Between-year variations in sex/age ratio bias in hunter wings of Eurasian Wigeon (Anas penelope) compared to field samples

Abstract

We compared age and sex ratios amongst Eurasian Wigeon (Anas penelope) derived from Danish field observations and hunter-based shot samples throughout an entire winter in two consecutive years. In the middle period of both winters, sex ratios did not differ significantly between the two samples. However, first-year males were more than three times more likely to be represented than adult males in the hunter sample compared to field samples and were 4–22 times overrepresented in the hunting sample at the beginning of both seasons. We found between and within-season differences in bias, confirming the need to account for such bias and its temporal variation when using the results of wing surveys to model population parameters. However, given the relative uniformity in bias in the middle part of both seasons, these results confirm that age ratios amongst wings voluntarily contributed by hunters provide an invaluable long term measure of reproductive success in dabbling duck populations as long as we can account for such bias.