Fig. 2. Wing stroke and heave and surge acceleration in a videotaped rhinoceros auklet (RHAU) diving to 3 m depth. (A) Position of the carpal joint relative to the eye, (B) heave (solid line) and surge (dotted line) are plotted against time, and (C) diagram showing the positions of the eye (open circles) and carpal joint (crosses). Crosses along the line for surge in B indicate samples at 32 Hz. The positions of the carpal joint of the left wing were sampled at 0.06 s intervals (numbered 1-9) with the video-image. The positions of the carpal joint in A were shown as the distance (d in C) between the approximate trajectory of the eye and the carpal joint. The unit of distance was 1/10 of the maximum positive distance recorded. Horizontal broken bars in A indicate the duration of downstroke determined with video-image, and horizontal bars in B indicate the periods when the heave acceleration had a positive value.