Knowledge of globally threatened biodiversity is the key to its maintanance. Costa Rica contains more animal and plant species than any other country of the equal size. In total, 903 bird species have been recorded from the country. Various ectoparasites are associated with them, including chewing lice (Phthiraptera: Amblycera, Ischnocera) and mites. Data concerning those parasites are scarce and incomplete. Based on our recent studies of ectoparasites on birds in the Neotropical Region at lower elevations of the Caribbean slope, Costa Rica, and in the Cerrado biome of Brazil, ectoparasites on birds in mountain areas of Costa Rica will be studied. The species diversity, prevalence, and infestation intensity of chewing lice as well as ectoparasitic Acari (Trombiculidae, Ascidae, Ixodidae) in birds species inhabiting Costa Rican mountain ecosystems will be characterized. Host-parasite associations will be studied and species new to science described. Type material will be deposited in Costa Rican INBio and other museums. Moreover, morphological and genetic variation within the genus Menacanthus as well as within the populations of M. eurysternus, extremely euryxenic and cosmopolitan species, will also be studied. Both morphological and genetic data will be used to reconstruct phylogeny of this group of chewing lice.