Bird responses to removal of western juniper in sagebrush-steppe

Abstract

We investigated bird abundance in response to western juniper (Juniperus occidentalis) removal using a short-term chronosequence approach and generated estimates of density and responses to management for the most abundant species. Stands targeted for tree removal were primarily in the middle stages of juniper encroachment (Phase II, 7 851 ha). Trees were removed using hand felling combined with either lop and scatter, single tree burning, or jackpot burning, which were carried out to minimize loss of shrub cover. Brewer's sparrow (Spizella breweri) density was greater at treated versus untreated portions of the study area. At sites in the third year following tree removal, Brewer's sparrow density was 23.6 (95% confidence interval [CI]: 19.4-27.8) territories per km2 higher than locations that had not yet been treated. This equates to a net increase of 1 212-1 737 nesting pairs within the project area. Green-tailed towhee increased by 4.6 (95% CI: 3.1-6.1) territories per km2 for an estimated project wide increase of 194-381 nesting pairs, and vesper sparrow (Poocetes gramineus) increased by 6.5 (95% CI: 4.6-8.4) territories per km2 corresponding to an estimated increase of 460-559 nesting pairs within the project area. Density of gray flycatcher (Empidonax wrighti) was lower in cut areas, and over the entire project area we estimate a net loss of 183-486 nesting pairs as a result of juniper tree removal. This study demonstrates that conifer removal projects designed to retain shrub cover and structure can have benefits to multiple species of ground and shrub nesting birds, including several species of conservation concern.