Study of the breeding ecology and behaviour of the Svalbard population of light-bellied brent goose Branta bernicla hrota

Abstract

Nesting ecology and behaviour of the Light-bellied Brent Goose was studied on Lurøya and adjacent islands in the Tusenoyane group, SE Svalbard, from 13 June to 30 July 1987. On Lurøya 38 pairs attempted to nest, and in the whole study area 98 pairs. Estimated median data of laying of first egg was 10 June, and median hatching date 7 July. Mean clutch size in the middle of the incubation period was 4.0 eggs. On Lurtfya nesting success was 25.7%, hatching success 28.6%, and hatching success for the whole study area was c. 24%. Most losses were attributed to predation (62% of all eggs), polar bears being the most severe predators. Until mid July the islands were surrounded by drift ice, and bears occurred regularly. Bears not only damaged nests but also created disturbance in the nesting colony, offering Arctic Skuas opportunity to take eggs from deserted nests. Other losses were due to female nest desertion during late incubation. Post-hatching losses were negligible. 17 pairs of Barnacle Geese nested on an island adjacent to Lurøya, and pairs were nest prospecting on Lurøya, but were effectively expelled by territorial Brent males. During nesting, territorial Brent males spent most of the time in vigilance, followed by grazing and resting. Intruding avian predators and other geese were vigorously chased out of the territories. On average females were attentive to their nests 91% of the time. The rest of the time was spent foraging and preening in the territory. During nesting, time off the nest increased. Food resources on the islands were poor. Moss constituted the staple part of the diet during nesting and post-hatching, but the geese selected Cochlearia and Saxifraga. In wet moss carpets where most foraging took place, Cochlearia was almost completely depleted. The high predation pressure observed may be the prime factor responsible for the general low reproductive output of the population, as observed in the Danish wintering quarters. It seems that the Barnacle Goose population on Tusenøyane is expanding, and interspecific competition for nest sites and food may arise.