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Measures of annual breeding success amongst Eurasian Wigeon Anas penelope


, : Measures of annual breeding success amongst Eurasian Wigeon Anas penelope. Bird Study 55(Part 1): 43-51

Capsule Inferences are drawn on the basis of first-winter young:adult ratios.Aim To obtain the most error- and bias-free index of annual reproductive success for the species based on existing data.Methods We compared age and sex ratios amongst shot birds in Denmark and the UK with those amongst samples of birds caught for ringing purposes and field observations in the UK.Results The annual proportions of young amongst the four samples were highly correlated. The ratio of adult males to adult females showed no significant difference between any of the measures, but was lowest amongst field observations. The ratio of first-winter males to first-winter females was even in the ringing and shot samples, suggesting differential survival of the sexes after the first winter affects the global sex ratio. In the ringed sample, the proportion of first-winter birds was similar from November to March, suggesting winter migrants to the UK contained a similar proportion of adults to first-winter birds. Over the same period, the proportion of first-winter birds determined by field observations increased, suggesting the timing of body moult in winter males may overestimate numbers of females in autumn flocks. Annual variation in productivity from samples of duck wings collected in Denmark and the UK were correlated, and, on average, were 9% higher in Denmark. There was a significant long-term decline in the proportion of young recorded in the UK.Conclusion There was support for the prediction that selective hunting affects age (but apparently not sex) ratios of Wigeon in winter. It was concluded that hunting bags and ringing samples could provide useful indices of annual production of young over extended periods and that production of young was correlated with temperatures on the breeding grounds.

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