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

Abstract

ABSTRACT 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 3 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 3 habitats. We found that bird communities responded to water deficit in all 3 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 were 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. LAY SUMMARY Birds of the desert Southwest, a climate change hotspot, are among the most vulnerable groups in the United States and the risk of population declines increases with increasing drought frequency and intensity. Using 12 years of bird monitoring data, we determined how bird communities in 3 distinct habitats (riparian, pinyon-juniper, and sagebrush shrubland) responded to water deficit (a measure of drought stress) in 11 national parks and monuments in the Northern Colorado Plateau. We found that the aridland breeding bird community responses to annual water deficit depended on habitat type. Through the identification of the sensitivity of species to drought stress in specific habitats, land managers can further focus conservation efforts on the habitat in which a species is most vulnerable and prioritize habitat obligate species that show vulnerability to projected climate changes within essential habitat.