Contrast influences female attraction to performance-based sexual signals in a songbird.

Animals do not make decisions in a bubble but often refer to previous experience when discriminating between options. Contrast effects occur when the value of a stimulus affects the response to another value of the stimulus, and the changes in value and response are in the same direction. Although contrast effects appear irrational, they could benefit decision makers when there is spatial or temporal variation and autocorrelation in the value of stimuli that elicit decisions. Here, we examined whether contrasts influence female evaluation of male performance-based sexual signals. We exposed female Lincoln's sparrows (Melospiza lincolnii) to one week of songs that we had experimentally reduced or elevated in performance, followed by a novel song of intermediate performance. We found that high-performance songs were more attractive to females than low-performance songs. Moreover, the intermediate songs were more attractive following exposure to low- than to high-performance songs. These results indicate that contrast can influence evaluation of performance-based sexual stimuli. By examining contrast effects in the ecologically relevant context of mate choice for performance, we can better understand both the adaptive value of comparative evaluation as well as the mechanisms that underlie variation in mate choice and sexual selection.