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First published online December 14, 2007
Journal of Experimental Biology 211, 58-65 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.009811
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A new method to quantify prey acquisition in diving seabirds using wing stroke frequency

Katsufumi Sato1,*, Francis Daunt2, Yutaka Watanuki3, Akinori Takahashi4 and Sarah Wanless2

1 International Coastal Research Center, Ocean Research Institute, The University of Tokyo, 2-106-1 Akahama, Otsuchi, Iwate 028-1102, Japan
2 Centre for Ecology and Hydrology, Banchory, Aberdeenshire AB31 4BW, UK
3 Graduate School of Fisheries Sciences, Hokkaido University, Minato-cho 3-1-1, Hakodate 041-8611, Japan
4 National Institute of Polar Research, 1-9-10 Kaga, Itabashi, Tokyo 173-8515, Japan


Figure 1
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  		Fig. 1. (A) Spectrogram calculated from dorso-ventral acceleration (green line) of a shag (03F4) during an aerial flight for 403 s. (B) Power spectral density calculated during the flight indicates a clear peak at the frequency of 5.563 Hz.

 

Figure 2
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  		Fig. 2. An example of dives (black line), dorso-ventral acceleration (green line) and pitch angle (grey line) of a shag (03F4) during a foraging trip between two landings. Periods ashore in the colony, in flight and in dive bouts are indicated as grey, orange and blue bars at the top, respectively. Values on the orange bars are dominant stroke frequencies (Hz), and values in parentheses are estimated body masses (kg).

 

Figure 3
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  		Fig. 3. Mass gain in each dive bout in relation to (A) dive duration and (B) cumulative dive duration. Symbols indicate study year (circles for 2003 and squares for 2006), and colours represent individuals.

 

Figure 4
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  		Fig. 4. Comparison of mass gain in trip with (A) cumulative dive bout duration, (B) cumulative dive duration, (C) cumulative flight duration and (D) flight time back to the colony in each trip. Symbols indicate study year (circles for 2003 and squares for 2006), and colours represent individuals.

 

Figure 5
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  		Fig. 5. Relationships of body mass lost on land to (A) time on land and (B) mass gain in preceding trip. Symbols indicate study year (circles for 2003 and squares for 2006), and colours represent individuals.

 




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