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Are the Low Protein Requirements of Nectarivorous Birds the Consequence of Their Sugary and Watery Diet?: A Test with an Omnivore

journal contribution
posted on 01.03.2005, 00:00 by E. Tsahar, Carlos Martinez del Rio, Z. Arad, J. P. Joy, I. Izhaki
Nectar-feeding birds have remarkably low nitrogen requirements. These may be due either to adaptation to a low-protein diet or simply to feeding on a fluid diet that minimizes metabolic fecal nitrogen losses. We measured minimal nitrogen requirements (MNR) and total endogenous nitrogen loss (TENL) in the omnivorous European starling Sturnus vulgaris, fed on an artificial nectar-like fluid diet of varying concentrations of sugar and protein. The MNR and TENL of the birds were similar and even slightly higher than allometrically expected values for birds of the starlings' mass (140% and 103%, respectively). This suggests that the low measured nitrogen requirements of nectar-feeding birds are not simply the result of their sugary and watery diets but a physiological adaptation to the low nitrogen input. We also measured the effect of water and protein intake on the nitrogenous waste form in the excreta and ureteral urine in European starlings. Neither high water intake nor low protein intake increased the fraction of nitrogen excreted as ammonia. Ammonia was excreted at consistently low levels by the starlings, and its concentration was significantly higher in ureteral urine than in excreta. We hypothesize that ureteral ammonia was reabsorbed in the lower intestine, indicating a postrenal modification of the urine.

History

ISO

eng

Language

English

Publisher

University of Wyoming. Libraries

Journal title

Physiological and Biochemical Zoology

Collection

Faculty Publication - Zoology and Physiology

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Faculty Publications - Zoology and Physiology

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