Variability in Nest Density, Occupancy, and Home Range Size of Western Bluebirds after Forest Treatments
Complex land use and fuels management histories have resulted in significant changes in composition, structure, and function of southwestern forests and subsequent changes in the extent and quality of wildlife habitats. We evaluated how several currently used fuel reduction treatments (e.g., mechanical thinning and prescribed fire alone and in combination) affect nest attributes, nest density, nest tree occupancy, and home range size of Western Bluebirds (Sialia mexicana) in ponderosa pine (Pinus ponderosa)-dominated forests of northern Arizona. Nest attributes, such as number of eggs or nestlings, varied among treatments, but did not differ statistically. Western Bluebird nest density was significantly influenced by treatment, with densities higher in treated areas, even though snag density was lower in treated areas than in control areas. The average (± SE) area of the 50% contour, across all treatment units, was 0.42 ± 0.07 ha, and the average area of the 90% contour was 2.36 ± 0.30 ha. Home range sizes for both probability contours evaluated were 1.5 times larger in the thin-only treatments than in the control units. Conversely, home range area in thin-and-burn treatments was approximately 30% smaller than in control units. The largest home ranges occurred in the burn-only treatments. Our results suggest that forest treatments, such as thinning and prescribed fire are, in general, beneficial to Western Bluebirds, but that low snag retention may be problematic in areas receiving prescribed fire as part of their treatment action.
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