Diving costs as a component of daily energy budgets of aquatic birds and mammals: generalizing the inclusion of dive-recovery costs demonstrated in tufted ducks

Metabolic studies on freely diving birds and mammals are reviewed and allometric relations of diving costs are presented. A distinction can be made between three different types of diving costs: (1) metabolic rate during submergence, relevant in estimating aerobic dive limits, (2) average metabolic rate during diving and breathing intervals (MRd), and (3) diving costs as the excess over resting costs (EDC). EDC is the most comprehensive measure, integrating energy costs over entire dive series with subsequent longer term recovery from heat loss or anaerobic metabolism. Respirometry experiments with tufted duck (Aythya fuligula) diving in a 5.7 m deep indoor tank demonstrated that in this species diving costs, expressed as EDC, increased at lower water temperatures. MRd was not significantly related to temperature, and probably reflects only the hydrodynamic and not the thermoregulatory component of diving costs. In general, the usual practice of measuring metabolic costs only during diving activity seems ...