Links Between Lice Species, Cowbird Fledglings, and Avian Host Species

Cowbirds lay their eggs in songbird nests, replacing some songbird eggs with their own; the unwitting songbirds end up raising cowbirds. Biologist Caldwell Hahn at the Patuxent Wildlife Research Center in Maryland is trying to find out which songbirds raise the most cowbirds. She could have tediously observed the nests of hundreds of songbirds to see which species were targeted most often. But she realized the cowbirds would pick up lice that infest songbird feathers and that perhaps she could examine lice on songbirds and cowbirds to identify those species the cowbirds victimize. She and her colleagues caught 797 songbirds of 30 species and 249 cowbirds. They placed each bird in a jar containing ethyl acetate, which kills the bugs but not the birds. Hahn has already found a kind of louse that parasitizes mainly sparrows and another that prefers wood thrushes; both were among the 12 species found on cowbirds. The preliminary results indicate that certain species of louse tend to be associated with certain species of host and that these lice can be used as indicators of the host that raised the cowbirds.