Atmospheric propagation modeling indicates homing pigeons use loft-specific infrasonic ‘map’ cues
Results from an acoustic ray-tracing program using daily meteorological profiles are presented to explain ‘release-site biases’ for homing pigeons at three experimental sites in upstate New York where W. T. Keeton and his co-workers at Cornell University conducted extensive releases between 1968 and 1987 in their investigations of the avian navigational ‘map’. The sites are the Jersey Hill and Castor Hill fire towers, and another near Weedsport, where control pigeons from the Cornell loft vanished in random directions, in directions consistently >50 deg clockwise and in directions ∼15 deg clockwise from the homeward bearing, respectively. Because Cornell pigeons were disoriented at Jersey Hill whereas birds from other lofts were not, it is inferred that Jersey Hill lies within an acoustic ‘shadow’ zone relative to infrasonic signals originating from the Cornell loft’s vicinity. Such signals could arise from ground-to-air coupling of near-continuous microseisms, or from scattering of direct microbaroms off terrain features, both of which are initially generated by wave–wave interactions in the deep ocean. HARPA runs show that little or no infrasound from the loft area arrived at Jersey Hill on days when Cornell pigeons were disoriented there, and that homeward infrasonic signals could have arrived at all three sites from directions consistent with pigeon departure bearings, especially on days when these bearings were unusual. The general stability of release-site biases might be due to influences of terrain on transmission of the homeward signals under prevailing weather patterns, whereas short-term changes in biases might be caused by rapid shifts in atmospheric conditions.