Territory and nest-site selection of Cerulean Warblers in eastern Ontario

We examined habitat selection by breeding Cerulean Warblers (Dendroica ceru lea) at three spatial scales in eastern Ontario over three years (1997-1999 ). Territories were characterized by well-spaced large trees, with high can opies and dense foliage cover at heights between 12-18 m. Nesting habitat a dditionally was characterized by dense foliage cover above 18 m. The result s of our nest-patch (0.04 ha circle around nest) and nest-site (0.01 ha cir cle) 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 selection analyses that territories likely contain mult iple nest patches and sites and that male Cerulean Warblers may defend area s with multiple nest patches or sites, which may attract females to settle with them. Whether or not Cerulean Warbler females use nest-site availabili ty as a mate- or territory-choice cue remains unknown. We also tested the v alidity of a commonly made assumption that a random sampling of habitat by researchers is representative of the habitat actually available to birds an d found that, in our study area, the assumption was invalid. Taken together , our results point toward the need to maintain sizeable stands of mature, deciduous forest to ensure the persistence of Cerulean Warblers in eastern Ontario, Population characteristics such as lower minimum area requirements and a resilience to habitat disturbance may make that an easier job in eas tern Ontario than elsewhere in this species' breeding range.