TORPOR BOUT DURATION DURING THE HIBERNATION SEASON OF 2 SCIURID RODENTS - INTERRELATIONS WITH TEMPERATURE AND METABOLISM

Because it is not known why duration of torpor bouts becomes shorter at the beginning and end of hibernation, this phenomenon was studied in Spermophilus saturatus (200-300 g) and Eutamias amoenus (45-60 g), examining the seasonal change in torpor bout duration during hibernation at a constant air temperature (Ta) of 2°C in relation to: 1) the minimum body temperature (minimum Tb) to which the animals could be experimentally cooled before they maintained a constant Tb or began to arouse, 2) Ta at the time of minimum Tb (minimum Ta), and 3) oxygen consumption (VO2) of torpid individuals at Ta 2°C. Average duration of torpor bouts during the main part of the hibernation season was c11 d in S. saturatus and 8-9 d in E. amoenus; in response to cooling, minimum Tb of both species declined as low as -0.2°C. In early and late hibernation, when torpor bouts were short, minimum Tb, minimum Ta, and VO2 during torpor were higher than in the main part of the hibernation season. -from Authors