Cw. Thompson et al., HIGH PARASITE LOAD IN-HOUSE FINCHES (CARPODACUS-MEXICANUS) IS CORRELATED WITH REDUCED EXPRESSION OF A SEXUALLY SELECTED TRAIT, The American naturalist, 149(2), 1997, pp. 270-294
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.