Fig. 8. Modeled changes in mechanical work stroke^–1 (A–D) and cumulative work (cum.; E–H) against drag (A,E), buoyancy (B,F), inertia (surge acceleration; C,G) and all three combined (D,H) during descent, based on dive parameters for a Brünnich's guillemot (BRGU 13; Figs 3 and 6; Table 1) and drag of a frozen Brünnich's guillemot (Fig. 1A). Solid circles are for a dive in which all strokes follow Curve 3 in Fig. 6, and open circles are for a dive in which all strokes follow Curve 4 in Fig. 6; triangles are for a dive in which the bird moves at steady speed with no oscillatory (accelerational) stroking. The total cumulative costs of descent for the three conditions are annotated in the bottom right panel. For work stroke^–1, very high values during the first (7.2 J) and second (5.2 J) strokes are not shown.