Age demographics of a non-breeding Eurasian Woodcock Scolopax rusticola population in relation to environmental factors

ABSTRACT Capsule Environmental conditions in non-breeding areas cause differential winter distribution patterns between age classes in a Eurasian Woodcock Scolopax rusticola population wintering in northern Iberia. Aims To determine the factors driving spatial distribution of first-winter and adult birds in the non-breeding period of a population of the Eurasian Woodcock, in order to make decisions for the management of the species. Methods Using a data set of 10 consecutive winters (2009/10–2018/19), we tested for the effect of year, geographical and habitat-related variables on age ratio and body condition of Eurasian Woodcocks wintering in two nearby zones with different hunting regimes in northern Iberia. Results Our results suggest that the age ratio depended mainly on year, month, and altitude. As winters progressed, we observed a higher proportion of first-winter birds occurring at sites with lower altitude. First-winter birds were in poorer body condition than adults, and body condition was higher in mid-winter and spring. The effect of hunting on body condition was unclear. Discussion Variation in the population structure and body condition between age classes are discussed in the context of age-dependent wintering strategies, which to a large extent depend on survival thresholds that take into account foraging efficiency and the risk of predation. The lack of detectable effects of hunting on age structure and body condition precludes us from giving any management recommendations for northern Iberia.