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

The evolution of bird coloration has inspired many hypotheses. We report th e results of comparative tests involving the interacting effects of microha bitat 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 specie s subjected to high parasite "pressure" evolve showy trails that enhance th e ability of females to choose parasite free mates. We found no significant relationship between mean parasite abundance and showiness among the 122 s pecies. However, for the 66 non-passerine species in the data set, we found a significant negative relationship between parasite abundance and showine ss, contrary to the Hamilton and Zuk prediction. These results are discusse d in light of recent work on parasite-mediated sexual selection. We also te sted for a relationship between showiness and the microhabitat use of diffe rent species of rainforest birds. Like other authors, we found a significan t positive relationship between showiness and foraging stratum among the 11 3 species analysed. While drab species occur in all forest strata, showy sp ecies occur mostly in the midstorey and canopy. We discuss variables which may influence the evolution of such a pattern among forest birds.