Meeting Abstract

P1.32  Thursday, Jan. 3  A Comparative Study of Color Variation in the Juvenal Plumage of Terns (Sternini) PHILLIPS, J. L.*; CRAIG, D. P.; Lewis and Clark College; Willamette University jenp@lclark.edu

Terns form a subfamily of birds, Sternini, that exhibits a conspicuous amount of variation in juvenal plumage. In this study we quantified the amount of color variation found in this plumage and compared it to natural history traits in a phylogenetic context. We photographed 600 study skins from 25 species. For each bird, we calculated percent area covered by 6 colors and used these areas to give an index of color variation within each species. We compared this variation index to previously published natural history traits on the species level using phylogenetic methods. Using concentrated changes we found that nesting on bare earth was significantly related to the subsequent increase of the variation index in character state reconstructions. Using independent contrasts we found a positive correlation between internest distance and the coloration index. Greater color variation in species that nest on bare ground could be caused by selective pressure for camouflage on variably colored substrates coupled with rapid colony turnover. A possible explanation for species that nest closer together having less color variability could be neighboring parents being less aggressive toward chicks that are less visibly distinct from their own. On the individual level, we tested for correlations between both latitude and year of collection with individual color values of individual specimens. Year of collection was correlated with color values in nine species; latitude was correlated with color values in nine species. Fading and changing taxidermic practices could cause the correlations between color values and year. Humidity and temperature gradients could produce the patterns we found between color values and latitude. We hope that this study will prompt further investigation of the patterns found.