Ingested water equilibrates isotopically with the body water pool of a shorebird with unrivaled water fluxes

• Main Authors: Visser, G.H., Dekinga, A, Achterkamp, B., Piersma, T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2000
• Subjects: stable isotopes; water fluxes; evaporative water loss; isotope kinetics; DOUBLY LABELED WATER; ENERGY-EXPENDITURE; PHAINOPEPLA-NITENS; WADDEN SEA; CANUTUS; ADAPTATIONS; TURNOVER; BIRDS; KNOTS; Calidris canutus; Red Knot
• Online Access: https://hdl.handle.net/11370/c25b11f4-9057-4e34-ad2e-127dd3eecb75; https://research.rug.nl/en/publications/c25b11f4-9057-4e34-ad2e-127dd3eecb75; https://pure.rug.nl/ws/files/10175718/2000AmJPhysiolRICPVisser.pdf

We investigated the applicability of H-2 to measure the amount of body water (TBW) and water fluxes in relation to diet type and level of food intake in a mollusk-eating shorebird, the Red Knot (Calidris canutus). Six birds were exposed to eight experimental indoor conditions. Average fractional H-2 turnover rates ranged between 0.182 day(-1) (SD = 0.0219) for fasting birds and 7.759 day(-1) (SD = 0.4535) for birds feeding on cockles (Cerastoderma edule). Average TBW estimates obtained with the plateau method were within the narrow range of 75.9-85.4 g (or between 64.6 and 70.1% of the body mass). Those obtained with the extrapolation method showed strong day-to-day variations (range 55.7-83.7 g, or between 49.7 and 65.5%). Average difference between the two calculation methods ranged between 0.6% and 36.3%, and this difference was strongly negatively correlated with water flux rate. Average water influx rates ranged between 15.5 g/day (fasting) and 624.5 g/day (feeding on cockles). The latter value is at 26.6 times the allometrically predicted value and is the highest reported to date. Differences in H-2 concentrations between the blood and feces (i.e., biological fractionation) were small but significant (-3.4% when fed a pellet diet, and -1.1% for all the other diets), and did not relate to the rate of water flux (chi (2)(1) = 0.058, P <0.81). We conclude that the ingested water equilibrated rapidly with the body water pool even in an avian species that shows record water flux rates when living on ingested marine bivalves.