Niche Relationships and Life-History Tactics of Three Sympatric Strix Owl Species in Finland

Abstract

Niche relationships of three sympatric Strix owl species in Finland were studied with respect to four environmental parameters: activity, food, breeding habitat and nestsite. The niches of Ural and Tawny Owls have the highest mutual overlap indicating possible interspecific competition, which may cause the patchy occurrence of the Tawny Owl in southern Finland. The Ural Owl has the widest niche, that of Tawny Owl is 73% and that of Great Grey Owl only 48% of the niche of the first-mentioned species. The Great Grey Owl is a r-strategist, which has adapted to the vole cycles in the northern taiga zone by being nomadic, opportunistically selecting its breeding habitats, using commonly available nest-sites, being a vole specialist, laying large clutches and being active during day and night. The Tawny Owl again is adapted to the more stable, southern environment, since it breeds in productive habitats, is a food generalist, as a resident species defends its nest-hole, is nocturnal and a K-strategist. Considering distribution, breeding habitat and daily activity, the Ural Owl is intermediate, but because of its large size it is capable of being a food generalist, resident and a K-strategist. Thus, the life-history traits of the three owl species agree relatively well with the correlates of r-and K-selection, apart from the large size of the Great Grey Owl. This may be an adaptation to the capturing of voles below the deep snow and to the hard wintering and breeding conditions.