Effects of predation risk on site selection of barnacle geese during brood-rearing

Barnacle geese Branta leucopsis breed on small islands in the Kongsfjorden area, Spitsbergen. Shortly after hatching, families approach feeding sites at the mainland coast in the close surroundings of the village Ny-Alesund. The goslings are subject to predation by arctic foxes Alopex lagopus throughout the whole brood-rearing period. This study compares the choice of foraging areas in a year with fox predation with years with no foxes present. Observations of ringed individuals show that the use of tundra sires by families decreases in a year with foxes present. In such a year, foraging of goose families is limited to sites in the proximity of open water. Non-breeders are not affected in their choice of foraging areas by the presence of arctic foxes and prefer sites along lake shores during wing moult. Habitats vary in food quality and quantity according to the dominant vegetation type. Approximately 85% of the diet of geese grazing on meadows within the village and on tundra sites consists of graminoids and dicots, whereas geese grazing on lake shores consume up to 35% moss. A grass-dominated diet yields good digestibility and a favourable protein gain, compared to moss which is of lower quality. In a fox year, predation risk restricts goose families to a small range of safe foraging sites where grazing pressure is high. Data on slower gosling growth support the hypothesis of food limitation and competition among families in such a year