Body cooling and its energetic implications for feeding and diving of tufted ducks

Wintering in a temperate climate with low water temperatures is energetically expensive for diving ducks. The energy costs associated with body cooling due to diving and ingesting large amounts of cold food were measured in tufted ducks (Aythya fuligula) feeding on zebra mussels (Dreissena polymorpha), using implanted heart rate and body temperature transmitters. The effects of diving depth and food ingestion were measured in two sets of experiments: we measured body cooling and energy costs of six tufted ducks diving to different depths in a 6-m-deep indoor tank; the costs for food ingestion and crushing mussel shells were assessed under seminatural winter conditions with the same ducks feeding on mussels in a 1.5-m-deep outdoor pond. Body temperature dropped during feeding bouts and increased gradually during intermittent resting periods. The temperature drop increased linearly with dive duration. The rate of body cooling increased with feeding depth, but it was lower again at depths below 4 m. Half of the increment in energy costs of diving can be attributed to thermoregulatory heat production, of which approximately 50% is generated after diving to warm up the body. The excess costs for ducks feeding on large-sized mussels could be entirely explained by the estimated energy cost necessary to compensate the heat loss following food ingestion, suggesting that the heat production from shell crushing substituted for thermoregulation. Recovery from heat loss is probably a major component of the activity budget of wintering diving ducks

Heart rate and oxygen consumption of exercising macaroni penguins.

Twenty-four macaroni penguins (Eudyptes chrysolophus) from three groups, breeding males (N=9), breeding females (N=9) and moulting females (N=6), were exercised on a variable-speed treadmill. Heart rate (fH) and mass-specific rate of oxygen consumption (s(V)over dotO(2)) were recorded from the animals, and both fH and s(V)over dotO(2) were found to increase linearly with increasing treadmill speed. A linear regression equation described the relationship between fH and s(V)over dotO(2), for each individual. There were no significant differences in these regressions between breeding and moulting females. There were significant differences in these relationships between all females and breeding males. fH and s(V)over dotO(2), were recorded from five of these animals for a total of 24 h, When fH was used to predict s(V)over dotO(2), for the 24 h period using the derived regressions, the estimate was not significantly different from the measured values, with an average error of -2.1 %. When fH was used to predict s(V)over dotO(2), for the 5 min intervals used for the calibration in all 24 birds, the estimate was not significantly different from the observed values, and the average error was only +0.47 %. Since the fH/s(V)over dotO(2), relationship was the same during periods of the annual cycle when the animals were inactive/fasting and active/foraging, it seems reasonable that, as long as sex differences are taken into account,fH can be used to predict the metabolic rates of free-ranging macaroni penguins all year round.</p