WATER METABOLISM AND ESTIMATED FIELD WATER BUDGETS IN 2 RODENTS (CLETHRIONOMYS-GAPPERI AND PEROMYSCUS-LEUCOPUS) AND AN INSECTIVORE (BLARINA-BREVICAUDA) INHABITING THE SAME MESIC ENVIRONMENT

At Ta [ambient temperature] 20.degree. C shrews and voles lose water at about twice the rate predicted from body wt, while the white-footed mouse loses about 1/3 more water/day than predicted. Cold exposure (5.degree. C) caused significant increases in water loss in the 3 species; this increase was due to increased fecal and urinary losses while evaporative loss was not significantly changed; during cold exposure P. leucopus lost much less water than shrews and voles. When drinking water was reduced to the minimum requirements at both 5.degree. C and 20.degree. C, the 3 spp. 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 (2953 mosmol/l) than in shrews (1802 mosmol/l) or voles (1758 mosmol/l), and ability to concentrate urine in these 3 as well as numerous other mammals correlated well with relative medullary thickness of the kidneys. Water budgets for the 3 spp. 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. Shrews and voles, despite their high water requirements, are 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; 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.