Responses of Brewer's and Chipping Sparrows to Water Restriction

Abstract

Physiological capacities of xerophilic Brewer's sparrows (Spizella breweri) and the more mesophilic chipping sparrows (Spizella passerina) for dealing with water restriction were examined. On a diet of millet seeds, hydropenic sparrows of both groups lost body mass over the initial 3-4 days. A few individuals of each species continued to lose mass, but many stabilized at about 75%-85% of their initial value and tolerated 3 wk without drinking. The loss principally involved reductions in absolute amounts of body water and protein. Plasma osmotic pressure, daily food intake, and relative protein and water contents (as percent of lean body mass) did not differ significantly between hydrated and hydropenic Brewer's sparrows. Relative water content of water-restricted chipping sparrows was significantly lower than control values. Brewer's sparrows significantly reduced evaporative and cloacal water loss when prevented from drinking. Construction of water budgets indicates that these reductions are sufficient t...