Breeding habitat characteristics of Canada Warblers in central Alberta

Determining habitat attributes used by animals of conservation concern at different spatial scales is a key aspect of developing effective recovery plans. Managers must know whether forest songbirds choose habitat based on selection of specific plant species or on structural features shared by different plant species. Coarse-scale habitat features were measured at point count locations and fine-scale characteristics within and adjacent to breeding territories of Canada Warblers (Cardellina canadensis L.) in central Alberta, Canada. Differences in the plant community composition in breeding territories between forest interior and shoreline sites were examined. Breeding success in each breeding territory was estimated through observations of males carrying food. At coarse-scales, Canada Warbler occurrence was positively correlated with shrub density and was higher in deciduous forests. At a fine-scale, woody plant species composition differed significantly between interior and shoreline sites (pseudo-F=32.61, P=0.001), but did not differ between plots located inside and outside bird territories (pseudo-F=1.22, P=0.26). Choke cherry (Prunus virginiana) was an indicator species within bird territories, however. Birds with evidence of breeding success had significantly more green alder (Alnus crispa) and balsam fir (Abies balsamea) in their territories, whereas territories without evidence of breeding success were more likely to have trembling aspen (Populus tremuloides), twining honeysuckle (Lonicera dioica) and Canada buffaloberry (Shepherdia canadensis). The results highlight that Canada Warbler presence is strongly correlated with canopy type and shrub density. There was also evidence that certain shrub and tree species are more abundant at the core of bird territories. These results will help inform critical habitat identification for Canada Warblers in western Canada. Land managers should use forest inventory data sources that include information on shrub density when trying to locate important habitat for Canada Warblers, while being aware that locally, specific plant species may influence Canada Warbler habitat choices and breeding success.