Greylag Geese on Tiree and Coll, Scotland: Status, Habitat Use and Movements

Abstract

Regular counts of Greylag Geese (Anser anser) on the islands of Tiree and Coll, Argyll, Scotland have taken place since 1982. In the last 20 years, there has been a ten-fold increase with numbers leveling out since 2000 at ca. 4,000 geese. Breeding productivity, measured as percentage young in August flocks and brood sizes, was comparable to Greylag Geese on other Hebridean islands. Sightings of 1,002 individuals banded since 1998 were largely restricted to the islands, although six birds were recorded in other parts of northwest Scotland where re-sighting probability was low, indicating dispersal to new areas. The large difference between annual productivity and estimated mortality rates, coupled with the leveling-off of counts, suggested that moderate numbers might be emigrating. Greylag Geese fed primarily on silage fields and improved permanent pastures throughout the winter. Goslings remained with their parents until early April, when the adults moved to relatively remote, uncultivated land to breed. During the non-breeding season, the average flock size decreased from 70 to 22 birds. Winter home ranges of breeding adults and goslings were smaller than those of non-breeding adults and geese in their second winter, suggesting that social groups within flocks were out-competed from the preferred feeding areas and, as a result, may be more likely to disperse and colonize new areas. Geese showed individual and specific preferences for restricted parts of potential feeding areas. These basic elements of flock dynamics need to be understood when selecting management options. Current management, involving wide-scale shooting and scaring, requires provision of adequate feeding refuges to prevent dispersion of the grazing conflict to other areas, both within and beyond the two islands.