Effects of Elevation, Fire Age, Burn Severity, And Pre-Fire Vegetation on Post-Fire Sagebrush Songbird Communities

The Sagebrush Biome of western North America has been threatened by a combination of interconnected threats. In the Great and Columbian Basins, a large portion of sagebrush loss has been due to an increase in higher-severity wildfires, caused by invasive annual grasses. As sagebrush declines, numerous wildlife species that rely on the biome have experienced similar trends. Sagebrush-adapted songbirds such as sage thrasher, Brewer's sparrow, and sagebrush sparrow as well as steppe-songbirds, have all experienced population declines. Currently, limited information exists as to how fire severity or recovery affect these songbirds or what resource managers can do to improve their outcomes post-fire. To address these research and management needs, I conducted a large-scale observational study, where I examined how the abundance of sagebrush obligate and steppe-associated songbird species was influenced by fires that occurred in sagebrush habitats in northern Utah and southern Idaho. I conducted multi-species point counts within fire perimeters randomly stratified by elevation, fire age, and initial burn severity, as well as in unburned reference sites. Then, I modeled how each of these factors influenced songbird density. I found that sagebrush-adapted species were more abundant in reference areas, while steppe-associated species showed positive or neutral responses to fire. Within twenty-five years after a fire, many species occurred at similar densities to reference areas. Lower elevation sites and higher severity burns had more pronounced differences in avian densities compared to reference areas. Our results demonstrate that fire can result in a loss of available habitat for sagebrush songbirds, but that many of the species can return to pre-fire densities within twenty years, especially at higher elevations Next, to assess whether pre-fire vegetation affects post-fire songbird abundance, I used remotely sensed data from the Rangeland Analysis Platform from the year before each fire occurred. I compared pre-fire vegetation cover to the densities of Brewer's sparrows, green-tailed towhees, and the steppe-associated species from the previous chapter. I found that all species, except for horned lark, were more abundant in burned areas when pre-fire annual grass cover was lower. Sagebrush-associated species also occurred at higher densities when pre-fire shrub and perennial herbaceous cover were higher. Reducing annual grass cover before an area burns may lead to improved outcomes for many of these songbird species.