Offshore breeding in the Great Crested Grebe Podiceps cristatus: two offshore areas examined in relation to an inshore area in western Finland

Abstrakti

Offshore areas in the Baltic Sea offer extreme conditions for breeding Great Crested Grebes (e .g . lack of helophytes, strong wave action, and high sea water amplitudes) . Yet nowadays Great Crested Grebes nest fairly commonly in offshore archipelagoes in both Finland and Sweden. In this study several breeding parameters were compared in Great Crested Grebes nesting in a rocky and in a boulder-rich moraine archipelago in western Finland. The breeding of offshore grebes is on average successful (1 .55-1.60 young per pair and year) due to such factors as protection from larid colonies, good availability of food andopportunistic modifications of thebreeding . However, the egg-laying seems to be clearly later than in a traditional habitat, and the habitat and nest site selection differs between the areas studied . Areas with irregular shores may offer grebes protected microhabitats, which promotes the exploitation of even very barren archipelagoes.