Physically challenging song traits, male quality, and reproductive success in house wrens.

Emily R A Cramer,Gabriele Sorci

doi:10.1371/journal.pone.0059208

Abstract

Physically challenging signals are likely to honestly indicate signaler quality. In trilled bird song two physically challenging parameters are vocal deviation (the speed of sound frequency modulation) and trill consistency (how precisely syllables are repeated). As predicted, in several species, they correlate with male quality, are preferred by females, and/or function in male-male signaling. Species may experience different selective pressures on their songs, however; for instance, there may be opposing selection between song complexity and song performance difficulty, such that in species where song complexity is strongly selected, there may not be strong selection on performance-based traits. I tested whether vocal deviation and trill consistency are signals of male quality in house wrens (Troglodytes aedon), a species with complex song structure. Males’ singing ability did not correlate with male quality, except that older males sang with higher trill consistency, and males with more consistent trills responded more aggressively to playback (although a previous study found no effect of stimulus trill consistency on males’ responses to playback). Males singing more challenging songs did not gain in polygyny, extra-pair paternity, or annual reproductive success. Moreover, none of the standard male quality measures I investigated correlated with mating or reproductive success. I conclude that vocal deviation and trill consistency do not signal male quality in this species.

Highlights

In species with traditional sex roles, intrasexual selection favors male traits that enhance their ability to out-compete other males for mating opportunities, and intersexual selection favors traits that make males more attractive to females [1]
Signal complexity may be under strong selection (e.g., [7]), and there may be divergent selective pressures such that species selected to have more complex songs are not under selection for performance-based signals, while species with strong selection on performance-based signals may not be under strong selection for signal complexity [8]
Vocal deviation and consistency are two aspects of song that have recently received a great deal of attention as potential honest signals of male quality, because they appear to represent challenging motor displays

Summary

Introduction

In species with traditional sex roles, intrasexual selection favors male traits that enhance their ability to out-compete other males for mating opportunities, and intersexual selection favors traits that make males more attractive to females [1]. Birds’ songs are elaborate signals that probably represent a substantial motor challenge because they involve coordinating movements of the respiratory system, the vocal organ (the syrinx), and the upper vocal tract [9,10]. As such, they have been extensively studied with regard to honest signaling [7,11]. Vocal deviation and consistency are two aspects of song that have recently received a great deal of attention as potential honest signals of male quality, because they appear to represent challenging motor displays

Results

Discussion

Conclusion