Nest mites (Pellonyssus reedi) and the reproductive biology of the house finch (Carpodacus mexicanus)

We investigated the effects of a hematophagous nestling mite (Pellonyssus reedi, Acari: Macronyssidae) on the reproductive biology of the house finch (Carpodacus mexicanus) in east-central Alabama, U.S.A. Mites were absent from nests for the first half of the breeding season, but after their initial appearance they increased in number and were present in almost all nests. High nest-mite levels were associated with decreased nestling mass and hematocrit, but not with decreased nestling tarsus length. Experimental elimination of mites from some nests confirmed that the effects observed were mite-induced, not seasonal. The plumage colour of breeding adult male house finches was not correlated with nest-mite levels, nor did it appear that redder males' offspring suffered less from the effects of mites. Adult house finches fed nestlings from highly parasitized nests less often than those from nests with few or no mites. It appears unlikely that mites are directly involved in the sexual selection of bright male plumage coloration in this population of house finches. However, it is known that early-nesting females preferentially pair with redder males, therefore the benefit of nesting early and avoiding mite infestations is greater for redder male house finches.