Study area
The Great Basin includes more than 300 mountain ranges and five or more centers of avifaunal differentiation (Behle 1963). Our work focused on two of these centers and six mountain ranges: the Sierra Nevada and Wassuk Range in the Inyo center (henceforth western Great Basin), and the Shoshone Mountains, Toiyabe Range, Toquima Range, and Monitor Range in the eastern center (henceforth central Great Basin) (Figure 1). We collected data in 35 canyons in these six mountain ranges. The elevation gradient of our study canyons collectively ranged from 1650 to 3200 m. Our study areas generally are not used for agriculture and have little infrastructure, such as roads and buildings, which can greatly affect faunal composition and movement (Fahrig et al. 2009, Theobald et al. 2012, Clucas and Marzluff 2015), allowing for greater confidence in attributing changes in species’ elevational distributions to climate change.
From 1895-2011, mean annual temperatures across the Great Basin increased by an estimated 0.7-1.4°C (Snyder et al. 2019). Temperatures increased in all seasons, especially summer (Tang and Arnone 2013, Snyder et al. 2019). Mean annual temperatures across the southwestern United States, including the Great Basin, are projected to increase by 2.5-3°C, relative to 1971-2000, by the year 2065 (Abatzoglou and Kolden 2011). From 1951–2013, daily maximum precipitation and annual number of days with precipitation increased across the Great Basin (Xue et al. 2017). Interannual variation in precipitation is projected to increase in the region, as is cool-season (November – March) precipitation (Abatzoglou and Kolden 2011, Iknayan and Bessinger 2020). Furthermore, the frequency of precipitation when minimum temperatures are above 0°C (implying rain rather than snow) is projected to increase by 20-50%, relative to 1971-2000, across much of the Great Basin by the year 2050 (Abatzoglou and Kolden 2011).