Fig. 9. Mean V_O2 observed after long dives of four tufted ducks. Data were smoothed by taking a three-point moving average. As well as the general exponential decrease in V_O2 over the first 15 s post surface, there is a cyclical aspect to the data. This is highlighted subjectively on the graph (black bars), and is believed to correspond to expiration (peak) and inspiration (trough), occurring at frequencies similar to those recorded by Butler and Woakes (1979) in a diving pochard (Aythya ferina). The arrow indicates the point of inflection for biphasic uptake.