Multi-annual spatial and numeric dynamics of the white-headed duck Oxyura leucocephala in southern Europe: seasonality, density dependence and climatic variability

1. A statistical model is developed for the globally threatened white-headed duck during its regional expansion throughout Spain from 1980 to 2000; the model estimates the relative intrinsic, climatic and stochastic effects on population fluctuations and spatial expansion on several time-scales. Facing the current lack of knowledge on the nature and consequences of regulation for waterfowl populations, this type of study seems timely. 2. A measure of population density accounting for the spatial patchiness of the population was constructed for breeding and wintering counts. No relationship was found between spatial and numeric dynamics, which suggests different mechanisms for both dynamical patterns. 3. Although a lagged non-linear climatic effect during the period of chick rearing enhanced numeric brood recruitment through a cohort effect, in the short term brood production appeared to decrease with increasing population density, despite a longterm exponential numeric growth. 4. Both wintering population density and rainfall during post-nuptial moult exerted a positive effect on subsequent spatial expansion during breeding, which suggest a major role for social interactions during wintering and wetlands availability on spatial dynamics. 5. Altogether, the results suggest that seasonality, density-dependence and climatic forcing are all major processes in the spatio-temporal dynamics of the white-headed duck. Ignoring the relative biotic and abiotic effects and their temporal scale of interaction on population dynamics might thus yield misleading conclusions on the factors affecting the shortand long-term abundance of waterfowl populations.