Document Type


Publication Date

Spring 4-27-1965


The research area selected for this study was a 2.7 acre subalpine (10,900 feet) talus slope. Adjacent meadow areas totaled nearly an acre. Ecological studies included a line-transect plant survey to determine the percentage of total cover provided by each species. Of 71 plant species collected on a complete survey, 21 were eaten by pikas. Potential productivity of meadow areas adjacent to the talus was 1073.6 pounds (dry weight) of forage per acre. Fifty-five percent of the available forage was harvested by 15 pikas, averaging 34.5 pounds per pika. On this basis the potential pika population was 27 animals, 12 more than the area supported. Winter temperature measurements in the talus under the snow and in the overlying air layer indicated that a thermal overturn occurred in late January and persisted until late March. A downslope airflow under the snow contributed to supercooling conditions and effected the exchange of the upper air temperatures with those of the lower microclimates. Rock surface temperatures were colder than overlying air and deep talus temperatures, possibly due to Balch Ventilation. No advantage or disadvantage appeared to be conferred upon pikas whose haystacks were buried under snow. The maximum temperature for the year was 72°F. ; the lowest was -18°F. Peak snow depths occurred in February and March. Eighteen different mammals were pika associates, but only coyotes, foxes, martens, and weasels were potential predators. Thirty bird species were noted in pika habitat; eight of these were potential pika predators. Predation was considered insignificant, although juvenile pika remains occurred in coyote scats. Individual pikas were tagged to facilitate ethological observations. An intensive study of pika interactions revealed that pair-bonding of adult males and females persisted only during the breeding season, with dispersal of the young resulting from the mutual intolerance that developed between adults and young soon after the latter became independent of parental care. Sibling young separated soon after emergence and displayed territorial behavior at this time. Bodily contact fighting was occasionally observed between adults and between juveniles. Juveniles exhibited vocal submissive behavior in response to adult aggression. Differences in juvenile and adult pelage colorations suggested a criterion by which adults and juveniles could be censused in late summer. Two pelage molts were observed—summer and fall. Females molted last, suggesting a criterion for determining sex ratios among adults in late July. A study of vocalization revealed six different calls. Some were analyzed electronically with soundspectrographs. Tonal variation in vocalization among different geographic races of pikas was discussed. The principal pika activity periods occurred in early morning and late afternoon daylight. Feeding and haying behaviors differed. Adult haying activity began in mid-June and continued late into the autumn. The first juvenile haying was noted in late August. Front Range pikas always stored forage under cover. All pikas established observation stations. Chemical analyses of residual spring haystack material are presented in tabular form. Pikas probably derived necessary moisture from succulent food. Excessive drinking in captivity might have been caused by a concentrated diet and by displacement behavior. Circumstantial evidence for winter foraging was manifest in pika tracks, snow burrows, fecal droppings, and girdling of vegetation. An Actogram, showing percentages of time devoted to various activities, was drawn after observing one pika through one 15-hour day. Night activity was thought to occur primarily at the haystack sites. Pika home ranges overlapped. Territorialism was exhibited in many ways. Twelve points were suggested as evidence that pikas do not hibernate. Studies of two captive pikas facilitated comparison of captive and wild behaviors. Coprophagy was discussed.