Winter body temperature patterns in free-ranging Cape ground squirrel, Xerus inauris: no evidence for torpor

The body temperature (Tb) of Cape ground squirrels (Xerus inauris, Sciuridae) living in their natural environment during winter has not yet been investigated. In this study we measured abdominal Tb of eight free-ranging Cape ground squirrels over 27 consecutive days during the austral winter. Mean daily Tb was relatively stable at 37.0 ± 0.2°C (range 33.4 to 40.2°C) despite a marked variation in globe temperature (Tg) (range −7 to 37°C). Lactating females (n = 2) consistently had a significantly higher mean Tb (0.7°C) than non-lactating females (n = 3) and males. There was a pronounced nychthemeral rhythm with a mean active phase Tb of 38.1 ± 0.1°C and a mean inactive phase Tb of 36.3 ± 0.3°C for non-lactating individuals. Mean daily amplitude of Tb rhythm was 3.8 ± 0.2°C. Tb during the active phase closely followed Tg and mean active phase Tb was significantly correlated with mean active phase Tg (r2 = 0.3–0.9; P < 0.01). There was no evidence for daily torpor or pronounced hypothermia during the inactive phase, and mean minimum inactive phase Tb was 35.7 ± 0.3°C for non-lactating individuals. Several alternatives (including nocturnal huddling, an aseasonal breeding pattern and abundant winter food resources) as to why Cape ground squirrels do not employ nocturnal hypothermia are discussed.