The American shrew-mole (Neurotrichus gibbsii) seems to occupy an ecological and evolutionary position intermediate to that of shrews and fully fossorial moles. However, because little is known regarding their physiology, we examined the metabolic rate and thermoregulatory competence of 6 shrew-moles exposed to ambient temperatures ranging from 3 to 34°C with flow-through respirometry. The basal rate of metabolism of N. gibbsii (3.94 ml O2 g−1 h−1; 77.90 J g−1 h−1) was 2.32 times greater than predicted for similar-sized placental mammals and close to that of soricine shrews of comparable mass (10–12 g). Over the entire range of test temperatures, mean body temperature (38.4 ± 0.2°C SE) of this small semiterrestrial talpid was higher and more labile than that of other North American moles but within the range typical for north-temperate soricids. With declining ambient temperatures, shrew-moles exhibited gradual reductions in body temperature and minimal whole-body thermal conductance. In 2 instances, shrew-moles were observed to enter an apparent state of hypometabolism. Whether the observed reductions in body temperature and metabolic rate of Neurotrichus exposed to low ambient temperatures are adaptive energy-conservation mechanisms exhibited during periods of prolonged cool wet weather and food deficits in nature, or simply reflect an inability to proficiently thermoregulate after an extended fast, is currently unknown.
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