Showiness of Neotropical birds in relation to ectoparasite abundance and foraging stratum

The evolution of bird coloration has inspired many hypotheses. We report the results of comparative tests involving the interacting effects of microhabitat use, sexual selection and parasite transmission on colour evolution. We used a data set of chewing lice (Insecta: Phthiraptera) sampled from 122 Neotropical bird species to test Hamilton and Zuk's prediction that species subjected to high parasite 'pressure' evolve showy traits that enhance the ability of females to choose parasite free mates. We found no significant relationship between mean parasite abundance and showiness among the 122 species. However, for the 66 non-passerine species in the data set, we found a significant negative relationship between parasite abundance and showiness, contrary to the Hamilton and Zuk prediction. These results are discussed in light of recent work on parasite-mediated sexual selection. We also tested for a relationship between showiness and the microhabitat use of different species of rainforest birds. Like other authors, we found a significant positive relationship between showiness and foraging stratum among the 113 species analysed. While drab species occur in all forest strata, showy species occur mostly in the midstorey and canopy. We discuss variables which may influence the evolution of such a pattern among forest birds.