Meeting Abstract

58.3  Saturday, Jan. 5  Variability in the use of torpor by two species of pocket mice (Perognathus) in northern Colorado BANTA, M.R.*; DYE, J.L.; Univ. Northern Colorado, Greeley, CO; Univ. Northern Colorado, Greeley, CO marilyn.banta@unco.edu

Hibernation is a common strategy mammals use to conserve energy during cold periods, but it is not a viable strategy for small mammals under approximately 100 g. Instead, small mammals often use daily bouts of torpor to conserve energy. Although the shortgrass prairies in northeastern Colorado are subject to long cold winters, the use of torpor by mammals in this habitat has been poorly studied. We focused our study on two species of pocket mice (family Heteromyidae) found in northern Colorado, the silky pocket mouse (Perognathus flavus) and the plains pocket mouse (P. flavescens). Adults of both species weigh 7-10 g and torpor has been documented in both. We examined torpor use under variable temperature and food availability regimens. Animals were acclimated to laboratory conditions for 5 days at 10&degC. Food consumption (g millet/day) of each individual was measured during this period. Animals were then assigned to an ad lib or a restricted diet treatment. Each animal then spent 4 days at each of 3 test temperatures: 10, 1, and -5&degC. These are all temperatures normally experienced by animals in the field. During a total of 288 test-nights, 68 bouts of torpor were recorded. Eighteen of 24 animals underwent at least 1 bout of torpor, the number of bouts per animal ranged from 0-9, and the length of torpor bouts ranged from 6-16 hrs. Of the 68 torpor bouts, 29 (42.5%) occurred at 10&degC, 27 (40%) at 1&degC, and 12 (17.5%) at -5&degC. At all temperatures, P. flavescens entered torpor more frequently than P. flavus. Despite their small size and low metabolic rates, there was a tremendous amount of variability in the use of torpor both within and among species. The reasons for this variation are not known and will be the subject of future studies.