High pair fidelity despite sex differences in the duration of parental care in a long-lived migratory bird

Abstract

In monogamous birds, pair bond maintenance is often dependent on previous breeding success and each parent’s effort, because partners gain information about one another’s quality and contribution to brood rearing. The asymmetries between mates in parental investment have been theoretically linked to a sexual conflict of interests. Year-to-year pair fidelity decisions in relation to birds’ previous-year information about their mates, including territory quality and relative length of brood care, were explored in red‐necked grebes (Podiceps grisegena), a long-lived species with parent-fed young. Overall, mate retention was a major strategy (81.5% of pair-years). The probability of breakage/maintenance of a pair bond was not affected by previous-year hatching success, fledgling production, or territory quality in terms of food abundance for chicks. Reunited pairs bred earlier in the season than new pairs. In pairs that maintained bonds into the subsequent season, females typically terminated care 1–4 weeks before males. The male fidelity indicates that earlier brood abandonment by females may confer some fitness benefits to males and reflect coordination of reproductive effort at the behavioural level rather than exploitation of one partner by another.

Significance statement

Pair-living animals deciding whether to keep their old mate for future breeding usually consider their previous reproductive success and the partner’s effort. In some monogamous birds, often one of the parents leaves the brood before its mate, which is usually explained in terms of conflict between the sexes over parental care costs. I studied links between previous year’s parental effort and mate retention in red‐necked grebes, a long-lived waterbird. Grebes showed high pair fidelity irrespective of recent breeding success. In pairs that stayed together, females typically terminated brood care earlier than their mates. The male fidelity indicates that the unequal duration of brood attendance can be interpreted as cooperation and not conflict, especially as departing females did not attempt a second brood, while male-only care after female departure was sufficient to raise the young.