Whatʹs bugging brood parasites?

Brown-headed cowbirds (Molothrus ater) might reduce populations of the songbird species they parasitize, including endangered species. Data are therefore needed on the frequency with which cowbirds use different species of foster parents. Hahn et al. propose a clever new approach by which the identity of foster parents can be inferred from host-specific lice the cowbirds acquire as nestlings. We discuss the feasibility of this method and underlying assumptions.