PARASITE FAUNAS, TESTOSTERONE AND SECONDARY SEXUAL TRAITS IN MALE RED-WINGED BLACKBIRDS

We examined associations among parasite infections, secondary sexual t raits and testosterone in male red-winged blackbirds sampled at the st art of the breeding season. Parasites quantified included ectoparasiti c lice and mites and endoparasitic blood protozoans, nematodes, tremat odes and cestodes. Secondary sexual traits that we quantified included body size, epaulet size and color, song repertoire size and song swit ching rate, and behavioral responses to male and female models. Overal l we found few significant associations between parasites and secondar y sexual traits, between secondary sexual traits and testosterone, or between parasites and testosterone. In addition, most parasite taxa ap peared to infect birds independently, although the low prevalence (< 5 0%) of many of the parasites meant that our sample sizes were too smal l to detect weak associations. Our most promising results were obtaine d for ectoparasitic mites, which tended to occur on birds uninfected w ith other parasites, on birds with longer epaulets, and on birds with higher levels of testosterone. Epaulet length and testosterone are bot h probable correlates of dominance in this species. Further research w ill be required to determine whether there is a causal link between th e immunosuppressive effects of testosterone and the mite infections, a nd between testosterone, epaulet length and male mating success.