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Supplementary to a previous investigation (Wallraff and Neumann 1989), further experiments were conducted with homing pigeons that were either familiar of unfamiliar with the release area, and that had or lacked olfactory access to environmental odours. All four possible pairwise combinations of these factors were tested. The previous results were confirmed, showing that in an unfamiliar area olfactory inputs are necessary for home-related orientation, while in a familiar area both olfactory and non-olfactory information can be utilized and each is more or less redundant as long as the other kind of information is also available. The degree of redundancy of olfactory inputs varies, obviously depending on the pattern of individual local experience.

Two groups of pigeons were kept from fledging time in two cages fully exposed to winds. From time to time, the cage containing experimentals was additionally exposed to an artificial air current coming from a specific direction and carrying a scent of benzaldehyde. When both groups were exposed to benzaldehyde scent during transportation and at the release site, the control birds flew homeward, whereas the experimentals oriented in the direction roughly opposite that from which they were used to perceiving the benzaldehyde at the loft. When benzaldehyde was not applied, experimental pigeons were homeward oriented like controls.

Young pigeons were kept in an aviary from the time of weaning until the time of displacement 3–5 months later. The two compartments of the aviary were differentially shielded by surrounding walls, and birds of both compartments were released simultaneously. During six years, seven types of shieldings were used (Fig. 1). Releases were conducted at four sites in the cardinal directions (distances about 100 and 30 km, respectively). Initial bearings and distributions of recoveries led to the following conclusions (Figs. 3 and 4): 1. Visual shielding of the environment up to about 10° above the horizontal plane does not influence long-distance orientation, provided that the shielding does not also impair the airflow through the aviary. 2. Homeward orientation is drastically reduced if the aviary is surrounded by walls made of glass. 3. Homeward orientation from all four directions persists if the pigeons lived in corridors between two solid walls permitting airflow either along the N-S axis or along the E-W axis. 4. The preferred compass direction (PCD) of pigeons which lived in this aviary in unscreened conditions is SSW. In the initial bearings, this PCD is more pronounced than the tendency toward home. 5. The PCD is reversed to NNE in pigeons which lived in a corridor open at east and west (but is unaffected by a N-S corridor). 6. The results obtained with the corridor aviaries do not support the olfactory navigation hypothesis as it stands so far (cf. Papi, 1976).

1. Pigeons reared in deflector cages show on release a very pronounced bias of their mean vanishing bearings in the predicted direction, confirming the results of Baldaccini et al. (1975a). The angle of deviation though is only about half the angle of actual wind deflection in the cages. The concentration of bearings about the mean direction is significantly smaller than those of controls reared in cages without defectors. 2. The homing speed of the pigeons reared in deflector cages is significantly lower than that of pigeons reared in control cages. 3. Application of an anesthetic (Xylocaine spray, effective during transport and at the release site) onto the olfactory and respiratory epithelia of the nose does not in any significant way influence this ‘deflector effect.’ 4. Plugging the nose with silicone rubber does not affect the ‘deflector effect.’ Homing speed and homing success in pigeons with plugged nares are drastically reduced, in naive as well as in experienced pigeons. 5. It is suggested that the factors involved may not be olfactory ones but of some other physical or chemical nature, mediated or caused by the wind and picked up by some sensory mechanism other than olfaction.

This study compares the orientation of untreated pigeons and pigeons subjected to olfactory deprivation at two lofts near Pisa, Italy, at a loft at Ithaca, New York, USA, and at a loft at Frankfurt a.M., FRG. The experimental birds were rendered anosmic by nasal plugs until Gingicain, a local anaesthetic, was applied shortly before release. The Italian and American control pigeons appeared to orient towards home equally well, while the control pigeons in Germany frequently preferred directions that deviated significantly from the home direction. The effect of olfactory deprivation was small in the USA and in Germany; it was significantly larger in Italy, indicating that Italian pigeons depend on olfactory information to a much greater extent. These findings suggest that there are important regional differences in the strategies and cues pigeons use to navigate. The varied roles of olfactory information, and the reasons for these differences are discussed.

By means of training flights (mostly flock releases), two groups of young homing pigeons were made familar with a larger area asymmetrically extending from the loft toward SW and NE, respectively. Thereafter, birds of both groups were released within each of the training areas with which one sort of birds was familiar (F+), the other unfamiliar (F-). Even the F+ pigeons had never been released at the test site itself (nearest previous release 10 km apart). Half of each group was allowed to smell environmental odors (O+); the other half breathed charcoal-filtered air during transportation and at the release site until a few minutes before release when they were deprived of olfaction by intranasal application of Xylocain (O-). The two test sites were 53 km distant from home. There was little difference in initial orientation as well as in homing performance between pigeons that were allowed to smell natural air and were familiar with the area (F+O+) and those that were privileged in only one respect (F+O- and F-O+). Yet if none of the preconditions was met (F-O-), performances were drastically reduced. The findings show that pigeons make use of two independent homing methods, olfactory navigation (presumably based on a “navigational map”) and non-olfactory pilotage (presumably based on a “topographical map”). The latter method is restricted to a more or less familiar area determined by individual experience. Its boundaries are poorly defined and can be estimated by the experimenter only in rough approximation. Within this area, the homing system takes advantage of more or less redundant inputs. Outside of it, olfactory information seems indispensable.

Pigeons brought up in closed cages deflecting the winds to the left or to the right show, on release, a bias of the mean vanishing directions to the left or right of the mean direction of untreated control birds. The results are in full accord with the findings of Baldaccini et al. (1975).

To test the present hypotheses concerning the functioning of the bird's magnetic compass, pigeons reared near the magnetic and geographic equator (Fortaleza, NE Brasil) were released 300 km NW of their home in the horizontal field at the magnetic equator. Pigeons released in the morning and in the afternoon were roughly homeward oriented whereas pigeons released at noon with the sun near the zenith vanished close to magnetic north. According to the Wiltschko model of the magnetic compass they should not be able to pick up specific directions. A considerable number of young and inexperienced pigeons returned home against a continuously blowing trade wind. This result contradicts the hypothesis of olfactory navigation as currently discussed.