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First published online June 6, 2005
Journal of Experimental Biology 208, 2207-2216 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01639

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Regulation of stroke and glide in a foot-propelled avian diver

Yutaka Watanuki^1,*, Akinori Takahashi^1,, Francis Daunt², Sarah Wanless², Mike Harris², Katsufumi Sato^3, and Yasuhiko Naito³

¹ Graduate School of Fisheries Sciences, Hokkaido University, Minato-cho 3-1-1, Hakodate, Hokkaido, 041-8611, Japan
² NERC Centre for Ecology and Hydrology, Banchory, Aberdeenshire AB31 4BW, UK
³ National Institute of Polar Research, Itabashi-ku, Tokyo,173-8515, Japan

View larger version (13K): [in a new window]   Fig. 1. Attachment of data-logger on bird's back. Diagram shows angle of Y (surge) axis of logger to horizon (), that of body axis to horizon () defined as body angle (negative as the bird descends) and logger attachment angle ().

View larger version (33K): [in a new window]   Fig. 2. Data from a male bird dive. (A) Diving behavior and total surge acceleration (YG), (B) the low frequency component of surge (YL) that was given by filtering total surge (YG) using a two-band low-pass filter, and the body angle (=arcsineYL+logger attachment angle ) and (C) the high frequency component of surge (YH) that was given by subtracting the low frequency component of surge (YL) from total surge (YG).

View larger version (26K): [in a new window]   Fig. 3. Enlarged records of acceleration and body angle during phases of the same dive as in Fig. 1. (A) High frequency component of heave (XH: foot stroke), that of surge (YH: forward thrust) and body angle at the start (0–1 m depth) and, (B) middle of descent phase (28–30 m depth) and (C) those at the bottom phase (40 m depth). The high frequency components were obtained using the three types of low-pass filter, where the end of the first band/the start of the second band were 0.1/0.5 Hz, 1/1.5 Hz and 2/3 Hz, and shown by different types of lines. Thick horizontal bars in heave show power strokes. Circles in the figures for high frequency component of surge indicate forward thrusts (see the text for definition).

View larger version (26K): [in a new window]   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.

View larger version (24K): [in a new window]   Fig. 5. Changes of (A) the foot stroke frequency, (B) the duration of power stroke (open symbols) and glide (closed symbols) and (C) the maximum acceleration of surges (open symbols) and heaves (closed symbols) during descent phase for 17 deep (>40 m) dives from three birds. Different symbols indicate different birds. Effects of depth on the frequency of strokes, duration of power stroke and glide, maximum heave acceleration were significant. To demonstrate these effects, linear regression lines are also given.

View larger version (20K): [in a new window]   Fig. 6. Effects of bottom depth on the mean frequency of forward thrust while descending for each dive. The regression line was significant (r=0.72, F(1,98)=107.41, P<0.001; frequency= 3.61–0.02xdepth in m). Different symbols are data from different birds.