Nest Site Selection of Two Sympatric Tern Species (Ayes: Laridae) in South-western Siberia

Habitat loss and impoverishment arc the main factors causing the decline in populations of water bird species. To acquire the knowledge necessary for their conservation, an understanding of how they use their breeding habitats is crucial. With this in mind, the sympatric tern species White-winged Tern Chlidonias leucopterus and Black Tern Chlidonias niger were studied in the Kulunda steppe of Altai Krai in southern Russia. Although both species occurred in the same area, they differed in their use of nesting habitats. Black Tern located its colonies mostly in emergent vegetation, whereas White-winged Tern did so more often in patches of sedge. In order to define nest site selectivity, models containing seven habitat predictors were developed on the basis of Akaike's information criterion. The best model for Black Tern showed that it chose a larger area of water bodies close to the colonies than around unoccupied sites. For White-winged Tern, the distances from the colony to the nearest woodland and to the nearest settlements were greater. These habitat factors may be primarily related to the different feeding preferences of the two species and in the case of White-winged Tern may be connected with the risk of nest loss.