An infrasound-based avian navigational 'map'

Abstract

The 'compasses' (solar, star, geomagnetic) that homing pigeons and other migratory birds use to orient during flight are generally understood, but the 'map' sense they need to first determine their homeward direction is not. Atmospheric odor and geomagnetic gradients have been proposed as 'map' cues, but are inadequate and remain controversial. Experiments with frosted lenses indicate that sight can also be ruled out. Laboratory tests, however, show that pigeons can detect infrasound (>0.05 Hz), and such signals travel with little attenuation for 1000s of km through the atmosphere. Results from an acoustic ray-tracing program (HARPA) using daily atmospheric profiles are compared with Cornell pigeon release data for a number of sites in upstate New York. HARPA runs show that homeward infrasonic cues could have arrived at the sites from directions opposite pigeon departure bearings, especially when these bearings were unusual. Such signals possibly arise from ground-to-air coupling of microseisms (∼0.2 Hz) from steep-sided terrain features. Pigeons fly in circular or other patterns after release and might use Doppler shifts at constant velocity to determine the directionality of their homeward infrasonic 'map' cues. © 2013 Acoustical Society of America.