Body temperature patterns of a small endotherm in an extreme desert environment

Most desert small mammals use mechanisms to avoid overheating or dehydration during summer (e.g. nocturnality or torpor), but some are apparently able to cope with higher body temperatures (Tb) than normally recorded for mammals (i.e. hyperthermia). In winter, some small desert mammals use torpor to conserve energy during cool periods. Still, surprisingly few studies have reported field body temperature patterns in small terrestrial mammals inhabiting deserts, so it is unclear how common hyperthermia and torpor are in desert mammals. We measured Tb of a murid rodent, the Libyan jird (Meriones libycus), during both summer and winter in Saudi Arabia. Modal, minimum, and maximum Tbs were higher in summer than in winter, with maximum Tbs near 42 °C during summer, among the highest Tbs ever recorded in wild mammals. Variation in Tb was significantly higher during summer than winter, which was mostly related to passive warming throughout the day as ambient temperatures regularly exceeded 45 °C during summer. Conversely, during winter, Tbs were highest during the nocturnal active period. While the summer Tbs we recorded are among the highest ever for either murids or small desert mammals, we suspect this represents a lack of data on free-ranging small mammals more than unique adaptations by this species.