhere in the United States are recorded on the annual Kingsville Christmas Bird Count.
They begin pairing in late winter or early spring, about the time the earliest thrashers begin to sing and preparing to nest. And post-breeding bronzed cowbirds become more numerous and appear in our yards soon after they have mated and parasitized their neighbors.
While brown-headed cowbirds evolved on the Great Plains, where they fed on seeds among the herds of bison or on ticks on those huge beasts, bronzed cowbirds appeared from south of the border. Invaders to Texas and Arizona only since the early 1900s, bronzed cowbirds now can be found throughout most of Texas during summer. And like their smaller cousins, they are opportunists that can take advantage of a wide array of hosts, including such unexpected birds as mockingbirds and mourning doves. Only cardinals seem to be sufficiently aggressive to consistently keep these parasitic newcomers at bay.
Ro Wauer writes about nature for the Victoria Advocate. Contact him in care of Victoria Advocate, P.O. Box 1518, Victoria, TX 77902.
