Total Body Water and Its Turnover in Free-Living Nestling Glaucous-Winged Gulls with a Comparison of Body Water and Water Flux in Avian Species with and without Salt Glands

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Abstract
Total body water (TBW) and its turnover were measured in free-living nestling glaucous-winged gulls Larus glaucescens. Body mass (BM) was linearly related to age, and TBW was linearly related to BM in nestlings aged 4-38 days. Equilibration of intravenously (i.v.) injected tritiated water (TOH) was complete in ½ h; intraperitoneally (i.p.) injected TOH in 1 hour. TBW, ml = -28.4 + 0.88 BM, g(r² = .99; 48 determinations, TOH dilution in nestling gulls). TBW decreased rapidly at the end of the maturation period with the largest nestlings (5) having TBW of 83.2% BM, which was higher (P < .001) than that of fledglings (5), 73.9% BM, which was higher (P < .025) than that of adults (5), 66.0% BM. TBW by TOH dilution exceeded that by desiccation to constant weight. Tissue tritium retention in growing gulls was negligible. Mean daily water flux (WF) in adult gulls (6) was 18.1% BM, and mean daily nestling water efflux (WE) was 28.6% BM, linearly related to BM over the growth period and the same during rainy and fair periods. Analysis of published data TOH studies showed that species with salt glands tended to have higher TBW and had significantly (P < .05) greater water flux: than species lacking salt glands, .

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