Grays Harbor Birds — Brown-headed Cowbird


This is a bird a lot of people love to hate, and I am sure many are wondering why I would even bother covering it in this venue — it’s an interesting bird. Brown-headed Cowbirds are fairly recent arrivals to our state, or at least during breeding season, only being counted here as breeders since 1958.

Development and forest fragmentation have encouraged new territories and new host species for their nesting habits and as a result, there has been a significant impact on some of their more common hosts. They are considered one of the more important causes of songbird decline in North America; a bad rap indeed. Gregg Thompson’s photo shows a male.

Size: 7.5 inches long, with a wingspan of 12 inches, and weighing 1.5 ounces.

General Description: The adult male Brown-headed Cowbird has a glossy black body with a dull brown head; first-year males are a dull black, and females are much smaller, with brown bodies, a pale throat, and light streaking on their breast and belly. The cowbirds bill is a conical shape, more like a finch. The cowbirds main claim to fame is its habit of laying eggs in the nest of other birds.

Habitat: Cowbirds are most often found at edge areas, where they forage in open areas and breed in scattered trees in open woodlands. Their favorite types of habitat are streamside thickets and woods near agricultural fields, lawns in parks, and housing developments with scattered trees. Humans have increasingly made such areas readily available as we clear forests and build houses.

Behavior: Brown-headed Cowbirds are mostly ground feeders, so where they once probably followed herds of bison picking up food churned up by all the hoofs, they now follow cattle, horses, and sheep for the same reason. They can also be found lurking in trees and bushes watching for a chance to parasitize any nests.

Diet: During the summer, the cowbirds’ diet is half seeds, half insects and other invertebrates. Females also eat eggshells and mollusk shells, especially during the breeding season when they need a lot more calcium to produce the number of eggs they lay. In the winter, more than 90 percent of the diet is made up of seeds and waste grain, hence the likelihood of finding cowbirds near grain storage areas.

Nesting: Brown-headed Cowbirds never build nests or raise their own young. Generally monogamous, males arrive on the breeding grounds before the females and scout for other nesting birds in nearby territories. The female then helps to find likely nests, and they both fly back and forth in noisy flights to flush potential hosts. The female then chooses an open-cup nest which already contains at least one egg, removes one of the host eggs, and lays one egg per nest, laying up to 40 eggs in a season. Incubation time is a short 10 to 12 days, allowing the young cowbird to get a competitive edge over the hosts babies. Young cowbirds leave the nest after 8 to 13 days but the host parents continue to feed them until they are anywhere from 25 to 39 days old, often to the detriment of their own nestlings. At least 144 species raise cowbird young to the fledgling stage.

Migration: Brown-headed Cowbirds are generally short to medium-distance migrants, only migrating to feed-lot areas in our state. They often migrate in flocks with other blackbird species.

Conservation Status: Cowbirds are common and widespread throughout Washington, although there has been a significant decline since 1966, which is good news for those species being parasitized such as the Song Sparrow and the Yellow Warbler, the two most often victimized.

When and Where to Find on Grays Harbor: Brown-headed Cowbirds are generally summer residents in open fields and lawns, and in areas where there is loose grain or grain being stored, such as feedlots, from mid-April through September. There are some that over-winter but most head east of the Cascades, or up into the Puget Trough. And, we are glad!

 

Rules for posting comments