Bird Navigation: Has Olfactory Orientation Solved the Problem?

Abstract

Among the hypotheses advanced during the past 40 years to explain bird navigation, the hypothesis of olfactory navigation is currently the focus of attention. The mosaic-map model and the gradient-map model are two operationally different forms of this hypothesis. The necessary olfactory capacities on the part of the bird to discriminate subtle environmental odors qualitatively (mosaic map) or quantitatively (gradient map) have not yet been demonstrated. A number of experiments with homing pigeons (Columba livia), designed to test the olfactory hypotheses, are discussed. Some seemingly positive results have turned out to have non-olfactory causes (deflector aviary experiments). Other results are not in agreement with respective predictions (certain types of shielding), or are inconsistent or ambiguous (detours, multi-cur or selected-cue deprivation during transport, ventilation at the release site). Some unidentified airborne factor has been shown to have a partial role in homing. Olfactory navigation as hypothesized, however, has not been convincingly demonstrated. According to a recent analysis, meterological realities preclude navigation on the basis of olfactory gradients or mosaic maps. Since anosmic birds can home successfully, olfactory navigation, even if its existences is confirmed in some form, may not be the universal solution to the navigation problem.