The preening activity of swallows, Hirundo rustica, in relation to experimentally manipulated loads of haematophagous mites

Whether differences in preening activity among breeding swallows might be a reliable predictor of infection rates by the haematophagous mite Ornithonyssus bursa was tested by recording preening during an experimental manipulation of mite population density. Mite populations of newly built nests were either decreased by spraying with a pesticide, or increased by inoculation with ca 50 mites, while other nests were kept as controls. Adult swallows did not alter their preening rates in relation to experimental treatment despite the fact that the experimental treatments strongly affected mite densities. Nestlings raised in nests inoculated with mites preened much more than did control nestlings, which preened more than did nestlings from sprayed nests. Individual swallows had consistent preening rates throughout the breeding season. Male swallows preened more than females, and male preening activity was strongly positively correlated with that of their mates. Swallows preening much during their first clutches maintained a high preening frequency during their second clutch, although there was a general seasonal decrease in preening rates. Swallows rearing two broods preened more than did pairs rearing only a single brood.