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The responses of two cavity-nesting species to changes in habitat conditions and nest web community dynamics in interior British Columbia Norris, Andrea Rose


Populations of small-bodied cavity nesters may be regulated by density dependence, interspecific interactions within the community and resource availability. My objectives were to determine how changes in community interactions and habitat conditions affected mountain chickadees and red-breasted nuthatches at the local, regional and nest-patch scales. I used point count surveys and vegetation surveys from 27 forest stands to examine how population densities of mountain chickadees and red-breasted nuthatches varied with: densities of black-capped chickadees, downy woodpeckers, red-naped sapsuckers and red squirrels; densities of aspen, beetle-infected lodgepole pine trees, and all trees; and proportion of edge habitat (naturally fragmented or harvested), at the stand and study area levels from 1997-2006. For mountain chickadees, populations increased following years of high densities of nuthatches and sapsuckers and low densities of squirrels (predators) but were strongly density dependent where densities of sapsuckers and squirrels were high, and at forest edges. For red-breasted nuthatches, populations increased with recent beetle-infected pine tree density and following years of high densities of downy woodpeckers, and decreased after low densities of downy woodpeckers and high densities of black-capped chickadees. I used vegetation surveys of 231 nests and available habitat to examine nuthatch nest-patch selection. As the beetle outbreak progressed, nuthatches selected nest-patches with significantly fewer suitable nest trees and significantly more beetle-infected pine trees. The impacts of a large-scale natural disturbance event had cascading effects on the community and subsequent cavity-nester populations. Thus beetle-management activities should include long-term monitoring programs to examine temporal variability in resources and the effects on community dynamics in order to manage for chickadee and nuthatch populations.

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