ECOLOGY OF THE SLATY-BACKED GULL (LARUS SCHISTISAGUS) BREEDING ON LAKE KRONOTSKOE, KAMCHATKA PENINSULA

摘要

The slaty-backed gull population of Lake Kronotskoe has not been subjected to anthropogenic impacts for many decades. The number and distribution of the breeding colonies of slaty-backed gulls on the islands of this largest fresh-water reservoir of Kamchatka Peninsula are presented. Data on the breeding phenology, the seasonal dynamics of the food composition of breeding gulls, the foraging distance and the breeding success are considered. These data are compared to the results obtained earlier for Lake Kurilskoe. Both gull populations are unique in that they are the only fresh-water colonies within the distribution range of this marine species. The breeding success of slaty-backed gulls on Lake Kronotskoe suffers from predation, both intra-and interspecific, in the latter case from brown bears and sea eagles. The hatching period and the chicks fledging time in this population are both shifted to the end of summer, when gulls have the most abundant food available within the lake area, this increasing a successful survival of the fledglings. Despite considerable differences between the ecosystems of Lake Kronotskoe and Lake Kuril'skoe, there are several features shared in the diet of the gull populations living on the lakes. 1. Despite gulls performing 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 chick-growth period, gulls from both lakes rely on salmonids (anadromous in Lake Kuril'skoe, resident in Lake Kronotskoe) they hunt in the lakes near their colonies.