Further evidencee for hibernation of bears

Résumé

Typical mammalian hibernators overwinter with low metabolism (0.01 normal), heartrate(7 bpm), and body temperature (5° C). There is some evidence that bears hibernate like typical small (50-500 g) mammalian hibernators. It is known that bears remain in winter dens for 4-7 months with very little movement and without food, water, urination, or defecation; they show a large reduction in heartrate and a small reduction in core temperature. To gain further evidence, we compared the unique EKG of typical hibernators with the EKG of bears with respect to season, activity, and dormancy. In this study, the EKG of 3 species of bears and of Marmota hibemators was recorded by implanted radio-capsule while they were in winterdens. The EKG of awake typical small hibernators is characterized by a reduced relaxation (QT) interval. It was determined that the 3 species of bears, when awake, also have a reduced relaxation interval (bears 0.14-0.23 second; marmota-species 0.07-0.14 second; man 0.39 second). This finding was interpreted as further evidence that bears are hibernators. Additional findings were that (1) the faster the heartrate of the hibernators, shorter is the relaxation interval; and (2) at a constant heartrate, the relaxation interval of both bears and typical hibernators when nondormant, changes from winter to summer.