THE IMPORTANCE OF BODY RESERVES ACCUMULATED IN SPRING STAGING AREAS IN THE TEMPERATE ZONE FOR BREEDING IN DARK-BELLIED BRENT GEESE BRANTA-B-BERNICLA IN THE HIGH ARCTIC

Seasonal changes in body mass of Arctic-nesting Brent Geese are charac terized by a depression in early April, followed by a sharp increase d uring pre-migratory fattening. Both male and female Brent Geese increa sed their body mass by 25-35% in the Wadden Sea in April/May. Paired f emales reach on average higher body masses than single females. Female Brent Geese that returned with offspring to the wintering quarters in western Europe had on average been heavier at spring departure from t he staging grounds in the Wadden Sea, than those failing to raise offs pring. This difference remained significant after correcting for body size (i.e. wing length). In males, corrected spring body mass had no e ffect on subsequent breeding success. Measurements of changes in body mass of incubating female Brent Geese, coupled to estimated flying cos ts (based on data on body mass, wing span and total wing area) showed that body reserves stored in the Wadden Sea were insufficient to accom plish both migration and successful breeding. Presumably the geese ref uelled in the White Sea, in order to complete their spring migration a nd arrive on the breeding grounds in Taymyr in the condition necessary for successful breeding.