Ardea
Official journal of the Netherlands Ornithologists' Union

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Durell S.E.A. le V. dit & Goss-Custard J.D. (1996) Oystercatcher Haematopus ostralegus sex ratios on the wintering grounds: the case of the Exe estuary. ARDEA 84 (A): 373-381
Data on bird numbers, age distribution, habitat use and feeding methods collected over 15 years were used, in conjunction with the sex ratios found within birds having particular bill tip shapes, to estimate the sex ratio of the total overwintering population of Oystercatchers on the Exe estuary, SW. England. The proportion of ## was estimated to be 36-38% in juveniles, 50-53% in immatures and 66-67% in adults. Possible explanations for the male bias amongst adult Oystercatchers on the Exe, and the change in sex ratios with age, were examined by the use of a simple population model. Disproportionate emigration of young ~~ and immigration of young ## would have to be at unrealistically high levels in order to achieve the sex ratio found amongst adults. Mortality in young ~~ would have to be 15% higher than in ## to achieve the same results. It is argued that both disproportionate emigration/immigration and higher female mortality in young birds must occur, and that there is probably higher female mortality amongst young adults.


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