In the present study we focused on the case of game restocking, which implies the release of millions of individuals worldwide each year [15] . Birds are the most frequently involved, with millions of individuals being released annually in Europe only. For example more than 3 millions red-legged partridges are released annually in Spain [15] , and ca. 1.4 million Mallards are being so in France [16] . The Camargue region, a complex network of wetlands situated in the Rhone delta, is a major duck winter quarter [17] and a central place for wildfowl hunting in France [18] . Hunting is also among the most important economic activities in the area, which is one of the reasons for the massive Mallard releases in the Camargue [19] . At least 30 000 hand-reared individuals are released annually in the region [20] . Maximum Mallard numbers in the wild are reached in September after the beginning of the hunting season, with 56 500 individuals on average over the last seven years (Gauthier-Clerc, unpubl. data), these numbers certainly include a mixing of wild and released Mallards. Given its central position on the flyway of many European migratory species, the Camargue is also a potential hotspot for the introduction and transmission of bird-borne pathogens [21] .