Torpor Patterns and Microenvironment of the Eastern Chipmunk, Tamias striatus

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Abstract
Four chipmunks (Tamias striatus), implanted with temperature-sensitive radio transmitters, were released into outdoor artificial burrow systems in southeastern Michigan. These systems closely approximated natural burrows in design and dimensions. Torpor patterns, ambient temperatures, and the concentrations of oxygen and carbon dioxide within the burrows were monitored throughout the winter. One animal remained euthermic at all times. The others underwent frequent periods of shallow torpor between December and February. Duration of the torpor cycles was usually less than 24 h, and the mean minimum body temperature during torpor was 16.6°C. The lowest body temperature recorded was 10°C. Nest temperatures during this period were between 2 and 5°C. The nest temperatures were highly stable on a daily basis and never fell below 2°C, whereas temperatures above the surface were frequently below — 10°C. Gaseous composition within the burrows was unstable. Mean oxygen and carbon dioxide concentrations were 17.8 and 3.2%, respectively, but oxygen concentrations as low as 14.4% and carbon dioxide concentrations as high as 6.4% were recorded.