Courtship feeding in Ospreys Pandion haliaetus: a criterion for mate assessment?

Abstract

In many bird species males provision their mates prior to egg‐laying. Courtship feeding has been suggested to function in several ways: to advance laying date by improving female condition, to induce a female to copulate or to allow a female to assess her mate. The role of courtship feeding in Ospreys Pandion haliaetus was investigated in British Columbia, Canada. Courtship feeding rate affected the probability of a pair initiating a clutch. Pairs that laid eggs had higher rates of courtship feeding than pairs that did not lay eggs in both 1991 and 1992. Male courtship feeding rate also correlated negatively with the duration of the courtship period. Experimentally increasing the amount of food available to females prior to egg‐laying resulted in a nonsignificant reduction in the duration of the courtship period. This study found no evidence to support the suggestion that female Ospreys trade copulations for food during the courtship period; only 63 of 385 copulations observed were associated with feeds, and courtship feeding rate did not correlate with the copulation rate of a pair. Male provisioning rates, however, were predictable; courtship feeding rate correlated with both male delivery rate to the nest when chicks were 1–2 weeks old and mean brood growth rate. Female Ospreys therefore may be able to predict the quality of subsequent paternal care using courtship feeding rate. As predicted if optimal hatching asynchrony is dependent on food availability, mean brood growth rate, an indirect measure of male parental care, was negatively correlated with hatching asynchrony. This suggests that female Ospreys may manipulate hatching asynchrony in response to male courtship feeding rate, thereby maximizing the productivity of their brood at predicted food levels.