Seasonal changes in activity patterns and the adaptive value of haying in pikas (Ochotona princeps)

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Abstract
Seasonal changes in the performance of four behaviors, perching, haying, feeding, and surface activity were studied in two populations of North American pikas (Ochotona princeps) living in Colorado. During late summer and early fall (July–September), haying, the gathering of meadow vegetation followed by storing it in their talus territories, made up almost 55% of the pikas' surface activity. After haying ceased, pikas continued to feed in the meadows until snowpack, cold temperatures, and the absence of surface vegetation made this impossible. Beginning in February, individuals remained under the snowpack feeding on vegetation from their hay piles and on lichens available below the snow. Surface activity was not seen again until May when spring vegetation began to appear. Haying appears to be an adaptive response to environmental unpredictability. Hay piles most likely become critical for survival when harsh weather prevents surface foraging and(or) delays the emergence of new vegetation growth in the spring or early summer. It is suggested that the evolution of territoriality in pikas is related to the need to gather sufficient vegetation to serve as a potential winter food supply during years when the winter season is unusually harsh or prolonged.