I told Marv Breece I would send this abstract to him, but I can't seem to
find his address; I hope no one minds a general posting of it.

Kevin Li
Seattle, WA
e-mail: kevin.li at metrokc.gov


http://www.biologists.org/JEB/201/13/jeb1405.html

This is an abstract on gyrfalcon flight, from the Journal of Experimental
Biology (1998).

Diving speeds and angles of a gyrfalcon (Falco rusticolus)

Vance A. Tucker, Tom J. Cade and Alice E. Tucker

Department of Zoology, Duke University, Durham, NC 27708, USA and The
Peregrine Fund, Inc., 566 Flying Hawk Lane, Boise, ID 83709, USA
Address for correspondence: vtucker at acpub.duke.edu

First published: 11 June 1998

Summary
An optical tracking device recorded the three-dimensional paths of 11 dives
by a 1.02 kg gyrfalcon, trained to dive to a falconer. The dives started at
altitudes up to 500 m above the ground and were inclined at angles of 17-62
? from the horizontal. The falcon controlled its speed during the dives,
rather than simply falling from the sky, and the dives had three phases.
During the first (acceleration) phase, the falcon accelerated to speed
limits between 52 and 58 m s-1 in the seven fastest dives, evidently with
minimum drag, because its accelerations were close to those predicted from
theory for minimum drag. The falcon then began a constant-speed phase by
increasing drag by a factor of 1.3-4.8 while still 100-350 m above the
ground in most dives. The constant-speed phase lasted no more than a few
seconds, and the falcon then began a deceleration phase by increasing its
drag further, this time by factors of 1.7-3.2, and decelerating with a mean
value of -0.95 times gravitational acceleration.

During all three phases, the dive angle was nearly constant or increased
during the deceleration phase, and the falcon made no changes in its body
shape that were obvious through the tracking device telescope except to
reduce its wing span as it accelerated. The falconer, however, was close to
the falcon at the end of the dive and could see that, during the
deceleration phase, the falcon held its wings in a cupped position,
apparently with a high angle of attack and therefore high drag. At the end
of the deceleration phase, the falcon dropped its legs, spread its toes and
finally spread its wings as it approached the falconer.

Although the speeds reported here are the fastest ever measured with known
accuracy in animals, the falcon could theoretically have reached more than
70 m s-1 if it had continued to accelerate with minimum drag until close to
the ground. Even at this speed, it would have had enough altitude to pull
out of the dive before crashing into the ground. Several authors have
estimated that diving falcons reach speeds of more than 70 m s-1, and wild
falcons may reach such speeds when they make long, steep dives upon birds
flying high in the air.

Key words: falcon, flight, diving, gyrfalcon, Falco rusticolus, speed.