Nest-Site Selection in Relation to Habitat Edge: Experiments in the Common Goldeneye

Abstract

Habitat edges affect several ecological phenomena, usually known as the edge-effect concept. One of its basic principles is the ecological trap hypothesis which assumes that birds are attracted to nest near habitat edges where food supplies may be greater but nest predation is higher. We studied nest-site selection in relation to the lake shore/forest habitat edge in the Common Goldeneye Bucephala clangula, a hole-nesting duck, using two types of experiment. First, we examined nest-site prospecting by erecting nest boxes with traps at the shoreline and inside the forest at varying distances from the shoreline. Secondly, we examined nest-site selection in three study areas by erecting nest boxes in pairs: at the shoreline and at varying distances inside the forest. In addition we experimentally measured nest predation rate in shore and forest boxes using artificial nests. Goldeneye females prospected shore and forest boxes equally. However, the final decision was in favour of shore boxes: within a box pair, the shore box was occupied first in all three study areas. There was no difference in nest predation rate between shore and forest boxes, except in one study area where predation rate was lower, not higher, in shore boxes. Thus, while Goldeneye females clearly exhibit a pattern of nest-site selection in relation to habitat edge, the ecological trap hypothesis is not supported so far as the risk of predation is considered. Increased predation risk associated with the period of getting hatched young out of the nest to a brood-rearing lake may be the reason for the rejection of forest boxes.