Olfactory Cues Perceived at the Home Loft are not Essential for the Formation of a Navigational Map in Pigeons

Abstract

Deflector lofts consist of a 'pinwheel' arrangement of four stationary deflector panels attached to the sides of a cube-shaped cage. These panels are made of wood and Plexiglas and rotate incoming winds in either a clockwise or counterclockwise direction. When released at a distant site, homing pigeons (Columbia livia) raised in deflector lofts exhibit a shift in orientation relative to controls which corresponds to the clockwise or counterclockwise rotation of winds in their loft, suggesting the involvement of wind-borne olfactory cues in pigeon navigation. As part of a long-term study designed to test whether orientation cues other than odors might also be involved in creating the deflector-loft effect, we carried out experiments in upstate New York, USA, in which deflector lofts were modified to reverse the direction of light reflected from the Plexiglas panels while leaving the rotation of winds unchanged. The results indicate that the orientation of pigeons raised as permanent residents of these altered deflector lofts is not influenced by reflected light cues; i.e. they exhibit the same orientation bias as birds raised in the lofts with normal panels. This is in direct contrast to our previous findings that non-resident pigeons kept in the altered lofts for short periods exhibit a reversal of initial orientation compared to birds from the lofts with normal panels. However, when permanent-resident birds are prevented from having a direct view of the horizon sky by the addition of 'anti-cheating' slats (which prevent the birds from seeing beyond the end of each panel), the deflections are either greatly reduced or eliminated entirely, contrary to the predictions of olfactory navigation models. This disappearance of the deflector-loft effect in the presence of anti-cheating slats suggests that the positions of the deflector panels in the two experimental lofts must be differentially influencing important visual orientation cues reaching the birds housed inside. We believe that these cues are probably derived from polarized skylight emanating from the horizon, and that the obstruction of specific regions of horizon skylight by the deflector panels in the two experimental lofts is responsible for a miscalibration of the pigeon's sun compass. This miscalibration, in turn, generates the orientation bias observed for deflector-loft birds. Our findings force us to conclude that, at least for pigeons raised in New York (and perhaps those from other geographical locations as well), olfactory cues perceived at the home loft do not contribute to the formation of the navigational map.