Effects of Conifers on Aspen-breeding Bird Communities in the Sierra Nevada

We examined bird-habitat relationships within and across a range of aspen habitats in four major watersheds in the eastern Sierra Nevada mountains of California and Nevada to identify habitat features of importance to aspen-breeding birds. Using point counts and vegetation assessments from 462 individual stations between 2001 and 2003 allowed us to investigate important habitat features at watershed and regional scales. Several trends were found: bird species richness and abundance were positively correlated with lower percent conifer cover, increased herbaceous cover, and lower shrub-class aspen cover. Dusky Flycatcher (Empidonax oberholseri) presence and abundance were positively correlated with increased percent shrub-class aspen cover and lower percent tree-class cover of all conifers or individual coniferous species. Warbling Vireo (Vireo gilvus) presence and abundance were positively correlated with increased percent tree-class aspen cover. The results suggest that mature aspen stands with healthy herbaceous communities and limited or no conifer intrusion are optimal habitats for aspen-breeding birds in the eastern Sierra Nevada. To maximize bird species richness and bird abundance, management actions in aspen stands should concentrate on conifer removal, where conditions warrant, and the promotion of a healthy herbaceous layer. Conservation planning for birds in aspen habitats of the Sierra Nevada is discussed.