Fig. 12. Modeled changes in mechanical work stroke^–1 against drag, buoyancy, inertia (surge acceleration), and all three combined by a Brünnich's guillemot at a range of mean swim speeds during descent at depths of 10, 50 and 100 m. Vertical solid lines delimit the range of mean speeds observed in free-ranging Brünnich's guillemots (1.4–2 m s^–1, Figs 2 and 3). Vertical dotted line indicates the maximum speed observed in common guillemots swimming horizontally in a tank (about 2.6 m s^–1, Swennen and Duiven, 1991).