Return of the pika: American pikas re-occupy long-extirpated, warm locations

American pikas (Ochotona princeps), small mammals related to rabbits, occur in mountainous regions of western North America, where they live in shattered‐rock habitats (talus). Aspects of their physiology and life history create situations that appear to put pikas at risk from warming climates. Some low‐elevation, warm sites that historically harbored pikas have become extirpated, and the assumption is that these will not be re‐colonized under current climate trends. Unexpectedly, in 2021, we found that pikas had re‐colonized two very warm, low‐elevation, dry sites in eastern California, USA, in the Bodie Mountains and Mono Craters. Resident pikas appear to have been absent at both sites for ≥10 years. These findings suggest that pikas, which are normally diurnally active, are able to overcome thermal dispersal barriers and re‐colonize long‐extirpated sites, perhaps by moving during cool nights. Our data also highlight the often unrecognized suitability of pika habitat in warm regions where the interiors of taluses can remain stably cool even when external air temperatures are hot.

Conservation status of American pikas (Ochotona princeps)

The American pika (Ochotona princeps) is commonly perceived as a species that is at high risk of extinction due to climate change. The purpose of this review is two-fold: to evaluate the claim that climate change is threatening pikas with extinction, and to summarize the conservation status of the American pika. Most American pikas inhabit major cordilleras, such as the Rocky Mountain, Sierra Nevada, and Cascade ranges. Occupancy of potential pika habitat in these ranges is uniformly high and no discernible climate signal has been found that discriminates between the many occupied and relatively few unoccupied sites that have been recently surveyed. Pikas therefore are thriving across most of their range. The story differs in more marginal parts of the species range, primarily across the Great Basin, where a higher percentage of available habitat is unoccupied. A comprehensive review of Great Basin pikas revealed that occupied sites, sites of recent extirpation, and old sites, were regularly found within the same geographic and climatic space as extant sites, and suggested that pikas in the Great Basin tolerated a broader set of habitat and climatic conditions than previously understood. Studies of a small subset of extirpated sites in the Great Basin and in California found that climate variables (most notably measures of hot temperature) were associated more often with extirpated sites than occupied sites. Importantly, upward contraction of the lower elevation boundary also was found at some sites. However, models that incorporated variables other than climate (such as availability of upslope talus habitat) often were better predictors of site persistence. Many extirpations occurred on small habitat patches, which were subject to stochastic extinction, as informed by a long-term pika metapopulation study in Bodie, California. In addition, several sites may have been compromised by cattle grazing or other anthropogenic factors. In contrast, several low, hot sites (Bodie, Mono Craters, Craters of the Moon National Monument and Preserve, Lava Beds National Monument, Columbia River Gorge) retain active pika populations, demonstrating the adaptive capacity and resilience of pikas in response to adverse environmental conditions. Pikas cope with warm temperatures by retreating into cool interstices of their talus habitat and augment their restricted daytime foraging with nocturnal activity. Pikas exhibit significant flexibility in their foraging tactics and are highly selective in their choice of available vegetation. The trait that places pikas at greatest risk from climate change is their poor dispersal capability. Dispersal is more restricted in hotter environments, and isolated low-elevation sites that become extirpated are unlikely to be recolonized in a warming climate. The narrative that American pikas are going extinct appears to be an overreach. Pikas are doing well across most of their range, but there are limited, low-elevation losses that are likely to be permanent in what is currently marginal pika habitat. The resilience of pikas in the face of climate change, and their ability or inability to persist in marginal, hot environments, will continue to contribute to our understanding of the impact of climate change on individual species.

Behavioural plasticity modulates temperature-related constraints on foraging time for a montane mammal

Contemporary climate change is altering temperature profiles across the globe. Increasing temperatures can reduce the amount of time during which conditions are suitable for animals to engage in essential activities, such as securing food. Behavioural plasticity, the ability to alter behaviour in response to the environment, may provide animals with a tool to adjust to changes in the availability of suitable thermal conditions. The extent to which individuals can alter fitness-enhancing behaviours, such as food collection, to proximately buffer variation in temperature, however, remains unclear. Even less well understood are the potential performance advantages of flexible strategies among endotherms. We examined the degree to which individuals altered rates of food collection in response to temperature, and two potential benefits, using the American pika (Ochotona princeps), a temperature-sensitive, food-hoarding mammal, as a model. From July-September 2013-2015, we used motion-activated cameras and in situ temperature loggers to examine pika food-caching activity for 72 individuals across 10 sites in the central Rocky Mountains, USA. We quantified % nitrogen by cache volume as a metric of cache quality, and the number of events during which pikas were active in temperatures ≥25°C as a measure of potential thermoregulatory stress. We found a strong negative effect of temperature on the rate at which pikas cached food. Individual responses to temperature varied substantially in both the level of food-collecting activity and in the degree to which individuals shifted activity with warming temperature. After accounting for available foraging time, individuals that exhibited greater plasticity collected a comparable amount of nitrogen, while simultaneously experiencing fewer occasions in which temperatures eclipsed estimated thermal tolerances. By varying food-collection norms of reaction, individuals were able to plastically respond to temperature-driven reductions in foraging time. Through this increased flexibility, individuals amassed food caches of comparable quality, while minimizing exposure to potentially stressful thermal conditions. Our results suggest that, given sufficient resource quality and availability, plasticity in foraging activity may help temperature-limited endotherms adjust to climate-related constraints on foraging time.

Seasonal temperature acclimatization in a semi-fossorial mammal and the role of burrows as thermal refuges

Small mammals in habitats with strong seasonal variation in the thermal environment often exhibit physiological and behavioral adaptations for coping with thermal extremes and reducing thermoregulatory costs. Burrows are especially important for providing thermal refuge when above-ground temperatures require high regulatory costs (e.g., water or energy) or exceed the physiological tolerances of an organism. Our objective was to explore the role of burrows as thermal refuges for a small endotherm, the pygmy rabbit (Brachylagus idahoensis), during the summer and winter by quantifying energetic costs associated with resting above and below ground. We used indirect calorimetry to determine the relationship between energy expenditure and ambient temperature over a range of temperatures that pygmy rabbits experience in their natural habitat. We also measured the temperature of above- and below-ground rest sites used by pygmy rabbits in eastern Idaho, USA, during summer and winter and estimated the seasonal thermoregulatory costs of resting in the two microsites. Although pygmy rabbits demonstrated seasonal physiological acclimatization, the burrow was an important thermal refuge, especially in winter. Thermoregulatory costs were lower inside the burrow than in above-ground rest sites for more than 50% of the winter season. In contrast, thermal heterogeneity provided by above-ground rest sites during summer reduced the role of burrows as a thermal refuge during all but the hottest periods of the afternoon. Our findings contribute to an understanding of the ecology of small mammals in seasonal environments and demonstrate the importance of burrows as thermal refuge for pygmy rabbits.