Sexual Differences in Parental Activities of Breeding Black Skimmers

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Abstract
Black skimmers (Rynchops niger) were studied because it is easy to distinguish the sexes, they are monogamous and they nest in colonies, making it possible to gather sufficient data on several pairs under the same environmental conditions. Skimmers forage during the day and at night so that both sexes probably spend more time on the territory during the day than if they only foraged during the day. Observations at night indicated that they did not engage in territorial interactions at night. The study indicated similar investment for males and females in time (and energy) for the production of offspring. Males spend more time in aggressive interactions during the prelaying and egg-laying (and in the re-laying) periods than do females. This may occur because males must prevent females from being inseminated by other males. Only more field work can ascertain the potential for cuckoldry. Contrary to Trivers it was suggested that males of monogamous birds must invest more, rather than less, in the reproductive effort.