TERRITORY AND NEST-SITE SELECTION OF CERULEAN WARBLERS IN EASTERN ONTARIO

Abstract

ABSTRACT.—We examined habitat selection by breeding CeruleanWarblers (Dendroica cer- ulea) at three spatial scales in eastern Ontario over three years (1997–1999). Territories were characterized by well-spaced large trees, with high canopies and dense foliage cover at heights between 12–18 m. Nesting habitat additionally was characterized by dense foliage cover above 18 m. The results of our nest-patch (0.04 ha circle around nest) and nest-site (0.01 ha circle) analyses indicate that male Cerulean Warblers may take active roles in nest- site selection when selecting territories. We conclude from our nest-patch and nest-site se- lection analyses that territories likely contain multiple nest patches and sites and that male Cerulean Warblers may defend areas with multiple nest patches or sites, which may attract females to settle with them. Whether or not Cerulean Warbler females use nest-site avail- ability as a mate- or territory-choice cue remains unknown. We also tested the validity of a commonly made assumption that a random sampling of habitat by researchers is represen- tative of the habitat actually available to birds and found that, in our study area, the as- sumptionwas invalid. Taken together, our results point toward the need to maintain sizeable stands of mature, deciduous forest to ensure the persistence of CeruleanWarblers in eastern Ontario. Population characteristics such as lower minimum area requirements and a resil- ience to habitat disturbance may make that an easier job in eastern Ontario than elsewhere in this species’ breeding range.