Range-wide Persistence of the Endangered Arroyo Toad (Anaxyrus californicus) for 20+ Years Following a General Warming Trend and Prolonged Drought

Climate change and prolonged drought have negatively impacted amphibians in southern California, U.S.A. Due to the severe drought from 2012–2016, agencies and researchers had growing concern for the persistence of the arroyo toad (Anaxyrus californicus), an endangered endemic amphibian in this region. Range-wide surveys for this species had not been conducted for at least 20 years. In 2017–2020 we conducted collaborative surveys for arroyo toads at historical locations. We surveyed 87 of the 115 total sites having historical records and confirmed that the arroyo toad is currently extant in 60 of 87 sites and 19 of 25 historically occupied watersheds. Only detection/non-detection and not population size was recorded, therefore potential declines at the population level could not be assessed. In other amphibian species, body condition has been documented to decrease with a decrease in water availability. To further investigate the drought’s impact on this species, we calculated an average body condition index annually for arroyo toads using allometric measurements recorded from 1996–present. This index was plotted against precipitation records over time. Our data show that body condition did not significantly change during drought years, but hydro-regulation may be masking an effect. Our study suggests that this species shows some resiliency to climate change and drought, and that mitigating invasive species, hydro-modification, and other anthropogenic drivers may currently be the most beneficial strategy for toad conservation. Arroyo toad conservation actions may also provide simultaneous benefits to several other native species that share the same habitat.