Ringing, tracking and counting data reveal five wintering patterns in European Common Shelducks

Information on migratory connections provides a basis for effective conservation efforts. The spatial connections between breeding and wintering areas are poorly known for many species. The connections become complicated in species that carry out additional migrations between their breeding and wintering areas. Common Shelducks Tadorna tadorna (hereafter Shelducks) in western Europe perform an extensive moult migration after the breeding season. In this study, we examined the geographical connections between the breeding and wintering areas to identify ecological patterns, and estimate the influence of moult migration. Possible patterns would be to winter: (I) in distant and separate areas; (II) in a moulting area; (III) in the vicinity of a moulting area; (IV) near the individual breeding area. Further, there might be individuals (V) that breed, moult and winter in the same area (sedentary). We analysed recoveries of ringed Shelducks from the EURING databank and count data from the International Waterbird Census, and tracked 11 individuals from a German breeding population using GPS transmitters. We found evidence of all possible wintering patterns in Shelducks breeding in regions of Europe with long-term mean January temperatures at least slightly above 0 °C. Shelducks from cold parts of Europe always migrated to separate and warmer wintering areas. Shelducks from warmer regions used diverse patterns even within the same breeding populations. Some individuals used wintering areas near or in a moulting area, even if that area was sometimes colder than their breeding area. Our results support the idea that the location of the moulting area influenced the geographical position of the wintering area. Furthermore, the observed low migratory connectivity and high diversity in wintering patterns support the idea that Common Shelducks are able to adapt to changing environmental conditions.