The world record pigeon flight home was set on 15th June 1932. The bird disappeared after being released in Arras, France, and it was not for 24 days afterwards before it arrived back at its original loft in Saigon, Vietnam, after flying 10,640 kilometres (in a straight line). This is the longest known distance and the actual world's record and was reported in the paper "La Prensa" of Barcelona.
How do pigeons find their way? How can they orient themselves for such long distances? What is the secret of the pigeon's navigation? Most probably there is not "just an answer" but a combination of several factors. Scientists and pigeon' fanciers of the entire world are still working on this amazing fact that makes pigeons so fascinating and such useful birds.
There is a very interesting article about pigeon navigation written by Verner P. Bingman (Racing Pigeon Pictorial, September 1993) that explains the actual knowledge on this matter. I hope you find it as interesting as I did.
GeomagnetismGiven the well-documented finding that birds can rely on the earth's magnetic field for compass orientation (Wiltschko, 1983), it is not surprising that hypotheses citing a role for geomagnetism in the functioning of the navigational map of pigeons have also appeared. Interestingly, the possible importance of geomagnetism in permitting a bird to determine its location in space was already suggested long before it was established as compass cue (Yeagley, 1947). The supporting evidence indicating a role for geomagnetism for the navigational map includes:
1 - Correlation between variations in the initial orientation of pigeons following release with naturally occurring fluctuations in geomagnetic field.
2 - Impaired initial orientation of racing pigeons when released within naturally occurring magnetic anomalies.
3 - Disrupted initial orientation following experimentally induced magnetic disturbances.
The results of these studies link magnetic stimuli with pigeon homing performance. The effects are plausibly attributed to affect a map mechanism rather than compass orientation, as the experiments are performed under sunny conditions when the birds are known to rely on the sun for compass orientation. However, the possibility of an interaction between magnetic stimuli and sun compass orientation, which manifests itself under conditions of magnetic disturbance, cannot be entirely excluded as an explanation for the reported results. Indeed until an experiment is performed whereby manipulating the ambient magnetic field exposed to a bird results in predictable shifts in orientation that are interpretable in the context of a map, uncertainties will remain regarding its importance, and the question of a geomagnetic role in the pigeon navigation map will remain open.
We have discussed olfactory and geomagnetic cues as independent sources of potential map information. It remains conceivable, however, that they may work in some collective fashion to permit a pigeon to locate its position in space. For example, if the map does take the form of a bico-ordinate gradient system, olfactory stimuli may characterise one axis, and magnetic cues could characterise the other. Although this is as yet a highly speculative notion, Wallraff, Papi, Ioalé & Benvenuti, (1986) have reported that olfactory and magnetic stimuli may interact at some level of the homing process. Racing pigeons exposed to oscillating magnetic fields coupled with deprivation of their sense of smell prior to release fail to show the usual deviation away from the homeward direction characteristic of the magnetic field treatment alone (Benvenuti et al, 1982).
Regional and Individual DifferencesGiven the possibility of multiple sensory mechanisms associated with the pigeon navigational map, it seems important to consider to what extent regional differences may account for these findings. The currently available evidence indicates that wherever it has been extensively studied, olfaction plays a critical role in the proper functioning of the pigeon navigational map. Nonetheless olfactory treatments have been reported to be less affective in altering navigational performance in other locations in Germany and the Unites States.
At this time it is important to consider how and why the importance of smells for navigation may vary regionally. Indeed, potential regionally differences could be based on differences in atmospheric dynamics that may render curried odours more or less reliable as sources of navigational information.
The situation with geomagnetism is somewhat more difficult, insofar as it remains unclear to what extent it may be involved in the navigational map. Nevertheless findings indicate that pigeons from different lofts are differentially affected at the same magnetic anomaly.
In looking at baseline individual behaviour performance, pigeons in different regions are not equally good at returning home following release from unfamiliar locations. For example, birds generally perform better in Italy than in Germany. Raising Italian birds in Germany and German birds in Italy has indicated that baseline differences are, at least in part, environmentally based, possibly reflecting differences in the way environmental cues are employed in the formation of a navigational map. The available evidence indicates that such may be the case, supporting Keeton's (1974) belief that environmental factors may determine the extent to close this section by emphasising that current available evidence implicates smell as the primary source of navigational map information, with the demonstration of alternative sources awaiting further empirical support.
Landmark NavigationSo far we have focused on true navigation, or that mechanism that permits a pigeon to approximate its position in space relative to home from places it has never been before. However, when a racing pigeon is in an area where it has been before, either when returning to the loft from an unknown site or when released in a familiar area, it then has available an additional source of potential navigational information in the form of familiar landmarks, which may or may not be visual.
Despite its intuitive appeal, the extent to which landmarks are used by racing pigeons in generating goal-orientated responses has been one of the most empirically elusive issues in avian navigational research. Nonetheless there are strong indications that racing pigeons do use landmarks for locating their position with respect to home when they are in a familiar area but outside the range of direct sensory contact with their loft. Racing pigeons approaching the familiar area around the loft have been recorded to make appropriate course corrections. Pigeons wearing frosted lenses that affect their vision are successful in orienting homeward from a distant, unfamiliar release site, but appear impaired in returning to their loft once they get to within three to six miles. Finally, racing pigeons which are not permitted free-flight experience around their loft prior to their first experimental release, orient homeward from a distant location, indicating an ability to perform true navigation, but are impaired in locating their loft once within its vicinity. This suggests that flight experience is important for adequate local navigation near the loft, presumably by permitting familiarisation with local landmarks.
Another source of evidence indicating that racing pigeons attend to landmarks for navigation comes from experiments where racing birds are initially impaired at orienting homeward from a distant, unfamiliar release site. However, upon repeated exposure to the, now familiar, release site, the birds become better at orienting homeward following the same experimental procedure that originally rendered them impaired. Familiarity with an area enables pigeons to compensate for disruptions in their navigational map, and it seems reasonable to suppose that this familiarity effect is based on the use of landmarks that they had been exposed to. This familiarity effect has been observed under diverse conditions:
1 - Olfactory-deprived pigeons which generally fail to orient homeward from unfamiliar locations, do orient homeward when released from locations they had been previously.
2 - When released within a magnetic anomaly, racing pigeons are often disoriented. However, there is considerable improvement in homeward orientation on subsequent releases from the same anomaly.
3 - Racing pigeons that are clock-shifted, a procedure that result in predictable change in an animal's monitoring of the sun for sun compass orientation, typically display a deviation in orientation with respect to home when released from either familiar or unfamiliar locations. However, they compensate at least partially for that deviation when released under clock-shift conditions a second time from the same location.
These results suggest that racing pigeons do indeed use landmarks for navigation. However, it should be emphasised that they are likely used under normal conditions primarily to locate the loft once in its vicinity, that vicinity depending on the previous experience of a pigeon (perhaps up to fifteen miles to the loft). The possible use of landmarks from distant, unfamiliar locations should be viewed as an auxiliary mechanism to be employed when use of their navigational map is disrupted or has previously been associated with incorrect orientation.
Landmark Navigation - Theoretical ConsiderationsGiven that racing pigeons use landmarks for navigation, it becomes important to consider how they may be used. In the following discussion, we consider landmarks within the context of local navigation near the loft, but the ideas can be generalised to landmarks use at distant familiar locations as well. Two important questions emerge: (a) What is the nature of the spatial or location purposes (e.g., "my location is north of the loft") or are they also employed in guiding orientation response (e.g., "therefore I should fly to this side of the water tower").
With respect to the first question, two possibilities occur. First, pigeons may rely on landmarks in the form of a mosaic map, whereby a pigeon learns the fixed directional relationships of landmarks or landmark complexes with respect to the loft and/or other landmarks. For example, a pigeon relying on such a system, acquired through experience and coded in terms of compass directions, could learn that the water tower lies north of the loft, or perhaps that the water tower lies north-east of the rubbish dump/truck garage complex, with pigeons associating a single compass directions, or a limited set of compass directions, with respect to any given landmark. In this model each landmark is used as an independent source of information. Use of a mosaic landmark map has been hypothesised to occur at familiar release sites where pigeons are able to orient homeward by having presumably associated a site-specific homeward orientation response with a single set of local landmarks during previous visits.
A second possibility is that landmarks are not used independently as signposts, but collectively in the form of an integrated map. Such a system is characterised by the use of at least a subset of the same group of landmarks from effectively any location where sensory contact with them would be possible. Such a mapping system is advantageous because the same pool of landmarks could be used over an infinite number of locations within an area of familiarity. The superiority of such a cognitive mapping system compared to the mosaic system is effective only from specific locations, for example, the water tower, where a pigeon would have had the opportunity to associate a limited set of directional responses with respect to goal areas. The cognitive mapping system confers considerably more flexibility in getting home from anywhere within a known area.
*This series of articles has been adapted from Spatial Navigation in Birds, Chapter 14, Neurobiology of Comparative Cognition". (R. Kesner & D. Olton, eds. 1990, Erlbaum, Hillside, N.J.)
All Pictures © Gary Hardy (1990)
José P Ribas