Salt Tolerance and Water Requirements in the Salt-Marsh Harvest Mouse

Abstract

T HE salt-marsh harvest mouse (Reithrodontomys raviventris halicoetes) Slives in the salt marshes surrounding San Francisco Bay and the lower reaches of the Sacramento River. This small rodent (about 11-17 gm.) is restricted to the Salicornia marshes and is never found in the uplands (Hooper, 1944). The ability of the harvest mouse to live in salt marshes suggests that it is able to tolerate ingestion of bay water and/or the salty saps of the plants, primarily the halophilic Salicornia. Successful utilization of these fluids would require the harvest mouse to produce urine with salt concentrations similar to those reached in the urine of some desert rodents (Schmidt-Nielsen, 1950; Bartholomew and Hudson, 1959; Hudson, 1962). It might also require adaptations which would negate the cathartic effects of the magnesium and sulfate in sea water, which in man cause diarrhea and thus an increased drain on the water reserves (Wolf, 1958). In this study we determined (a) whether the harvest mouse can successfully drink sea water, (b) the effects on body weight of drinking salt solutions of increasing concentrations, and (c) the effect of restricted quantities of fresh water.