A habitat-based approach to determining the effects of drought on aridland bird communities

Aridland breeding bird communities of the United States are among the most
vulnerable to drought, with many species showing significant population
declines associated with decreasing precipitation and increasing
temperature. Individual breeding bird species have varied responses to
drought which suggests complex responses to changes in water availability.
Here, we evaluated the influence of water deficit, an integrative metric
of drought stress, on breeding bird communities within three distinct
aridland habitat types: riparian, pinyon-juniper, and sagebrush shrubland.
We used 12 years of breeding bird survey data from 11 National Parks and
Monuments in the Northern Colorado Plateau Inventory and Monitoring
Network (NCPN). We used a multivariate community level approach to test
for the effect of annual water deficit on the bird communities in the
three habitats. We found that bird communities responded to water deficit
in all three habitat types, and 70% of the 30 species-habitat combinations
show significant relationships between density and variation in water
deficit. Our analyses revealed that the direction and magnitude of species
responses to water deficit was habitat dependent. The habitat specific
responses we observed suggest that the adaptive capacity of some species
depends on the habitat in which they occur, a pattern only elucidated with
our habitat-based approach. The direction and magnitude of the
relationships between predicted densities and annual water deficit can be
used to predict the relative sensitivity of species within habitat climate
changes. These results provide the first attempt to determine how the
indirect effect of changes in water availability might affect aridland
breeding birds in distinct habitat types. Linking breeding bird density to
annual water deficit may be valuable for predicting changes in species
persistence and distribution in response to climate change.