Plumage coloration and conspicuousness in birds: Experiments with the Pied Flycatcher

Abstract

Hypotheses concerning predation, sexual selection, and communication in birds often assume that individuals differ in conspicuousness. However, few studies have tested this by measuring the response of individuals that receive the signals. We investigated the effect of plumage coloration on conspicuousness by presenting caged Pied Flycatchers (Ficedula hypoleuca) to unmated territorial males and measuring the time until a response (either courtship or aggression) from the territorial male was observed. In the first experiment, we presented caged males and females at various distances and degrees of habitat openness. Caged birds elicited responses more rapidly in open than in closed habitats, and response time increased with distance. Black-and-white-colored males seemed to trigger a response more rapidly than brown-colored females, at least in open habitats. In the second experiment, we presented bright-colored males, dull males, and bright-painted dull males. All trials were made at the same distance. Caged birds again elicited more rapid responses in open than in closed habitats. Bright-colored males seemed to trigger a response more quickly than dull-colored males, but only in closed habitats. Painted birds elicited response times intermediate to those of bright and dull males. The difference in interaction between color and habitat in the two experiments is difficult to explain but may have been caused by differences in background related to seasonal development of vegetation. One possible problem with experiments on conspicuousness is that the response may be delayed after the receiver has detected the signal. Field observations of the behavior of territorial birds suggested that this probably did not confound the results of our study. Thus, the results support the intuitive but previously untested hypothesis that a bright and contrasting coloration makes birds more conspicuous to conspecifics.