Hans Georg Wallraff

Avian olfactory navigation: its empirical foundation and conceptual state

Abstract Over the last three decades, empirical evidence has been accumulated indicating that displaced homing pigeons, and most likely other birds as well, are able to navigate home by deducing positional information from atmospheric trace gases perceived by olfaction. I briefly describe the most important results leading to this unexpected conclusion and experiments revealing the decisive role of winds at the home site. A hypothesis trying to explain the results proposes that proportional relationships among a number of atmospheric trace compounds (which determine the quality of a resulting odour) show fairly regular spatial distributions with gradient character. Gas-chromatographic analyses of air samples in an area covering 400 km in diameter revealed that differently oriented ratio gradients of volatile hydrocarbons do in fact exist. They are fairly resistant against, but not independent of, changes of wind direction. Using the measured atmospheric data as inputs, a model system is able to simulate homing navigation on a performance level similar to that observed in pigeons. Results of both pigeon experiments and air analyses are incorporated into an earlier (‘preolfactory’) concept of a hypothetical gradient map linked with a sun compass, which is now modified and furnished with more concrete physical substrates. Winds are identified as the crosslink embedding atmospheric ratio gradients into a directional reference scale provided by the periodically moving sun and the geomagnetic field. Kramers ‘map-and-compass concept’ is reconsidered. As crucial questions are still unsolved, olfactory navigation remains a challenge for future research.

Conceptual approaches to avian navigation systems

The general basis of migratory orientation in birds is most probably an endogenous time-and-direction program. Directions are selected with respect to celestial and geomagnetic clues. Using these clues, a bird may reach a large population-specific area; however, it will hardly be able to find a particular location, for instance its previous breeding site. Homing to a familiar site over several hundred kilometres of unfamiliar terrain appears to be based on the smelling of atmospheric trace compounds. Conceptual approaches to the mechanism of olfactory navigation have as yet only reached an early state of speculation.

Olfaction and homing in pigeons: Nerve-section experiments, critique, hypotheses

SummaryAt four sites in the cardinal directions from the home loft in about 180 km distance, 135 experimental pigeons (EPs) and 171 control pigeons (CPs) were released. The EPs had been made anosmic by bilateral olfactory nerve section. All birds were completely inexperienced in homing.Homeward orientation was clearly established in the CPs of which 19% returned to the loft. The performances of the EPs were significantly worse in (a) initial orientation, (b) vanishing intervals, (c) distribution of recoveries, and (d) homing success (none of them homed).The EPs still showed the loft-specific preferred compass direction (PCD).The recoveries of the EPs are much more widely scattered in direction than those of the rather well homeward oriented CPs, even if the distances from the release site are the same in both groups. It is concluded that the navigational capability rather than the motivation to fly or to return home is affected by olfactory deprivation. It is further concluded that homing of pigeons depends on olfactory stimuli perceived at the remote sites even at distances as large as 180km.In the data of the anosmic pigeons a non-olfactory component of homeward orientation persists which is much more pronounced on the W-E axis than on the N-S axis. This component alone appears to be insufficient for a return to the loft.Earlier results and conclusions that gave rise to some controversy are critically examined.The present as well as earlier findings are discussed with respect to two alternative hypotheses of olfactory navigation, the “mosaic hypothesis” (favoured by Papi) and the “gradient hypothesis” (favoured by the author).

Navigation by homing pigeons

Pigeons are able to home from a distant unfamiliar site, even if, during transportation to this site, they were prevented from gathering potentially useful information on spatial configurations of the external world as well as on their own movements. Hence they can deduce information on their current position in relation to home from local clues in an unfamiliar area which may be hundreds of kilometres away from any experienced location. Most likely the birds have analogues of a map and a compass which are used in a process consisting of two steps. For the second step, a fairly well known «sun-azimuth compass» is used; under overcast skies, it may be replaced by a (less well understood) «magnetic compass». Attempts to explain the «map» component, i.e., the mechanism of site localization, on the basis of astronomical or magnetic clues, have been unsuccessful. It has been found, however, that olfactory signals are basically involved. Homing of pigeons from unfamiliar distant sites requires (a) an intact olf...

Endogenous circadian rhythm in cytoplasm of acetabularia: Influence of the nucleus

It was shown by three different methods that in the unicellular and uninuclear green alga Acetabularia the nucleus is capable of determining the phase of the circadian rhythm of the oxygen balance in the cytoplasm.

Does pigeon homing depend on stimuli perceived during displacement? I: Experiments in Germany

SummaryIn order to test whether stimuli perceived during passive displacement are important for the subsequent homing, pigeons were transported in an apparatus designed to prevent them from receiving relevant information: The experimental birds were continuously rotated quite rapidly (1.5 cps, radial acceleration about 4 g); in addition, they were exposed to an artificial magnetic field and supplied with bottled air. Control birds were transported in open-air cages on top of the van with free view to all sides.Five pairs of releases from equal distances in opposite directions were conducted. Experienced birds were released at distances of about 15, 90, and 300 km from the loft, inexperienced birds at distances of about 180km. In each pair of releases both groups of pigeons were significantly homeward oriented. Neither in initial orientation nor in homing performance nor in the distribution of recoveries were the experimental birds inferior to the controls or in any perceptable way different from them.It is concluded that homing of passively displaced pigeons is not primarily based on information gathered during the outward journey.

Preferred Compass Directions in Initial Orientation of Homing Pigeons

The initial bearings of pigeons are commonly not only homeward oriented, but also polarized toward a preferred compass direction (PCD). The PCD is loft-specific; at ten out of eleven loft sites investigated it is in the western semicircle. It can become shifted in the course of general homing experience. The PCD appeared stable against several experimental treatments (long-term clock shifts, olfactory deprivation, exposure to different winds at the home site), but could be reduced or reversed, respectively, by certain screenings of the aviary in which the birds were raised. It is concluded that “release-site biases” are not necessarily caused by distortions of the physical environment.

Does pigeon homing depend on stimuli perceived during displacement

SummarySimilar experiments as described in part I (Wallraff, 1980b) were conducted in Italy. 12 releases at distances of 80–180 km showed, in most cases, similar behaviour of “cueless” transported pigeons and control pigeons, but some gradual difference in the degree of homeward directedness and, at least sometimes, in homing speed. This suggests that, in the area investigated, stimuli perceived during displacement contribute to the orientation behaviour of the birds after release. Usually, however, successful homing does not depend on these stimuli. The experiments suggest the conclusion that there is some (minor) difference in the mode of pigeon navigation in different geographic areas, probably depending on varying environmental conditions.

Social interrelations involved in migratory orientation of birds: Possible contribution of field studies

The question is discussed whether flocking of bird migrants improves the accuracy of orientation toward the intended direction of a population. Statistical implications are described and outlines for possible analyses of field observation data are given. In nocturnal migration of small passerines it is not yet clear whether social relationships exist at all. Suggestions on how to investigate this question are presented.

Über die Heimfindeleistungen von Brieftauben nach Haltung in verschiedenartig abgeschirmten Volieren

SummaryA series of experiments initiated by the lateG. Kramer was continued and evaluated as a whole.1,111 young homing pigeons were placed in aviaries before they could fly. At least three months later they were released individually at distances of 90–100 miles from the loft. 374 birds were recovered; the rest were lost (Table 1).The pigeons raised in relatively free standing „open avaries (O)“ showed a clear homeward orientation (Abb. 11, 12).The homing performances of the pigeons of the following types of aviaries were significantly worse than the performances of the birds of these open aviaries (Table 3), and there is no evidence for a connection between their places of recovery and the home loft:1.“Full palisade (P)”. The aviary was surrounded by a wooden wall a little higher than the aviary itself (map of records see Abb. 15).2.“Low crater aviary (KN)”. The aviary was placed in a depression of the ground, thus preventing the pigeons from seeing the horizon (Abb. 14).3.“Palisade with northern gap (NL)”. The wooden palisade was opened to the north allowing a view of most parts of the northern semicircle (Abb. 16).4.“Palisade with southern gap (SL)”. There was an analogous gap in the south (Abb. 18).5.“Glass palisade (Gl)”. The upper part of the surrounding wall was made of glass. The visual conditions were the same as in the “open” aviaries (Abb. 20). The performances of the pigeons of the following types of aviaries did not differ significantly from the performances of the birds of the „open“ aviaries, and there is a proven or a probable connection between their places of recovery and the home loft:1.“Roofed palisade (Dh)”. The aviary was placed under a wooden roof. Only the lowest parts of the sky could be seen through a narrow slit. The pigeons could never see the sun since the slit was closed from early evening to late morning (Abb. 21). (If the birds were kept in a constant day length of 16 hours their performances corresponded to those of the “bad” aviary group: Abb. 22).2.“High crater aviary (KH)”. The aviary in a depression of the ground was provided with a “second story” enabling the pigeons to have a similar view to the south as from the “palisade with southern gap” (Abb. 17).3.“Palisade with five gaps (5 L)”. The pigeons could see in all directions, although not simultaneously from one point, but only successively from different perching places (Abb. 19). The “palisade effect” can be demonstrated by several different performance criteria which show good agreement with eachother (Abb. 27). It suggests that the barriers between the aviary and the external world interrupt or change a substrate of information spreading in the horizontal plane which is important for homing ability. Its nature is unknown.