AN EXPERIMENT ON NEST-SITE CHOICE OF THE COMMON TREECREEPER IN FRAGMENTED BOREAL FOREST

Experiments in the nest site choice of breeding birds in relation to t he distance from habitat edge are missing or few. We performed such an experiment with the aid of nest-box -breeding Common Treecreepers Cer thia familiaris. In their first choice of the breeding site, Treecreep ers clearly favoured the boxes further away from the forest edge. In c onsequence, the number of successful breeding attempts was higher for the nests further away from the edge. There are two possible hypothese s to explain the results. First, the central place foraging theory pre dicts that a circular foraging range is optimal. The home range size o f a breeding treecreeper pair is, on average, 3.3 ha, therefore, the n est of this species should be located at least 102 m from the forest e dge in order to maintain a 3.3 ha circular foraging area. The results agree with this expectation, because in the first choice of nesting si tes 65 per cent of the nests were further than 100 m from the edge. Se condly, nest predation often considerably reduces the breeding success of small passerine birds nesting nearby the forest edge. Treecreepers suffer high nest predation pressure, in particular when breeding in n atural nest sites. If predation pressure is higher near the edge that may also contribute to the choice of a nest site further away from the forest edge.