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Tufted ducks, Aythya fuligula, were trained to dive for different durations in shallow tanks using a computer-controlled system of lights. The birds were rewarded with food for a correct response, i.e. performing a dive of the required duration. When dive durations (td) elicited by the system were longer than the durations required, the extra time was spent feeding. As the required duration was increased, so the time spent feeding decreased, and the required and actual dive durations approached equality. This occurred at approximately 40 s, although some birds did perform dives of up to 45 s. Heart rate (fH) and oxygen consumption (VOO2) were measured from the birds during voluntary diving using an implanted radiotransmitter and respirometry, respectively. The oxygen consumption during submersion decreased with increasing mean (td, and may reflect a reduction in aerobic metabolism as a dive progressed, possibly as a result of reduced buoyancy or through a gradual switch to anaerobic metabolism. Over a total dive cycle (the time spent submerged plus that spent on the surface between dives), fH proved to be a very good predictor of VOO2, with an error of only +7.9 %. This compares favourably with other methods used to determine the energy expenditures of animals, e.g. the doubly labelled water and the time energy budget methods, and shows that the electronic acquisition of fH could be a useful tool for estimating the energy usage of free-living, aquatic birds.

A Method for Controlling the Feeding Behaviour of Aquatic Birds: Heart Rate and Oxygen Consumption During Dives of Different Duration