Abstract
A survey of museum specimens revealed large interspecific variability in the sex ratio in 14 species [Mew, ring-billed, laughing, Franklin's, Bonaparte's, Heerman's, California, herring, Thayer's, western, glaucous, glaucous-winged, and great black-backed gulls, and blacklegged kittiwake] of North American gulls. In the three black-headed species, (Larus atricilla, L. pipixcan, and L. philadelphia), females outnumbered males among prefledglings, but males outnumbered females among adults. In the white-headed gulls, the male/female ratio in prefledglings did not vary significantly from 1.0 in any species. However, among first-year birds, females outnumbered males in 8 white-headed species. Among adults, the male/female ratio was 1.0 in the Great Black-backed Gull, and = 1.0 in the other white-headed gulls.
Highlights
Unusual intraspecific variability in mating systems has recently been observed in some North American gulls
These species are predominantly monogamous, polygyny has recently been observed in Herring Gulls (Lams argentatus) (Shugart and Southern 1977, Fitch 1980, Shugart 1981) and Ring-billed Gulls (L. delawarensis) (Conover et al 1979, Conover 1984)
Female-female pairings have been discovered in Herring Gulls (Fitch 1980, Shugart 1981); Ring-billed Gulls (Ryder and Somppi 1979, Conover et al 1979, Conover 1984); Californa Gulls (L. californicus) (Conover et al 1979, Conover 1984) and Western Gulls (L. occidentalis) (Hunt and Hunt 1977)
Summary
' Depanment of Plant Pathology and Ecology, The Connecticut Agricultural Experiment Si.ation, Box I 106, New Haven, Connecticut 06504 USA; and. Burger and Gochfeld (1981) presented some data indicating that female Herring Gulls may outnumber males in breeding colonies in Maine and New York, two areas where female-female pairings have not been detected. An evaluation of these hypotheses or other theories concerning avian sex ratios is hampered by a paucity of data on the sex ratios in gu ll populations and other avian groups. We tested whether intraspecific sex ratios varied among age classes, collection locations, and collection seasons
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