Subtle benefits of cooperation to breeding males of the Red-backed Fairywren

Abstract

Cooperative breeding is a phenomenon whereby breeding and nonbreeding individuals collectively provision young. Nonbreeding group members ("helpers'') may gain indirect and/or direct fitness benefits by breeding in a group, but there has been conflicting evidence regarding the benefits to breeders. In fact, the presence of helpers may sometimes be detrimental to aspects of breeder fitness. For example, in some species of the chiefly Australian genus Malurus, breeding males with helpers have lower within-pair paternity than do males without helpers. Additionally, indirect benefits to breeding males are often limited by low relatedness to their helpers due to high extrapair paternity rates, and helpers often appear to have minimal impact on breeder reproductive success. However, the presence of helpers may allow breeding males to shift their behaviors from guarding and provisioning young to alternative behaviors that affect other components of fitness, such as extraterritory forays (which might increase extrapair mating success) and self-maintenance (which might increase survival). We investigated these possibilities in the facultatively cooperative Red-backed Fairywren (Malurus melanocephalus). Males with helpers spent significantly less time engaging in guarding behaviors and provisioning of young than did those without helpers, but there was no difference in the frequency of extrapair forays nor the number of young sired by males with vs. without helpers. Additionally, the decreased investment in nesting behaviors did not result in consistently higher survival, but may have increased survival in some years. Overall, the results of this study did not suggest any strong direct fitness benefits to breeding males, which may indicate that the costs of retaining helpers are negligible relative to the indirect benefits of helping a potentially related male.