Energetics and Water Economy of the Smallest Desert Mammal

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The physiological and ecological coupling of the desert shrew (Notiosorex crawfordi) to its environment has been examined. Mean standard metabolism between 32 and 36 C equaled 17.12 W·kg⁻¹. Below 32 C metabolic rate increased linearly to a high of 79 W·kg⁻¹ at 10 C. The heat transfer coefficient was 3.05 W·kg⁻¹ · C⁻¹ below 32 C. At 37 C air temperature, heat lost by the evaporation of water equaled one-half of the total metabolic heat production. The kidney medullary thickness of the desert shrew is high, suggesting a considerable urine concentrating ability and only scant urinary water losses. By thus minimizing urinary and respiratory water losses, the desert shrew can maintain water balance without drinking even when some water is required for thermoregulation. The climate space of the desert shrew was determined and found to differ from that of the masked shrew. The desert shrew can tolerate higher temperatures than can the masked shrew in full sunlight (23 vs. 6 C) in its nest (38 vs. 24 C) and under...