HIGH PARASITE LOAD IN-HOUSE FINCHES (CARPODACUS-MEXICANUS) IS CORRELATED WITH REDUCED EXPRESSION OF A SEXUALLY SELECTED TRAIT

Independent of age or geographic variation, males of many species of b irds exhibit dramatic variation in the expression of elaborate seconda ry sexual characters. ''Good genes'' models of sexual selection propos e that males with relatively low resistance to parasites suffer high p arasite loads that inhibit their ability to express these characters f ully. In turn, variation in such characters may reliably indicate male quality and may be used by females to choose males. This is the first study to monitor (via mark-recapture) the long-term effects of parasi tes on color and growth of plumage in individual birds. Specifically, we used house finches, Carpodacus mexicanus, a sexually dimorphic spec ies in which females are known to prefer more brightly plumaged males for mating, to test the hypothesis that high parasite load in males is correlated with poor physiological condition and reduced development of male secondary sex characters. Our results clearly demonstrate that both ectoparasitic feather mite (Proctophyllodes sp.) infestations an d endoparasitic avian pox viral infections during molt are correlated with poor physiological condition and reduced development of bright ma le plumage during the same molt period, thus supporting good genes mod els.