Adirondack Forest and Brown-headed Cowbirds

The Brown-headed Cowbird is a brood parasite that lays eggs in the nests of other birds for the host species to raise. The cowbird has been observed to lay its eggs in the nests of more than 220 host species in North America. Brood parasitism by the cowbird is one of many recent disturbances believed to contribute to the decline of North American songbirds.

The brown-headed cowbird is formerly a prairie species that followed bison migrations. The colonization of North America by European settlers, their westward expansion and destruction of virgin forests has contributed to a rapid eastward spread of cowbird populations. This expansion has allowed cowbirds to parasitze nests of forest bird species because forests are now fragmented between field, meadows, and open areas where cowbirds forage. One solution to managing cowbird populations may be to increase the size of forest plots where cowbirds are unable to parasitize nests deep within the forests. Such is the case and plans for ecologists and ornithologists in southern Illinois.

Earlier today, I examined the 2000-2005 breeding bird atlas for the brown-headed cowbird in New York State. The following graph shows that the cowbird is largely absent from the Adirondack region. Despite an ample supply of host species (warblers, thrushes, vireos, sparrows, and flycatchers) in the ADK, the numbers of putative breeding cowbirds is very low. Perhaps this is one of many favorable ecological consequences of land management practices in the Adirondacks. The large tracks of land with pristine forests limit access to brown-headed cowbirds and, therefore, reduce the negative effects of brood parasitism.