Increased drought drives avian community declines in the warm deserts of the United States

The frequencies, intensities, and durations of extreme weather are
increasing under climate change, furthering biodiversity loss. In the
Southwestern USA, rising drought frequencies and intensities are
anticipated to increasingly affect wildlife and their habitat.
Particularly in highly arid regions, where species live closer to the
limit of physiological tolerances, increasing drought emerges as a major
threat to biodiversity. Using North American Breeding Bird Survey data
(1998–2022) in combination with the Standardized Precipitation-Evaporation
Index (SPEI), we estimated the effects of short-term (3-month), annual
(12-month), and prolonged (36-month) drought on avian abundance and
species richness in the warm deserts of the USA. We assessed
community-level drought effects using six Bayesian relative abundance and
species richness models. Our results indicate declines in avian community
abundance and richness under multiple drought durations, with the
strongest effects associated with annual droughts. Our models estimated
that in years where annual drought met the threshold of ‘severe’, 9 out of
38 species would have 18–34% declines in relative abundance compared to a
year with long-term average conditions, and species richness would decline
by 10%. Availability of open water slightly mitigated negative drought
effects on the avian community. Our results suggest drought will
increasingly contribute to the collapse of aridland avian communities
through declines in habitat generalists and obligate aridland species.
Beyond mitigating future climate change, developing local adaptation
strategies in arid regions, such as the conservation of water sources,
appears necessary for biodiversity conservation.