Arbovirus infection is a major determinant of fitness in House Sparrows (Passer domesticus) that invade Cliff Swallow (Petrochelidon pyrrhonota) colonies

Wild birds play a key role in the amplification and transmission of many of the arthropod-borne viruses (arboviruses). Determining the extent to which birds are affected by these viruses is critical in predicting the pathogens' spread or maintenance in vertebrate host populations. Little is known about how arboviruses affect amplifying hosts' fitness, especially in cases where these viruses infect nestling birds. Buggy Creek virus (BCRV; Togaviridae: Alphavirus) is an RNA arbovirus transmitted by the Swallow Bug (Oeciacus vicarius) to Cliff Swallows (Petrochelidon pyrrhonota) and House Sparrows (Passer domesticus) that have recently occupied Cliff Swallow nesting colonies. We examined fitness, as measured by fledging success, of House Sparrows occupying Cliff Swallow nesting colonies in western Nebraska. Most nestlings naturally infected by BCRV at 4–6 days of age died, and even older nestlings, when infected, showed fledging success of