VEGETATION EXPLOITATION BY BARNACLE GEESE BRANTA-LEUCOPSIS DURING INCUBATION ON SVALBARD

The paper is a study of vegetation exploitation and the effect of food availability on the diet and behaviour in barnacle geese breeding at Storholmen, Svalbard. Detailed vegetation mapping was used to estimate the availability of food to individual pairs of geese. Diet compositi on was assessed through analysis of plant fragments in droppings. The behaviour of geese in relation to snowmelt patterns was recorded. Most vegetation types were exploited by the geese either for feeding or as nest substrate, Nest density was highest and territories were smalles t on early, snow-free ridges, although late breeding individuals also nested in moss tundra vegetation. Most geese pairs exploited a mosaic of vegetation types in their territories, which extended the feeding p eriod when plants were nutritionally most profitable to the geese. Ter ritory size increased with decreasing density of the highest preferred food plants. Female geese preferred plants with high nutrient quality , and the diet during incubation consisted of 41% flowers of forbs, 19 % grasses, 6% leaves and buds of forbs, and 34% mosses. When the avail ability of grasses was <5%, geese switched to a diet dominated by the abundant, but nutrient-poor, mosses, The nutrient-poor diet resulted i n more time off the nest and less time being alert or searching for fo od during feeding bouts. Because nests are exposed to predators when f emales feed or search for food, a low availability of nutrient-rich fo od within the territory can affect hatching success.