Fig. 8. Derived rate of oxygen transfer from the lungs to the blood (open circles) and cumulative oxygen acquired by the blood (ascending line) during 14 breaths in a single Magellanic penguin that was recovering from a dive lasting 74 s. Tidal volume was taken to be linearly related to maximum beak angle (Table 2) and equivalent to 50 ml deg^–1. Maximum beak angle per breath was taken from the means of presented data (cf. Fig. 5) and corresponding breath cycle times were taken from curve fits derived from Fig. 6 (Table 3). The bird was assumed to breathe through the lungs for the complete cycle time. Total body oxygen storage was taken to be 232 ml (see text). The bird was calculated as having an oxygen debt due to the dive of 163 ml (see text – dotted horizontal lines) and k1 in the equation describing the rate of oxygen transfer (see Equation 7 in text) was nominally given the value of 0.05. (A) A bird having an oxygen debt at the onset of the dive of 57 ml, increasing to 220 ml at the end of the dive. Here, the bird manages to repay the oxygen debt incurred during the dive in full by the end of the surface period. (B) The bird surfacing with an oxygen debt due uniquely to the energy expended during the dive. Here, the bird cannot repay this oxygen debt within the surface pause. (C) Oxygen acquisition as in A (lower line) compared to the acquisition of oxygen by a bird breathing according to the conditions given by the first breath (tidal volume 277 ml and breath cycle 1.2 s) for the full duration of the rest period (upper line). Note here the change in scale on the y-axis.

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