Influence of host ecology and morphology on the diversity of Neotropical bird lice

Host-parasite systems can be powerful arenas in which to explore factors in fluencing community structure. We used a comparative approach to examine th e influence of host ecology and morphology on the diversity of chewing lice (Insecta: Phthiraptera) among 52 species of Peruvian birds. For each host species we calculated two components of parasite diversity: 1) cumulative s pecies richness, and 2) mean abundance. We tested for correlations between these parasite indices and 13 host ecological and morphological variables. Host ecological variables included geographic range size, local population density, and microhabitat use. Host morphological variables included body m ass, plumage depth, and standard dimensions of bill, foot and toenail morph ology, all of which could influence the efficiency of anti-parasite groomin g. Data were analysed using statistical and comparative methods that contro l for sampling effort and host phylogeny. None of the independent host vari ables correlated with louse species richness when treated as a dependent va riable. When richness was treated as an independent variable, however, it w as positively correlated with mean louse abundance. Host body mass was also positively correlated with mean louse abundance. When louse richness and h ost body mass were held constant, mean louse abundance correlated negativel y with the degree to which the upper mandible of the host's bill overhangs the lower mandible. This correlation suggests that birds with longer overha ngs are better at controlling lice during preening. We propose a specific f unctional hypothesis in which preening damages lice by exerting a shearing force between the overhang and the tip of the lower mandible. This study is the first to suggest a parasite-control function of such a detailed compon ent of bill morphology across species. Avian biologists have traditionally focused almost exclusively on bills as tools for feeding. We suggest that t he adaptive radiation of bill morphology should be reinterpreted with both preening and feeding in mind.