Renal and Lower Intestinal Contributions to the Water Economy of Desert-Dwelling Phasianid Birds: Comparison of Free-Living and Captive Chukars and Sand Partridges

Abstract

Osmotic and ionic concentrations were measured in plasma, ureteral urine, and rectal luminal and voided fluids of sand partridges (Ammoperdix heyi) and chukars (Alectoris chukar sinaica) to determine the possible contributions of the kidneys and the lower intestines to the water economy of these desert-dwelling phasianids. During the summer, after 2-3.5 days (mean = 2.7 days) of water deprivation of captive birds held in outdoor aviaries in the Negev Desert, plasma, urine, rectal luminal, and voided fluid osmolalities increased, as did Na⁺ and Cl⁻ concentrations; K⁺ remained unchanged, while body masses decreased. Free-living birds had most fluid compositions intermediate between those of watered and water-deprived captive birds. Notable exceptions were Na⁺ and Cl⁻ concentrations of urine and voided fluid, which were usually much higher in free-living than in captive birds. The above measurements indicated that neither species was especially short of water and that its members' diet was high in NaCl in the wild. In free-living birds, osmotic concentrations of plasma and urine were higher in sand partridges than in chukars. Plasma and urine concentrations in free-living sand partridges were similar to waterdeprived captive ones, whereas, in free-living chukars, these concentrations were similar to captive watered ones. Maximum ratios of mean urine/plasma osmolalities (1.8-1.9) were found in water-deprived sand partridges and were within the documented range for birds. Comparison of urine, rectal luminal and voided fluid compositions indicated that the lower intestine modifies renal output only slightly before excretion when the birds are somewhat concentrating their urine and have a diet containing more than adequate salt, as was the case with free-living birds. However, there was modification by the lower intestine of urine in captive watered birds; osmotic, Na⁺, and Cl⁻ concentrations were lower in voided fluid than in urine in both species.