Olfactory Navigation in Homing Pigeons: Are the Current Models Atmospherically Realistic?

Abstract

True olfactory navigation necessitates that homing pigeons (Columba livia) employ an odor "map" when determining their position relative to the home loft. Two models exist currently to explain the nature of this olfactory map. The "mosaic" map model suggests that pigeons learn a patchwork of olfactory cues by direct experience with local odors and determine displacement from the home loft by recognizing these familiar odors upon release. The "gradient" map model postulates the existence of stable odor gradients that extend over distances of up to 1,000 km. Pigeons learn the home value of an olfactory gradient while growing up, and then determine their positions with respect to home by comparing this learned value with the gradient value detected at the point of release. I analyzed both the mosaic and gradient olfactory map models in light of new data on the long-range transport of atmospheric aerosols. These data, obtained in 1983 as part of the Cross-Appalachian Tracer Experiment (CAPTEX '83), cover the region of New York state where extensive experiments on pigeon homing have been conducted from the Cornell University pigeon loft during the past 18 yr. The CAPTEX '83 data provide the first opportunity to assess accurately the atmospheric plausibility of an odor-based navigation system for homing pigeons flown in the northeastern United States. I conclude that the observed patterns of long-range aerosol transport place important limits on the type of olfactory navigation system potentially utilized by homing pigeons. Moreover, a comparison of the CAPTEX '83 data with meterological information relevant to atmospheric conditions in other geographic locations suggests that regionally specific atmospheric patterns may dictate whether pigeons can reliably employ odors during navigation. This regional specificity is proposed as an explanation for the observed discrepancy between results obtained in olfactory navigation tests conducted in Italy and those performed in the northeastern United States.