Courtship Feeding and Osprey Reproduction

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Abstract
A female Osprey (Pandion haliaetus) usually is fed exclusively by its mate between pair formation and egg-laying. Laying dates and courtship periods-but not clutch size, egg size, breeding success, or female weight reserves-were correlated (negatively) with the prelaying feeding rates of 12 females breeding in a coastal Massachusetts colony. However, the age of a pair and of its bond influenced laying dates and courtship periods more than food intake. Older and more experienced pairs arrived earlier and laid eggs more quickly than younger pairs. As an independent test of food limitation in Ospreys producing eggs, supplemental food was provided to 4 nests during courtship. Supplemental food did not influence a female's reproductive output or timing, but males at nests receiving extra food showed reduced rates of foraging. Egg production boosted the daily energy expenditure of female Ospreys by only about 20% and females gained little weight during courtship, suggesting that egg-laying is not a demanding process in this species. Because age and mate retention had a greater effect on the reproductive output and timing of female Ospreys than rates of food consumption during courtship, and because there was evidence that poorly fed females were less willing to copulate and less faithful to their mates than well-fed females, it is argued that Osprey courtship feeding may function primarily to ensure mate fidelity.