Peregrine falcons use two high performance skills - flight speed and visual
acuity - to attack their prey. In a trio of papers, Tucker and his
colleagues model the quantitative aspects of aerodynamic drag, assess the
optimal integration of speed and sight, and present field observations of
falcon flight. Drag, particularly at flight speeds in excess of 50 meters
per second, is minimized by keeping the head aligned with the body, but this
presents a problem: prey of the size of a robin can be seen from a distance
of 1 km only by using the deep fovea, which is oriented at an angle of about
40 degrees from the head axis. Thus, it would be impossible for a falcon to
see its prey while flying straight at it, and keeping the head angled while
flying would increase drag significantly and reduce speed. The solution is
for the falcon to fly along a logarithmic spiral, with head and body aligned
along the line-of-flight at a 40 degree angle from line-of- sight to the
prey, until almost 90 % of the distance has been covered, at which point
binocular acuity is sufficient to guide straight-line attack. Several
summers of observation with computerized tracking equipment at Deer Valley
Ranch, Colorado confirm that peregrine falcons do indeed fly along spiral
paths.
J. Exp. WoL 203,3733; 3745; 3755 (2000).
from www.sciencemag.org SCIENCE VOL290 8 DECEMBER 2000
Dr. William J. Larson
Bill_Larson@csi.com
Institut Monte Rosa
Montreux, Switzerland