Sex ratios of waders at the northern end of the East Atlantic flyway in winter

摘要

Capsule Sex ratios were determined for 11 wader species at the northern end of the East Atlantic flyway in winter. The ratio was even for six species, there were more males for four species, and more females for one species.Aims To describe the sex ratio of adult waders in northern Scotland and examine departures from parity.Methods Molecular sexing and biometrics were used to estimate the sex ratio (percentage male) in adult populations of 11 waders wintering on estuaries and open shores in northern Scotland (Moray Firth and Orkney), at the northern part of the East Atlantic flyway. Departures from parity were examined in relation to three possibilities: (1) that there was local variation in the distribution of the sexes; (2) that the sexes differed in their winter ranges and (3) that there was an uneven sex ratio in the entire population.Results The percentage of males did not differ significantly from 50% for Lapwing, Ringed Plover, Dunlin, Knot, Sanderling and Turnstone. There were significant differences from parity for Oystercatcher, Redshank, Bar-tailed Godwit and Curlew at some sites, suggesting local segregation of the sexes that may be related to habitat. It was difficult to examine possibilities 2 and 3 due to the lack of data from other parts of the flyway. Only some populations of Purple Sandpipers and perhaps Bar-tailed Godwits exhibited an uneven sex ratio in favour of males across the flyway. For these species, the uneven sex ratio in favour of males was already apparent in first-year birds, showing that higher mortality amongst juvenile females, rather than higher mortality amongst breeding females probably causes the imbalance.Conclusion Some waders showed significant deviations from parity in their sex ratio. These may be due to sex-dependent habitat selection and differential mortality rates.