Study Design and Field Methods: We conducted point counts using standardized methods (Ralph et al. 1995, Ballard et al. 2003) where a single observer estimates the distance to the location of each individual bird they detect within a five minute time span from a fixed location. Point counts were conducted during the spring/summer breeding season in early to mid-morning when weather conditions were mild. To minimize observer bias, we had different observers conduct surveys on each of the two visits per year, and all biologists were thoroughly trained in survey techniques and bird identification.

Sites in the Lassen National Forest ranged in elevation from approximately 1500 - 2000 meters, while those in The Eastern Sierra Nevada (Inyo National Forest) were located at 2100 - 3000 meters. We used USFS forest inventory data in a GIS framework to identify areas with aspen habitat. Various stratifications were implemented to ensure that visits to the field sites were logistically feasible, so we do not sample areas far from roads (>1km) or on very steep slopes (>30%). Point count locations are a minimum of 220 meters apart, and typically are arranged in transects of up to twelve point count stations.