Graduate Thesis Or Dissertation

Assessing Sagebrush-obligate Songbird Abundance: Considerations of Landscape-level Threats and Umbrella Species Efficacy

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  • The umbrella species concept is a single-species conservation strategy built on the notion that indirect protections are provided for multiple species that occupy the same area as a single, or umbrella, species. The utility of the umbrella species concept relies on similar associations of abundance, distribution, life history requirements, and threats of umbrella and co-occurring species. Greater sage-grouse (Centrocercus urophasianus, hereafter “sage-grouse”), a sagebrush-obligate species, is a high-profile umbrella species for the sagebrush ecosystem. Empirical evaluations of the sage-grouse conservation umbrella lack consensus. Initial assessments have revealed differences in habitat-specific relationships and responses to threats for sage-grouse and co-occurring species vary by scale. However, direct comparisons linking sagebrush-obligate songbird population performance to sage-grouse metrics are necessary to fully evaluate the utility of the umbrella species concept. From 2018–2020, we surveyed 147 random and 97 sage-grouse locations for three sagebrush-obligate songbird species approximately bi-weekly during the breeding season. Surveys were conducted May through July across 6,458 km2 of sagebrush ecosystem in Baker and Malheur counties, Oregon. Our objective was to evaluate the effects of landscape-level threats to sagebrush-obligate songbirds and to quantify sagebrush-obligate songbird abundance relative to locations available to sage-grouse, sage-grouse use locations, and sage-grouse population and breeding habitat indices throughout five sage-grouse Priority Areas of Conservation (PAC), and across four spatial scales (0.2 km, 0.54 km, 1 km, and 6.4 km). We predicted that sagebrush-obligate songbird abundance would be higher at sage-grouse use locations than locations of sagebrush habitat available to sage-grouse, and that sagebrush-obligate songbird abundance aligns with sage-grouse population and breeding habitat indices. Sage-grouse breeding habitat indices at 6.4 km performed well for predicting the abundance of sage thrasher (Oreoscoptes montanus) and Brewer’s sparrow (Spizella breweri). Vegetation and threat variables and distance to active lek2 was the top model describing Brewer’s sparrow (Spizella breweri) abundance. We observed higher abundance of both sage thrasher and Brewer’s sparrow in available habitat for sage-grouse relative to sage-grouse use locations, but differences were not significant. While our findings at available and sage-grouse locations did not support the umbrella concept, our findings relative to sage-grouse breeding habitat index at 6.4 km support developing literature suggesting that the sage-grouse conservation umbrella may be effective when quantifying indices at large spatial extents, however, additional considerations for co-occurring species may be necessary to achieve overlapping conservation outcomes.
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  • Funding provided by Oregon State University and Oregon Wildlife Foundation.
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