Demographic monitoring is vital for tracking and modelling the population dynamics of highly mobile bird populations. However, different types of monitoring can sometimes lead to different outcomes, and understanding the causes of equivocal results is an important step to advance future monitoring schemes. This study found consistent seasonal variation in Eurasian Wigeon Anas penelope sex and age ratios among Danish hunter-based wing surveys, and describes how accounting for this variation might explain reported discrepancies between this and other monitoring methods. Early season flocks were dominated by adult males, and juvenile proportions were highest in November and significantly lower before and after this peak. Nationwide field assessments undertaken in January 2012 showed no significant differences from sex and age ratios in the wing survey data from that particular hunting season (2011/2012), indicating that this survey is a good predictor of Wigeon demography. These results highlight the need to account for consistent temporal variation in such demographic time series when using the results to model population parameters.
Journal of Ornithology, 2013, Vol 154, Issue 3, p. 769-774