Fig. 4. Example of changes in beak angle in a Magellanic penguin during a foraging trip. (A) Beak angle in relation to depth over time with major systematic changes occurring whenever the bird was at the surface (see enlarged quadrats in insets at the top of the figure). The beak movement during the fourth dive is due to feeding. Beak angle (B) just prior to a dive after an extended period of rest at the surface and (C) after a dive and followed by extended rest at the surface. Note that in these two examples the trace of beak angle over time is not symmetrical about its mid-point (cf. A). Arrows show periods when the bird was underwater.