Sex-Biased Pattern Variation in the Prey of Birds

Abstract

Species eaten by birds often exhibit considerable interindividual variability in their color patterns. Usually, this variability appears to have the function of protecting against avian predators (43, 96). Although both sexes are equally variable in most prey species, there have been a number of reports of species exhibiting sex-biased color pattern variability. Interestingly, the female is almost always the more variable sex. Female-biased polymorphism has been described for hundreds of species of butterflies and our survey of taxa ranging from spiders to lizards has revealed that female-biased color pattern variability is much more common than male-biased color pattern variability among avian prey species (see Table 1 at the end of the chapter). The occurrence of female-biased pattern variability is intriguing because of its patchy taxonomic distribution (e.g. it is fairly common in butterflies and lizards, but not in grasshoppers, salamanders or snakes) and because it encompasses both mimet­ ic and cryptic types of color patterns. In the present report, we investigate hypotheses which could account for the prevalence and distribution of female­ biased pattern variability among avian prey species.