Ecology of Slaty-Backed Gull (Larus schistisagus) Breeding on Kronotskoe Lake, Kamchatka Peninsula

Abstract

The slaty-backed gull population of Kronotskoe Lake has not been subjected to anthropogenic impact for many decades. The number and distribution of the breeding colonies of the slaty-backed gulls on the islands of this largest freshwater reservoir of the Kamchatka Peninsula are presented. Data on the breeding phenology, the seasonal dynamics of the food composition of breeding gulls, the foraging distance, and breeding success are considered. These data are compared to the results obtained earlier for Kuril’skoe Lake. Both gull populations are unique in that they are the only freshwater colonies within the distribution range of this marine species. The breeding success of the slaty-backed gulls on Kronotskoe Lake suffers from predation, both intra- and interspecific, in the latter case from brown bears and sea eagles. The hatching period and the fledging time of chicks in this population are both shifted to the end of summer, when gulls have the most abundant food available within the lake area, which increases successful survival of the fledglings. Despite considerable differences between the ecosystems of Kronotskoe Lake and Kuril’skoe Lake, there are several common features in the diets of the gull populations living on the lakes: (1) Despite the fact that gulls perform foraging flights to the sea coast, they only take fish and almost never collect marine invertebrates there. (2) Nearly half of all food items are taken within a 40-km distance from the colony. (3) During the growth period of chicks, gulls from both lakes rely on salmonids (anadromous in Kuril’skoe Lake, resident in Kronotskoe Lake) that they hunt in the lakes near their colonies.