Disturbance as restoration in the intermountain sagebrush-steppe: Effects on non-target bird species.

摘要

Changes in shrubsteppe passerine bird habitat associations in response to disturbance were investigated at multiple temporal and spatial scales. Spatial measures incorporated the effects of area at different ecological scales (nest site, territory, and landscape) to include ecologically meaningful extents. Temporal measures included seasonal and annual effects, and were designed to detect lagged responses should they occur. Local-to-landscape scale effects of mechanical restoration treatments on local extirpation and abundances of nine species indicated most were insensitive to changes in habitat quality, while abundance models showed only broad declines. Changing the availability of nesting habitat on both the attractiveness and quality of an area at multiple extents confirmed the need for long-term study effects due to lagged responses in expressed preference and changes to nesting habitat quality. Time since treatment affected nest success in two of the four species, yet the changes in habitat quality did not forecast changes in habitat preference as expected. Non-adaptive mismatches seemingly occurred as habitat preferences indicated treatments may create benign-appearing "sink" habitat for species that remained in the area. The umbrella species concept is misapplied at this scale: each species' response was consistent, but responses varied in scale, timing, and direction among species. Patterns of nest density and nest site descriptions demonstrated population-level movement in response to treatments, suggesting half the focal species moved nest sites to remaining habitat areas. Larger scale responsive movements were observed in the remaining species, both out of and into the nest plot. Descriptions of nesting habitat characteristics for the focal species tested if the selected nesting habitat was consistent between pre- and post-treatment, and determined which habitat characteristics, including distance to disturbance, were related to nest success. Descriptions of nesting habitat characteristics support previous work in terms of structural characteristics. Habitat selection was consistent even when the available habitat was not, implying these species choose sites and are not merely settling randomly. However, selected nesting habitat was not strongly tied to nest success at local scales and nest success was negatively related to landscape qualities that treatments were designed to enhance.