Sexual selection, mating systems, and the evolution of avian acoustical displays

We tested the prediction that males of polygynous species with leklike mating systems exhibit convergent acoustical displays. Acoustical displays were compared among species in nine avian families having species with monogamous and polygynous mating systems. Polygynous species were more noisy, consistently used a broader range of sound frequencies, made many nonvocal sounds, and were less melodic than their monogamous counterparts. The sounds produced by polygynous males were similar to aggressive calls. These results confirm the prediction of an evolutionary convergence in courtship sound characters among species that have independently evolved polygyny. The hypothesis that male displays are not arbitrary but have important functions emerging with the evolution of polygyny is also supported. The similarity among male displays may be a result of the female use of courtship calls to assess the dominance of prospective mates.