Ectoparasitism as a Cause of Natal Dispersal in Cliff Swallows

Abstract

Nestling Cliff Swallows (Hirundo pyrrhonota) in southwestern Nebraska that were relatively heavily parasitized by hematophagous fleas (Ceratophyllus celsus) and swallow bugs (Oeciacus vicarius) dispersed to nonnatal colonies to breed the subsequent year, whereas nestlings that were relatively lightly parasitized returned to their natal colony to breed. There were no significant differences between dispersers and nondispersers in natal clutch size, natal brood size, relative hatching date, natal body mass, natal nest's distance from the colony's center, and natal nest's age. There were no sex differences in dispersal tendencies. Dispersing birds tended to move to smaller colonies to breed, and in some cases settled in breeding colonies later than nondispersers. Ectoparasitism may be a major cause of natal dispersal in Cliff Swallows and perhaps should be considered another potential cause of dispersal in general, especially in group—living species that may be associated with large numbers of highly co—evolved ectoparasites.