Water Economy of the White-Crowned Sparrow and Its Use of Saline Water

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Abstract
Gambel white-crowned sparrows captured on their winter range in southern California have unusually high voluntary water intake; this increases directly with concentration up through dilutions of 50% sea water. They can maintain or gain weight on hypotonic drinking solutions (tap water, 12.5 and 25% sea water), but lose weight on hypertonic solutions (37.5 and 50% sea water). When offered choices of drinking solutions, white-crowned sparrows invariably prefer the least concentrated; the only solutions between which they could not discriminate were tap water and 12.5% sea water. White-crowned sparrows lose weight at the rate of about 9% of initial body weight per day when deprived of water, and survive for a maximum of 7 days. There appear to be no unique physiological adaptations that equip white-crowned sparrows for existence in arid regions. Instead, they rely upon ordinary avian capacities and occupy desert areas only during the winter when sufficient water and succulent food are more readily available.