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Do black-throated green warblers prefer conifers? Meso- and microhabitat use in a mixedwood forest

Document Type

Article

Journal/Book Title/Conference

Condor

Volume

101

Issue

2

First Page

262

Last Page

271

Publication Date

1999

Abstract

Throughout most of its range, the Black-throated Green Warbler (Dendroica virens) is generally associated with coniferous forests, but it also breeds in mixedwood and deciduous stands. To measure the relative use of deciduous and coniferous trees in pristine boreal mixedwood stands of northern Alberta, we examined the influence of conifer distribution on territory placement at the mesohabitat scale (25-ha study plots) and substrate use for singing and foraging at the microhabitat scale (within individual territories). Black-throated Green Warblers clustered their territories where conifers reached their highest density, and tended to avoid areas where conifers were rare or absent. At the microhabitat scale, logistic regression models indicate that tree species and diameter at breast height were significant predictors of tree use; Black-throated Green Warblers mainly used large white spruce (Picea glauca) trees as songposts and foraging substrates. For foraging, trembling aspen (Populus tremuloides) and balsam poplar (P. balsamifera), the two most abundant tree species in our plots, were less frequently used than white spruce, whereas paper birch (Betula papyrifera) was used according to its availability. These results indicate that Black-throated Green Warblers were relatively stereotyped in their substrate use, in spite of the availability of both deciduous and coniferous trees. However, the treefall gaps and dense deciduous shrub layer typical of old boreal mixedwood stands might be important at the fledgling stage. Thus, the conversion of mixedwood forests into pure deciduous stands and conifer plantations could have negative impacts on this and other ecologically-similar species in the boreal forest.

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