Parasites represent a large fraction of the biodiversity of the earth, yet much of parasite ecology remains obscure. Most parasite studies assume that host characters are the primary, indeed, only factor influencing parasite adaptation. This research investigates the roles of other living and non-living factors that mediate host use and parasite distribution. Mourning Doves have two species of feather-feeding, ectoparasitic lice. These lice are restricted to subsections of the Mourning Dove range, but these sections are not isolated and even have some area of overlap. This project investigates how parasite-parasite interactions and an environmental character, humidity, may be restricting these parasite species to a limited geographic subset of the available hosts. Most organisms play host to multiple parasite species and the interactions between the parasite species are not well understood. This project will test how competitive interactions between different louse species affect louse community composition across the entire range of the host. Humidity levels, which are critical to the survival of many insects, vary greatly across the range of the Mourning Dove. This work will also evaluate survival of the two species of lice at low humidity. This model system is useful for parasite work because both the parasites and their hosts are easy to manipulate and keep in captivity. This work is broadly relevant to attempts to understand parasite and disease distributions in humans, domesticated animals and endangered wildlife. It also has an important training component, for one Ph.D. student and an undergraduate assistant.