DOES THE DOMINANT NUTHATCH SITTA-EUROPAEA AFFECT THE FORAGING BEHAVIOR OF THE SUBORDINATE TREECREEPER CERTHIA-BRACHYDACTYLA IN SMALL FORESTFRAGMENTS

We studied the winter foraging behaviour of Short-toed Treecreeper Cer thia brachydactyla and Nuthatch Sitta europaea in 18 deciduous forest fragments varying in size between 1 and 30 ha and in one forest of abo ut 200 ha in order to examine how forest area and the presence/absence of the dominant Nuthatch affect the foraging behaviour of the subordi nate Treecreeper. The Treecreeper occurred in 14 out of 18 forest frag ments while the Nuthatch was only observed in seven, mainly in fragmen ts exceeding 4 ha. We found no effect of forest size on any of the com ponents of the foraging niches of either Treecreeper or Nuthatch, and Treecreeper foraging niches did not become broader in the smaller frag ments in which Nuthatches were absent. The significant niche change we did observe was opposite to the expected direction. We conclude that winter foraging niches of small insectivorous birds do not necessarily expand in the absence of close competitors in island-like situations.