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).