Water and Sodium Turnover in Coastal and Inlnad Populations of the Ash-Grey Mouse, in Western Austrlia

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Abstract
The water and sodium turnovers of a coastal and an inland population of P. albocinereus were studied seasonally. Although the inland habitat receives considerably less rain and sodium than the coastal habitat, water turnover rates were significantly lower only in May and sodium turnover lower only in August. Water influx rates were lowest at both locations during the summer months, positively correlated with the water content of the vegetation and positively correlated with the amount of rain received in the 30 days before each sampling period. Water efflux rates were negatively correlated with urine osmolality. Sodium influx rates were highest during the summer months and were correlated with the sodium content of the vegetation but not with the sodium deposited in the study areas. Sodium efflux rates were positively correlated with the urine sodium concentration. During the dry months, water and sodium influxes are linked; this is not apparent during the wetter months. The utilization of arthropods for food during the summer months is seen as contributing to the maintenance of water balance during a period when the vegetation is low in water. Both populations breed in late spring, with young animals growing during the summer months, and water and sodium influx rates exceed efflux rates during this period.