Graph showing body temperature tracings (solid line) of a thirteen-lined ground squirrel inside an environmental chamber beginning in September and ending in April.

<p>Body temperature was measured using a surgically implanted transmitter. The dashed blue line represents the ambient (environmental) temperature, which is lowered to 5°C on November 1 and raised back to 23°C in March or April depending on the experiment. Periodic interbout arousals (IBAs) are seen as regular spikes in body temperature despite a constant ambient temperature of 5°C. Photographs of animals at four different points during the year are indicated and shown above the graph [70]. Characteristic measurements of body temperature (T_b), oxygen consumption (VO₂), and heart rate (HR) during torpor and IBA are shown above the respective photographs.