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New bird /pterosaur flight paper in PLoS ONE

Sato K, Sakamoto KQ, Watanuki Y, Takahashi A, Katsumata N, et al.
(2009) Scaling of Soaring Seabirds and Implications for Flight
Abilities of Giant Pterosaurs. PLoS ONE 4(4): e5400.

The flight ability of animals is restricted by the scaling effects
imposed by physical and physiological factors. In comparisons of the
power available from muscle and the mechanical power required to fly,
it is predicted that the margin between the powers should decrease with
body size and that flying animals have a maximum body size. However,
predicting the absolute value of this upper limit has proven difficult
because wing morphology and flight styles varies among species.
Albatrosses and petrels have long, narrow, aerodynamically efficient
wings and are considered soaring birds. Here, using animal-borne
accelerometers, we show that soaring seabirds have two modes of
flapping frequencies under natural conditions: vigorous flapping during
takeoff and sporadic flapping during cruising flight. In these species,
high and low flapping frequencies were found to scale with body mass 
(massâ0.30 and massâ0.18) in a manner similar to the predictions from 
biomechanical flight models (massâ1/3 and massâ1/6).
These scaling relationships predicted that the maximum limits on the
body size of soaring animals are a body mass of 41 kg and a wingspan of
5.1 m. Albatross-like animals larger than the limit will not be able to
flap fast enough to stay aloft under unfavourable wind conditions. Our
result therefore casts doubt on the flying ability of large, extinct
pterosaurs. The largest extant soarer, the wandering albatross, weighs
about 12 kg, which might be a pragmatic limit to maintain a safety
margin for sustainable flight and to survive in a variable environment.

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