GPS-tracking reveals winter short-stopping and large differences in individual migratory distance among Greylag Geese (Anser anser) breeding in Denmark

The exponential increase in the ‘NW/SW European Greylag Goose population’ (NGGP) has created demands for more precise estimates of the national breeding populations and improved understanding of their movements to support its effective management. Increased NGGP abundance has been associated with a northeast-ward shift in wintering centre of gravity, suggesting major changes in migratory and wintering patterns. Greater numbers of wintering Greylag Geese wintering numbers in Denmark could originate from increases in the Danish breeding population showing a more sedentary habit and/or from a higher incidence of “winter short-stopping” by birds from elsewhere. Data from the first 16 Greylag Goose deployed with GPS/GSM tracking collars in 2021 and 2022 were used to test the hypothesis that birds in newly colonised Danish breeding areas were more sedentary than the long-distance migratory geese in traditional nesting areas. Contemporary migration patterns showed that some Danish breeders (including examples from newly colonized breeding areas) still migrate to their traditional wintering quarters in southern Spain, but most tagged Greylag Geese stayed in Denmark throughout the annual cycle. These data also provided the first evidence of the occurrence of winter short-stopping among individual Danish Greylag Geese, which after one winter in Spain subsequently wintered in Denmark and the Netherlands, indicating that some individuals can shift between new wintering areas every autumn. Overall, these results show that while most Danish summering Greylag Geese are now largely resident within Denmark, some move to Germany and the Netherlands and a few still undertake the traditional long migration to southern Spain, making assignment of breeding provenance to migrating birds challenging.