Field data
We sampled breeding birds with eight-minute, 100-m fixed-radius point
counts from late May through early July. In the western Great Basin, we
sampled birds from 2012-2020 at a total of 134 points in 10 canyons
(Fleishman 2019a). We sampled 36 points for 8 years, and 121 for ≥5
years. In the central Great Basin, we sampled birds from 2001-2020,
except 2016 and 2017, at a total of 303 points in 25 canyons (Fleishman
2019b). We sampled 230 of these points for ≥10 years. We visited each
point three times during the breeding season, with ca. 10–14 days
between visits, and recorded all birds detected by sight or sound that
were using resources within the point. We excluded fledglings and
juveniles from analyses.
We extracted daily minimum temperature and daily precipitation at each
survey point in each year from the Parameter-elevation Regressions on
Independent Slopes Model data (PRISM,
https://prism.oregonstate.edu/). From these data, which have a
resolution of 4 km, we derived mean daily minimum spring (1 April – 30
June) temperature, cumulative daily winter (1 December – 31 March)
precipitation, and cumulative daily spring precipitation, which we
expected to limit breeding activity and food availability to a greater
extent than temperature means or climate during other times of the year
(Whitehouse et al. 2013, Visser et al. 2015, Messmer et al. 2021).
We used the normalized difference vegetation index (NDVI) to estimate
primary productivity at each point (Wang et al. 2004). NDVI is
correlated positively with avian abundance and species richness in some
arid ecosystems, including the central Great Basin (Seto et al. 2004,
McFarland and Van Riper 2013). We extracted the annual maximum NDVI
value at the centroid of each survey point from 1 March–30 June from
the Application for Extracting and Exploring Analysis Ready Samples
(AppEARS) database (https://lpdaacsvc.cr.usgs.gov/appeears/).
AppEARS derives NDVI from images captured every 16 days at 250 m
resolution by the Moderate Resolution Imaging Spectroradiometer (MODIS).