Peregrine Falcon (Falco peregrinus) Science Article 7
abstract
When diving at prey straight ahead from great distances at high speeds, a peregrine has a conflict between vision and rodynamics: it must turn its head approximately 40 deg 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 rodynamic 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.
VA Tucker, Tucker, K Akers, and JH Enderson, The Journal of Experimental Biology 203, 3755-3763 (2000)