Nectar feeding, diuresis, and electrolyte replacement of hummingbirds
Abstract
Hummingbirds depend on floral nectars for energy. This entails a significant water excess which is eliminated in chronic diuresis. In the eight species from which we obtained urine samples, solutes were conserved by reducing urine osmotic concentrations to approximately one-fifth of plasma levels. Sodium and potassium salts accounted for one-half to one-third of the osmotic concentration of urine. These salts can be replaced mostly from trace amounts in the floral nectars. Data from field, laboratory, and the literature are combined to account for salt and water exchanges of broad-tailed and rufous hummingbirds. Published accounts of avian renal morphology and physiology are consistent with hummingbird urinalysis.
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