Why don't female purple sandpipers perform brood care? A removal experiment

In most monogamous sandpiper species, females share parental care but leave the brood earlier than males, a feature unusual among birds in general. In the purple sandpiper (Calidris maritima), females almost always leave the brood at hatching and never share brood care. Males perform uniparental brood care from hatching until well after fledging. In this paper, we report the results of a mate-removal experiment conducted on the purple sandpiper in high Arctic Svalbard and discuss the implications for the evolution of their mate desertion strategy. By removing males from nests near hatching, we tested 2 hypotheses: 1) Males assume brood care because females, who always have a net benefit from deserting, have a fixed brood desertion strategy, whereas males do not; 2) females desert the brood because they cannot perform uniparental brood care as well as males and/or because they are under physiological stress at hatching due to egg laying and incubation activities hypothesis). We found that when experimentally deserted, most female purple sandpipers assumed brood care. Parental behavior and the growth and survival of the chicks suggested that the attending females were not under physiological stress after hatching and did not seem less able than males to perform brood care. Thus, we found no support for either hypothesis. We suggest that uniparental brood desertion is a consequence of strong selection for uniparental brood care in this species and that the actual sex roles may result from rather marginal differences between the sexes in the fitness consequences of care and desertion. Copyright 2010, Oxford University Press.