A technique to measure the volume of diving birds during voluntary dives |
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Authors: | Gal Ribak |
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Institution: | (1) Technion Autonomous Systems Program, Faculty of Aerospace Engineering, Technion, Haifa, 32000, Israel |
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Abstract: | Buoyancy has a substantial contribution to the total mechanical cost of diving in waterbirds. Most of the techniques currently
employed to estimate buoyancy are based on measuring the volume of carcasses or forcibly submerged birds using the water displacement
(Archimedes) principle. In such techniques, the voluntary control the bird might have over plumage and respiratory air volumes
is neglected. Here, I propose an adjustment to the water displacement measurement that allows the measurement of buoyancy
in real-time from unrestrained live birds diving voluntarily. The novelty and accuracy of the technique lie in using a pressure
sensor to continuously measure the water level inside the dive tank while filtering out the interference from surface waves.
The error of the volume measurement in the proposed technique was only ±2.4%. Feasibility of measurement is demonstrated on
captive Great Cormorants (Phalacrocorax carbo sinensis). The measured volumes of Great Cormorants exceeded predictions made based on the volume of carcasses and on average resembled
values measured from live restrained birds. However the technique highlighted the high variation in buoyancy of live birds
(up to 30%) as a result of small changes in the air volumes taken with the bird underwater. |
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