SELECTION OF HIGH-QUALITY HOST NESTS BY PARASITIC CLIFF SWALLOWS

Parasitic cliff swallows, Hirundo pyrrhonota, in southwestern Nebraska nest in dense colonies where an individual has many potential host nests it can parasitize. Parasites apparently assessed the nests around them and used nest age early in the season as a cue to select the more protected host nests. Swallows that parasitized nests later in the season, with a longer time to assess their neighbours, preferentially selected nests that were eventually successful at producing fledglings. Parasitic cliff swallows at all stages tended to select host nests that ultimately had the lowest infestations of deleterious, blood-sucking ectoparasites. This represents the first evidence that birds that parasitize conspecifics can make fine-scale assessment of a nest's quality and choose the better of the available nests in which to place their parasitic eggs. © 1991.