Birds such as the scarlet tanager and wood thrush may be seen around these places, but they may not be raising enough young to replenish themselves. Another serious problem is that nests near openings are more prone to cowbird predation. Often the cowbird young are larger than the warbler or host nestling. The young cowbirds are aggressive and demand the most food from the host parents. The young warblers may starve to death while the cowbird young survive.
Cowbird parasitism is a serious threat to many songbirds.
In contrast, nests located in deep woods are less susceptible to cowbird predation. Cowbirds, by the way, used to follow the American bison over the prairies, picking up grubs and worms from dung. It is suspected that cowbirds developed their parasitic habits because of their nomadic behavior of following the roving herds of bison. Bison once lived in West Virginia. Not all neotrops in West Virginia are birds of the deep woods.