27 June 2013

New paper on flight speeds of birds

When we wish to calculate how far a bird can migrate given a certain fuel load, or how fast a bird is expected to fly in a specific context (such as display, foraging or migratory flight), we often make use of flight mechanical theory. The backbone of this theory is the U-shaped relationship between power required to fly and the flight speed through the air (airspeed). The theory was developed/adapted for bird flight more than 40 years ago by the English scientist Colin Pennycuick. Over the years Colin has amended the theory by various experiments and measurements, often involving wind tunnels. Accurate predictions from this theory rely on a number of parameters that describe the aerodynamic properties of the avian body and the wings. Some of these parameters, the induced drag factor and the body drag coefficient, have now been explored in the light of new measurements of flight speeds using an ornithodolite. It turns out that birds are probably more efficient in generating the lift than previously assumed, and also that the body drag coefficient (describing how much drag the body is generating) may vary among species. The fieldwork for this study was carried out last autumn by CAnMove scientists together with Colin Pennycuick, who is at Bristol University, using a new ornithodolite consisting of a Vector range finder (a pairs of binoculars with a laser range finder), an anemometer for wind measurements and a computer for data recording. The fieldwork was carried out on the south east coast of Öland during the autumn migration period in 2012, where large numbers of a variety of species migrated. The paper is published in the Journal of Royal Society Interface, and is open access.

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