Within-talus temperatures are not limiting for pikas in the northern Sierra Nevada, California, USA

The American pika (Ochotona princeps) is a temperature-sensitive lagomorph reported to be in decline in warmer sites in California, Nevada and portions of Utah. Talus is used for denning and retreat habitat by the species. Climate envelope modeling and climate projections suggest the species' distribution will retract in coming decades-but other studies suggest pikas may be resilient in the face of warming by taking advantage of talus as a thermal refuge from warming air temperatures. We investigated the thermal environment of mid to low elevation talus habitats in the northern Sierra Nevada between 2010 and 2012 using automated temperature loggers placed generally 0.5 to 1 m below the talus surface. We found temperatures within talus are rarely challenging to pikas-even in taluses well below the inhabited elevational range of pikas. Occurrence of temperature extremes within talus was only weakly correlated with elevation, and exhibited substantial variation between talus patches. Temperatures deeper in talus than we were able to probe but that pikas can likely reach are certain to be even more stable and less physiologically challenging. Despite buffered temperatures in the subsurface talus environment, we observed multiple instances of pika-accessible, previously-inhabited talus patches that did not support pikas in our surveys. Summer daily maximum air temperatures at these taluses averaged more than 2 degrees C warmer than occupied taluses, and taluses that pikas occupied in some years but not in others were intermediate in temperature. Sites with no evidence of past pika occupancy averaged warmest of all. We suggest aboveground air and surface temperatures, rather than temperatures within talus, pose a greater challenge to pika persistence, through effects on foraging and dispersal. Our results indicate that the thermal refuge provided by talus is likely to be necessary and beneficial to American pikas, but sufficient only to partially offset the ongoing impacts of warming ambient temperatures on waning pika distribution.