Anjolene R. Hunt & Erin M. Bayne (Department of Biological Sciences, University of Alberta) and Samuel Haché (Environment and Climate Change Canada)
2017
Abstract
The Canada Warbler (Cardellina canadensis) is a threatened species in Canada due to an annual decline of ~3% annually over the last 50 years. Forestry is potentially a cause of these declines as some studies suggest Canada Warblers prefer old-growth forest. However, some studies suggest Canada Warblers will use harvested areas. Differences in scale between habitat use studies and behavioural phenomena such as conspecific attraction may explain these discrepancies. We quantified multiple orders of habitat use and how this influenced reproductive success to study the response of the Canada Warbler to forestry in Alberta while accounting for conspecific attraction. Point count surveys and tracked individuals where used to understand how density, 2nd and 3rd order habitat use, and probability of pairing and fledging young for male Canada Warblers were influenced by amount, type and age of forest harvest. Forest harvesting had negative effects on density and 2nd order use. Local vegetation structure, forest age within post-harvest stands, or retention of unharvested fragments did not influence use of harvested areas. However, males were more likely to use post-harvest stands in areas close to adjacent unharvested stands and areas near conspecifics (2nd order). Within the home range, intensity of use (3rd order) was highest in unharvested stands, closer to conspecifics, and further from post- harvest-unharvested edges. Lastly, there was no evidence that forestry affected pairing or probability of fledging young, but pairing success was lower in areas with a higher density of Canada Warblers. Our results suggest use of post-harvest stands by Canada Warblers on their boreal breeding grounds is influenced more by conspecifics than by attributes of post-harvest stands themselves. Conservation efforts should prioritize the retention of large tracts of unharvested forest near occupied breeding sites to support high densities of Canada Warblers resulting from the species’ clustered breeding distribution.
DOI: 10.1650/CONDOR-17-35.1
# 16-ERPC-08C