TELEMETRIC INVESTIGATION ON THE HIBERNATION OF EUROPEAN HAMSTERS KEPT UNDER SEMINATURAL CONDITIONS
Thomas Waßmer & Franziska Wollnik, Department of Biology, University of Konstanz, P. O. Box 5560 M618, D-78434 Konstanz, Germany

In each of two winters (1994 / 95 and 1995 / 96), 6 male and 6 female European hamsters (Cricetus cricetus L.) were individually housed in 1.1 x 0.8 x 0.8 m mesh wire cages which were buried 0.6 m into the soil of an outdoor enclosure near the university of Konstanz. From September until May each year, continuous registrations of body temperature (Tb, thermal resolution better than 0.1 °C), localisation of the animal (above ground vs. inside the burrow) and general activity were taken in bins of 5 min. using intraperitoneal temperature-sensitive HF-telemetry and a two antenna receiver system (cage bottom and top).
Due to technical problems and natural mortality a total of only 13 complete and 5 partial hibernation patterns (HPs) could be recorded. 12 hamsters showed a regular pattern of 7 - 44 deep hibernation bouts (HBs) with a decline of Tb down to almost soil temperature (minimum Tb 2.26 °C) and durations > 24 h (maximum 165.5 h) which were separated from each other by short periods of inter-bout normothermy. The HPs of 3 other animals were dispersed with only a few HBs of long duration mixed with shallow HBs of shorter duration. Finally, 3 hamsters did not hibernate: they did not show HBs at all. Hibernation started between October 2 and January 8 and ended between January 29 and April 9. Most hamsters stopped to leave their burrow 4 - 39 days before the first decline of Tb below 30 °C, whereas they maintained inside their burrow for 0.5 - 22 days after the final rewarming in spring. Of the total duration of the hibernation season about 1.6 - 80.2 % were spent in hypothermy (Tb below 30 °C) and 19.8 - 98.4 % in inter-bout normothermy. Mean Tb during hibernation ranged between 13.46 and 37.47 °C, indicating energy savings of 1.2 - 64.7 % during winter (baseline: normothermic values of individual animals before hibernation). Maximum bout duration during hibernation was scattered between end of December and end of March and did not correlate with soil temperature.
7 out of 13 hamsters interrupted hibernation for brief episodes and moved above the ground. During the whole hibernation these animals spent a total of 0.43 - 401.74 h above the ground. General activity was up to 85 % lower as compared to the normothermic conditions before hibernation.
Further analyses on the influence of sex and age on the HPs, food consumption and weight loss during winter, and registration of oestrous cycle in female hamsters through measurements of general activity and Tb after the hibernation period will be presented at the conference.


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