WEAK MATE GUARDING IN TREE SWALLOWS - ECOLOGICAL CONSTRAINT OR FEMALECONTROL

We re-examined tree swallows (Tachycineta bicolor) for the presence of the paternity protection tactic of mate guarding using less conservat ive criteria for its detection than did an earlier study. Our results are consistent with weak mate guarding, but may also be explained by t he copulatory access hypothesis. The latter hypothesis suggests that t he spado-temporal demands of pair copulation can result in a similar p attern of behaviour to mate guarding. We address two hypotheses advanc ed previously for the lack of intense mate guarding in this species as compared with other species. These are that female fidelity obviates the need for males to mate guard, and that the risk of nest site usurp ation prevents males from guarding. Since tree swallows have one of th e highest known rates of extra-pair paternity, the first hypothesis is discounted. We find the second hypothesis unlikely after an examinati on of the species' ecology, and suggest an alternative hypothesis to a ccount for the lack of intense guarding. In short, we propose that in species such as tree swallows, in which females appear to have a signi ficant degree of interest in, and control over, extra-pair fertilizati ons, frequent copulation may be a more cost-efficient means of ensurin g paternity than is mate guarding.