Fig. 4. Changes of body angle (A,D), frequency of forward thrust (B,E) and swim speed (C,F) with current depth while descending and ascending. To show the trends, only mean values are indicated in the ranges 0–2 m, 2–5 m, 5–10 m, 10–15 m, and so on, based on 100 sample dives from nine birds, though all the data were used in the statistical analyses. Data from dives having bottom depths of each depth rank (0–10 m and so on) are shown separately.