Short-term effects of fire and fire surrogate treatments on foraging tree selection by cavity-nesting birds in dry forests of central Washington

Abstract

Dry forests of Washington are becoming increasingly susceptible to broadscale stand replacement fire and insect and disease epidemics. In response, land managers implement fuel reduction strategies. These situations could potentially affect numerous wildlife species, including cavity-nesting birds. Much information exists on nesting requirements of cavity-nesters, while little information is available on their foraging requirements, or how changes to their habitat affect foraging. We examined short-term responses of cavity-nesting birds in dry conifer forests of Washington, to fuel reduction treatments in 2004 and 2005, as part of the National Fire–Fire Surrogate Project (FFS). Our objective was to determine if altering the forest stand through mechanical thinning or prescribed burning or a combination of the two would alter foraging tree selection. We used linear logistic regression and Akaike's Information Criteria (AIC) to model foraging tree selection and to analyze the effects of treatments on foraging tree selection. Model averaged parameter estimates suggested that cavity-nesting birds selected for large diameter trees and FFS treatments had a positive impact on foraging for nuthatches and woodpeckers. Birds were more likely to be observed foraging in treated stands and the positive relationship was strongest in stands that received a combination of thinning and burning treatments. Enhanced foraging conditions in the thin–burn treatment may have resulted from a more complete removal of small trees, while the prescribed burn was so low-intensity, it did not remove many small trees. Bird groups selected for trees at least 1.6 times as large in diameter in treated stands as compared to control stands. Our results indicate activities such as thinning and burning may best enhance foraging habitat for bark gleaning species as a whole. Our data suggests that some important treatment design considerations include the removal of small trees and the retention of large trees and snags (>40 cm dbh) that provide important foraging substrate and nesting habitat.