Geographic origin of migratory birds based on stable isotope analysis: the case of the greylag goose (Anser anser) wintering in Camargue, southern France

Abstract

Proper delineation of flyways is a prerequisite for adequate management of migratory birds. The implementation of coordinated international management for greylag goose (Anser anser) is currently underway in Europe for the north-west/south-west (NW/SW) population. Some uncertainty remained as to whether greylags wintering in Camargue, Southern France, belonged to this population and bred in Norway, Sweden and Finland, or rather originated from the Central European population, especially since most neck collar observations were of birds ringed in the Czech Republic. Stable hydrogen isotope (δ2H) analyses of feathers from 147 individuals hunted or trapped during winter in Camargue provide some insight into this question and suggest north-central Europe as a more likely area of origin. This indicates that greylags wintering along the Mediterranean coast may be largely separate from the birds of the NW/SW European population breeding in Fennoscandia, although some individuals may also come from the Polish or German regions of the NW/SW flyway, since the combined ringing and stable isotope analyses suggest these birds are mostly breeding and moulting in an isotopic area consistent with the Czech Republic, Poland and northern Germany. Earlier studies show birds wintering in other French regions rather originate from Sweden and Norway. These results should be considered for the management plan currently being developed for greylag goose in Europe. More generally, they question whether birds from two distinct populations/flyways should be applied similar or potentially different management plans within a given country.