ENERGY-EXPENDITURE AND WATER TURNOVER OF INCUBATING RUDDY TURNSTONES - HIGH COSTS UNDER HIGH ARCTIC CLIMATIC CONDITIONS

To investigate whether shorebirds breeding in the High Arctic have rel atively high rates of energy expenditure due to the harsh climatic con ditions that prevail even in summer, we measured daily energy expendit ure (DEE) and water turnover of Ruddy Turnstones (Arenaria interpres) during the incubation phase on Rowley Island in Foxe Basin, N.W.T., Ca nada, at 69-degrees-N, using the doubly-labeled-water technique. Simul taneously, we conducted detailed measurements of ambient climatic cond itions, including in situ measurements with heated taxidermic mounts. A series of 11 doubly-labeled-water measurements with eight individual Ruddy Turnstones, of which at least seven successfully hatched eggs, yielded a mean DEE of 4.08 W. This is a relatively high value for a 10 8-g bird, equalling four times their basal metabolic rate (BMR). Most variation in DEE was attributable to standard operative temperature, w hich combines the effects of air temperature, wind and radiation on he at loss from the turnstone's point of view. On average, 25% of DEE was attributable to BMR, 31% to the cost of thermoregulation, and 44% to the cost of activity. The average value for water turnover of 96.6 g/d ay is high compared to published values for other birds and confirms t he large requirement for food (which is water-rich) of incubating Rudd y Turnstones. An analysis of the climatic conditions prevalent in Foxe Basin during the breeding seasons of Ruddy Turnstones, based on the 3 3-year period 1958-1990, indicated that they faced thermostatic hardsh ips, defined as energy expenditure exceeding the maximum sustained wor king level (estimated at 4.5 times BMR), on 15% of the days. Climatic conditions were most severe in the early 1960s, but have improved sinc e.