Brood care in American robins: Implications for mixed reproductive strategies by females

Parental care of nestling and fledgling American robins, Turdus migratorius, was studied in eastern Ontario. There was no evidence of brood division prior to fledging but brood division was the predominant pattern after fledging. Females initiating second nests reduced their care of fledglings sooner than males. Once incubation began at second nests, males provided all the care for fledglings from the previous nest. A consequence of overlapping first and second nesting efforts is that care of fledglings from the first nest allows males little opportunity of mate guarding when their mates are initiating the second nest. Reduced opportunity for mate guarding is probably excerbated by the wide dispersal of fledglings at the time of egg laying at second nests. In spite of the apparent reduced opportunity for mate guarding, males fed nestlings in second nests as much as those in first nests. This result suggests that females initiating second nests may refrain from extra-pair copulations if their mates have proven themselves by the success of the first nest, because confidence of paternity ensures male parental care at the second nest. Information from the literature suggests that the mixed strategy by females of being willing to engage in extra-pair copulations when initiating first but not second broods may occur in other species with overlapping broods.