Nest-Site Selection by Marsh Harrier (Circus Aeruginosus) in the Shore Belt of Helophytes on Large Lakes

Abstract

Nest-site selection by Marsh Harrier (Circus aeruginosus) was investigated on Lakes Meteliai and Obelija in 1983–1986 and Lake Žaltytis in 1984–1986 in southern Lithuania. Fifty five breeding pairs were detected and 49 nests (89.1%) were found. With regard to the potential breeding habitat, Lakes Meteliai and Žaltytis represented extreme structural types, whereas Lake Obelija – the intermediate type. Despite these differences, most nest-site parameters of the three lakes did not differ or differed slightly. The most similar was the depth. Only the most dissimilar lakes differed according to nest-site vegetation density and height, the latter varied according to the dominant helophytic species on the lake. Distances from nests to water and shore were not statistically significant – nests were built in the middle of the emergent vegetation belt. While selecting nest-sites, pairs gave preference to patches larger in area and diameter. Nest-site selection peculiarities are explained by birds’ balanced efforts to protect clutches from terrestrial mammalian predation and the destructive impact of hydrodynamic processes.

Keywords:

• Marsh Harrier
• nest-site selection
• shore belt
• helophytes
• patch
• terrestrial predators
• hydrodynamic processes