Paul, In the Beever et al (2003) article, you can see that the extirpated sites are primarily located in the northwest corner of Nevada and southern Oregon, so temperature averages for the entire state of Nevada are not particularly informative. In this paper, the authors found that the strongest predictor of extirpation was maximum talus elevation. That is to say that the lowest elevation sites were being lost disproportionately. Given this fact and knowledge of the adiabatic lapse rate, it is not particularly surprising that extirpated sites had 7.7 - 10% higher daily maximum temperatures than those of extant sites during June, July, and August (months during which pika are most actively foraging).
At this point the connection between pika extirpation and temperature is correlative, but there is good evidence that pika are particularly sensitive (physiologically) to even moderately high temperatures (AT Smith. 1974. Ecology 55:1368-1376). Work is now being done by myself and others to explore mechanistic hypotheses. Lucas Moyer-Horner UW-Madison
