Water Metabolism and Estimated Field Water Budgets in Two Rodents (Clethrionomys gapperi and Peromyscus leucopus) and an Insectivore (Blarina brevicauda) Inhabiting the Same Mesic Environment

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Abstract
At 20 C shrews and voles lose water at about twice the rate predicted from body weight, while the white-footed mouse loses about one-third more water per day than predicted. Cold exposure (5 C) caused significant increases in water loss in the three species, and this increase was due to increased fecal and urinary losses while evaporative loss was not significantly changed; during cold exposure Peromyscus leucopus lost much less water than shrews and voles. When drinking water was reduced to the minimum requirements at both 5 C and 20 C, the three species showed marked reductions in urinary, fecal, and evaporative losses. Minimum water requirements of P. leucopus were much lower than those of shrews or voles. On minimum water regimes urine concentration was significantly higher in P. leucopus (2,953 mosmol/liter) than in shrews (1,802 mosmal/liter) or voles (1,758 mosmol/liter), and ability to concentrate urine in these three as well as numerous other mammals correlated well with relative medullary thickness of the kidneys. Water budgets for the three species were calculated based on energy requirements; diet; the amount of food intake necessary to fulfill the energy requirements; the protein, salt, and water intake resulting from feeding; and obligatory water loss. These calculations revealed: (1) shrews and voles, despite their high water requirements, are in effect forced to consume large quantities of low-caloric and high water-content food with consequent intake of large quantities of preformed water and probably remain in water balance throughout the year; (2) P. leucopus may need to supplement their diet with small amounts of drinking water in the winter, but their summer diet probably supplies sufficient water.