Breeding range translates into staging site choice: Baltic and arctic Barnacle Geese Branta leucopsis use different habitats at a Dutch Wadden Sea island

Habitat use of two populations of Barnacle Goose Branta leucopsis, one arct ic and one temperate breeding, was studied on Schiermonnikoog, an island in the Dutch Wadden Sea, during winter and spring 1988/89. Although both popu lations have overlapping winter ranges, habitat choice on a smaller scale d iffered in late winter and spring. Birds from the large arctic population m ainly used feeding grounds situated on an ungrazed natural saltmarsh, espec ially during spring, whereas birds belonging to the recently established te mperate Baltic population continued to use cattle-grazed, heavily fertilise d pastures and adjacent semi-natural cattle-grazed saltmarsh vegetation thr oughout the staging period. Barnacle Goose grazing pressure on the fertilis ed grasslands increased dramatically during the last two decades, but only little on the saltmarsh. Vegetation on improved pastures was of higher qual ity, measured in terms of nitrogen content, than vegetation on the ungrazed natural saltmarsh. Surprisingly, there was only a weak tendency that birds utilising grasslands produced more offspring. Differential energetic and n utritional needs of the two populations or an inability of arctic birds to break with their traditionally established feeding routines are the most li kely explanations for the observed pattern.