Slithering into the future: environmental influences on habitat use, activity, and reproduction of southern California rattlesnakes

Hayes, William K.

whayes@llu.edu

Department of Earth and Biological Sciences

Loma Linda University

Loma Linda, California USA

Wall, Danielle

High Desert Dani

Landers, California USA

Youngberg, Kimberly A.

Department of Animal Services

Riverside County

Jurupa Valley, California USA

Much of Southern California resides within the California Floristic Province, one of 36 internationally recognized biodiversity hotspots. The region has been deemed the world’s 25th most biologically rich and anthropogenically endangered terrestrial ecoregion. Its two major deserts (Mojave and the Sonoran) have been more impacted by climate change than any other region in the contiguous 48 states, with warming temperatures contributing to chronic severe drought. Increases in temperature and drought can impact snake spatial distribution, physiological performance, reproduction, and behavior. Thus, it is imperative to gain an understanding of how rattlesnake activity and distribution are influenced by environmental variables such as habitat, temperature, humidity, and precipitation. To this end, we analyzed multiple datasets derived from road-based surveys, “nuisance” rattlesnake relocations, and a community science database to explore environmental influences on habitat use, activity, and reproduction of rattlesnakes across the region. Preliminary analyses offer several conclusions. For nocturnal road surveys, year, season, total solar radiation (positive association), average wind speed (negative association), and average air temperature (positive association) exerted significant effects on activity, whereas lunar illumination, wind direction, and precipitation minimally influenced encounter rates. Precipitation, however, was a primary driver of variation in annual road kills, with a gradual decline in mortalities during a prolonged drought and a massive increase in mortalities and reproduction (proportion of neonates and subadults) following winters with heavy precipitation. Rattlesnake activity peaked in spring and fall, in contrast to non-venomous snake activity with a single peak in spring, presumably reflecting differences in mating phenology. Species composition for road kills also varied with precipitation, suggesting there will be winners (rattlesnakes) and losers (other species) with climate change. Collectively, these findings benefit our understanding of how vulnerable rattlesnake populations will be in a region subject to heavy urbanization and a shifting climate, and can inform species and habitat management decisions.