Seasonal differences in courtship feeding rates of male common terns

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Abstract
Courtship feeding rates by male common terns (Sterna hirundo) nesting late in the 1982 breeding season were markedly lower than those of peak nesters in that year. In 1983, however, there were no differences in courtship feeding rates between peak and late nesters. Both groups of males in 1983 fed females at similar rates before the first eggs were laid, and both rates declined after the second eggs were laid. Larger fish were fed to the females later in the season. Late nesting males adjusted their feeding rates to the size of fish delivered; males feeding larger fish fed them at a lower rate than males feeding smaller fish. There was no difference in the weights of three-egg clutches laid by peak and late nesting females, and there was no correlation between courtship feeding rate and clutch weight. As all females were apparently able to obtain sufficient nutrition to provision their eggs adequately, I suggest that 1983 was an unusually favourable food year at Port Colborne. This view accepts courtship feeding as an adaptation enabling the female to obtain sufficient nutrients before and during egg laying. Other functions of the behaviour at other times during a breeding bout are not precluded.