Predation Risk Influences the Use of Foraging Sites by Tits

E-ISSN： 1939-9170|74|4|1197-1203

ISSN： 0012-9658

Source： Ecology, Vol.74, Iss.4, 1993-06, pp. : 1197-1203

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Abstract

In coniferous forests of Central Finland, tits (Paridae) and the Goldcrest (Regulus regulus) exploit nonrenewable resources in their group territories during the winter. Results of many studies have indicated that interspecific competition restricts the use of foraging sites in mixed—species winter flocks. However predation is a significant mortality factor in these species, and predation risk might also restrict the selection of foraging sites. The Pygmy Owl (Glaucidium passerinum) is the main diurnal predator of these small passerines during winter. Predation risk from the Pygmy Owl varies greatly with the availability of voles as alternative prey. The purpose of this study is to examine the effects of predation risk on the use of foraging sites in coniferous forest tits during winter. I collected foraging data from Willow (Parus montanus) and Crested Tits (P. cristatus) during one winter when vole populations had crashed and another winter when vole density was high to see if predation risk affects the selection of foraging sites by these species. Both Willow and Crested Tits changed to foraging in the inner parts of coniferous trees after the vole populations had crashed and when the Pygmy Owls started to hunt the tits. Additionally, in both pine and birch Willow Tits moved towards the treetops under high predation risk. Since all the foraging shifts were towards sites that are regarded to be safest from predation risk, it seems that predation risk in addition to interspecific competition influences the use of foraging sites by tits in coniferous forest.