2002 - Midwest Peregrine Falcon Restoration Project

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been accurately measured. In level flight, peregrines are fast but no faster than some
ducks, swifts, and shorebirds. They are not as fast in level flight as gyrfalcons. But the
thing peregrines excel at is diving at high speeds, usually in pursuit of prey. The
maximum peregrine dive speed reported in the literature by Vance Tucker and his
colleagues is 100 meters/second; this works out to 223 mph. Typical dives fall in the
range of 150 to 200 mph. No other organism goes this fast under its own power.
Terminal velocity of a free-falling peregrine-like object has been calculated to be about
220 mph. The most interesting aspect of these fast dives has to do with aerodynamics
and the location of fovea in the eye. Here is the summary from the original paper:
“When diving at prey straight ahead from great distances at high speeds, a
peregrine has a conflict between vision and aerodynamics: it must turn its head
approximately 40 degrees to one side to see the prey with maximum visual acuity at
the deep fovea of one eye, but the head in this position increases aerodynamic drag
and slows the falcon down. The falcon could resolve this conflict by holding its head
straight and flying along a logarithmic spiral path that keeps the line of sight of the
deep fovea pointed sideways at the prey. Wild peregrines, observed with binoculars,
telescopes and a tracking device, did approach prey the size of American robins
(Turdus migratorius) and smaller birds from distances of up to 1500 m by holding
their heads straight and flying along curved paths that resembled the logarithmic
spiral.” (Journal of Experimental Biology, 203:pp. 3755-3763, 2000, authors Vance A.
Tucker, Alice E. Tucker, Kathy Akers and James H. Enderson.)
A long, high-speed dive, then, follows a curved path until the falcon is close
enough to its prey to switch to binocular vision and finish in straight pursuit.