Autumn survival inferred from wing age ratios: wigeon juvenile survival half that of adults at best?

Measures of first-year autumn mortality rates are important parameters for understanding population dynamics, but have been hitherto unavailable for dabbling ducks in Europe, because most ducks are ringed in winter. We used the temporal change in the proportion of juveniles in wing samples from hunters in Finland, Denmark and UK, together with adult survival estimates from the literature, to estimate juvenile autumn survival in Wigeon Anas Penelope. Wing samples from Finland and Denmark were collected during the late breeding (August–September) and migration (October–December) periods. The proportion of juveniles decreased from 80 % (females) and 74 % (males) in Finland to 63 and 45 % in Denmark, respectively. Combining the changes in the proportion of juveniles in the wing sample with adult Wigeon 3-month survival rates inferred from a Bayesian meta-analysis (89 % in males and 88 % in females), estimated autumn juvenile survival probability was 29 % for females and 22 % for males. The results show that autumn mortality is far higher in juvenile Wigeon than amongst adults, consistent with previous results in Teal Anas crecca, and may reflect a wider pattern in dabbling ducks. Such low survival rates are especially important in Wigeon given observed long-term declines in breeding productivity in this population.

Keywords: Wing examination, Hunting bag, Age ratio, Survival, Autumn