Why Mated Songbirds Sing So Much: Mate Guarding and Male Announcement of Mate Fertility Status

Abstract

Fitness loss among males as a result of cuckoldry is often large, and a number of paternity guards have evolved in response to the presence of cuckoldry risks. Paternity guards such as mate guarding protect the paternity of males but also indirectly announce the fertility status of the guarded female. When such "involuntary" fertility cues have arisen, the negative effects of the cues can be ameliorated either by modifying the paternity guard or by direct announcement of female fertility. Male announcement is a reliabile indicator of male quality, if the degree of mate fertility announcement depends on male phenotypic quality and the quality of his resources, and if costs of announcement are relatively higher for low- than for high-quality males. Cuckolder males would then maximize their reproductive success by preferentially intruding during female fertility on sites with little announcement. Intensive announcement of female fertility will be a phenotype-limited evolutionarily stable strategy (ESS), since benefits continue to accrue to males relative to their investment in announcement. If male announcement rate is an honest measure of male quality, neighboring females are predicted to choose males with a high announcement rate as extrapair copulation partners. Similarly, the interest taken by a male's own females in neighboring males should be inversely related to that male's announcement rate. Sexual selection should therefore drive the announcement strategy. Information on song activity in male passerine bird species provides empirical support for the model.