Professor of Biology Tufts University, United States
Abstract: Animal distributions are influenced by an interplay of factors, including physiological adaptations, behavioral responses, and interactions with other species. We treated 151 species of birds in the Mojave Desert as a model system to explore the impacts of thermal vulnerability, abiotic environmental structures (vegetative shade), and burrow availability created by ecosystem engineers to changes to species richness over time. While bird species richness in the Mojave has declined in response to climate change, the small-mammal community has remained stable. It has been proposed that birds are more susceptible to extreme heat due to their inability to burrow underground as small mammals do; however, the fact that birds can use burrows constructed by other species as refugia raises questions about why they are still experiencing negative trends in persistence. To investigate this issue, we used mechanistic models to analyze the importance of underground microclimates to the resilience of bird species in the Mojave Desert. Our results show that climate change should have caused even greater declines in bird species richness than currently observed, even after accounting for aboveground shade. However, assuming birds always find underground refugia resulted in overly optimistic predictions of species richness over time. Instead, the model that best replicated real-world data suggested that bird declines are partly associated with the decline of Mojave Desert tortoise populations (Gopherus agassizii) and the associated loss of their deep, cool burrows, in addition to greater heat exposure from climate change. This study emphasizes the need for conservation initiatives to protect fossorial animals in this desert system if preserving bird species is a goal. It also provides a model for exploring the complex factors shaping animal distributions in a rapidly changing world, highlighting how physiological limits, behavioral strategies, and interspecific dynamics impact species persistence.
