Habitat conversion to agriculture and temperature extremes synergistically erode avian reproductive success across the continental United States

Katherine S. Lauck, Kees W. Hood and Thomas Phillips, Fish, Wildlife, and Conservation Biology, UC Davis, Davis, CA, Alison Ke and Elissa M. Olimpi, Wildlife, Fish, and Conservation Biology, University of California, Davis, Davis, CA, Daniel Paredes, Wildlife, Fish and Conservation Biology, University of California, Davis, Davis, CA, William R.L. Anderegg, School of Biological Sciences, University of Utah, Salt Lake City, UT, Daniel Karp, Wildlife, Fish, and Conservation Biology, University of California, Davis, CA

Background/Question/Methods
Habitat conversion to agriculture is the primary driver of species loss and endangerment. Efforts to increase biodiversity in working landscapes, such as diversifying farm fields or installing nest boxes for cavity-nesting birds, may allow more species to thrive in human-dominated landscapes. However, as climate change progresses, human-dominated landscapes may expose organisms to increasingly severe temperature extremes because converting land to agriculture removes trees that insulate the understory from ambient temperature spikes. Bird species with altricial young are essentially ectothermic for the first few weeks of life, meaning low and high temperatures divert energy from growth to thermoregulation. Thus, the combination of ongoing habitat conversion and climate change-driven temperature spikes may disproportionately reduce avian fitness. We combined Cornell University’s Nestwatch database, which documents 317,147 nests of 287 species over 24 years and 92,896 unique locations across the continental U.S., with daily temperature data and surrounding land cover to explore how temperature extremes and land use interact to affect nest success. We asked whether effects of temperature extremes on avian nesting success varied across land use types (i.e., forest, open natural habitats, agriculture, and urban/suburban). Then, we used daily temperature projections from multiple climate models to project how nesting success may change in the future.
Results/Conclusions
We found that bird nests in agriculture are much more likely to fail during temperature spikes than those in natural areas. Specifically, our models suggested that the probability of fledging at least one chick in agriculture changed from 85% to 45% depending on if chicks experienced the least versus the most extreme temperature spikes during nesting. In contrast, success rates increased with temperature spikes in forested areas. These effects were remarkably consistent across species and across geographies. While nests in warmer regions were more likely to fail when temperatures spiked (relative to cool regions), we saw no evidence that the interactive effect of temperature extremes and land use varied across the continental United States. Unsurprisingly, we also found that nesting success is likely to decline substantially in agriculture with future climate change. Therefore, the capacity of agricultural landscapes to support bird biodiversity may decrease as climate change progresses. In contrast, future nests in forest are likely to have a similar probability of success as past nests. Retaining forest in agricultural landscapes may be an effective conservation strategy to prevent the loss of more species to habitat conversion and climate change.