The bird of the month for April is the Brown-headed Cowbird.

Molothrus ater

     Once known as "Buffalo bird", the Brown-headed Cowbird now attends livestock, inhabits fields,  farmlands and backyards. It is approximately 7 1/2" long with a stubby, conical bill and relatively short tail. The male is glossy black with a brown head. Females are smaller and a dull greyish brown color. Juveniles are similar but streaked below. The male’s song is a squeaky gurgling, usually ending with a few high, squeaky whistles. The female’s chatter is often given in unison with the male’s song during courtship. Calls include a harsh rattle or chatter, usually given by the female, a short chuck note given by both sexes when alarmed, and squeaky whistles given by the male, especially in flight. The loud begging calls of fledgling cowbirds are distinctive.They are abundant birds in nearly all of North America.
 

     For most birders the cowbird strikes fear in their hearts for it is best known for parasitising the nests of other species. It does not build it's own nest; rather it deposits it's eggs in other bird's nests, especially those of flycatchers, warblers, finches and vireos. It has actually been recorded as a parasite of more than 200 other species. They do not raise their own young but leave that up to their hosts. The Cowbird eggs do not usually mimic the host eggs in appearance nor do the young push out the host eggs and young from the nest as some other parasitic birds do such as the European Cuckoo. But Cowbirds do tend to hatch earlier than their hosts, grow faster, and crowd out or at least reduce the food intake of the host's young.
 

     Of deep concern is their parasitising the nests of endangered species like the Kirtland's Warbler which is found exclusively here in Michigan  in only six counties. Cowbirds have been abundant in Kirtland's habitat only recently as forests in the area were cleared for agriculture. The warblers are not adapted to defend against them. The percent of parasitized nests increased from about 55% in the 1940's and 50's to over 70% in the 1960's.
It is an especially dangerous enemy because of the fact that it parasitizes numerous species and is therefore not dependent on Kirtland's Warbler. As it reduces the warbler population, its own population size will not necessarily decline- its assault can be unrelenting. Thus when the decline in warbler populations was observed, the U.S. Fish and Wildlife Service along with several state agencies and the Detroit and Pontiac Audubon Societies began a program of trapping and removing cowbirds. By about 1980 over 40,000 cowbirds had been removed, and as a result the level of parasitism of warbler nests became negligible. Kirtland's fledging rates have tripled, so that their nesting success is now higher than that known for any other warbler. By 1977 the decrease in warblelr numbers had clearly been halted and 219 singing males were counted.
     The future of Kirtland's warbler remains in doubt however. Even with  the cowbird control program, more conservation methods are needed if the species is to be saved. The only long-range solution is to maintain enough habitat in Michigan for them to persist without constant human interference and keeping their West Indian wintering grounds in suitable condition.