When Does Previewing the Landscape Affect Pigeon Homing?

The importance of visual landmarks during homing in pigeons (Columba livia) remains a contentious issue. Three experiments which explore the role of visual landmarks at release sites are reported here. The effects of releasing homing pigeons after a 5-minute period in either a clear or an opaque sided release box were investigated. In the clear sided box pigeons were able to observe local surroundings at a release site, but this view was obstructed in the opaque sided box. In experiment 1 pigeons were released from familiar locations close to home (between 2 and 5.6 km): being unable to view landmarks prior to release significantly slowed homing speeds. In experiment 2 pigeons were released at familiar locations further from home (between 8.4 and 10 km): being unable to view landmarks prior to release did not significantly affect homing speeds. In experiment 3 pigeons were trained to home from distant release sites but were tested at closer, unfamiliar sites located on the likely homing routes used by the pigeons in training. No significant difference in homing speeds were observed when pigeons were released from either the clear or opaque sided box. The significance of these results for understanding the role of visual landmarks within a pigeon's familiar area is discussed.     

Light-dependent information: influence of loft conditions on young pigeon’s navigational system

This study compares the initial orientation and homing performance of young inexperienced pigeons following their transportation to near and distant places in total darkness (treatment) and their subsequent release. The birds were housed in two lofts at the Lisbon Zoo. Each loft had its own specific features: the H-loft was exposed to prevailing winds and allowed an unhindered view of the surrounding landscape; the L-loft was protected from the wind and allowed only a partial view of the surroundings. Pigeons used in the release tests were between 6 and 7 weeks old. We found that, in general, the initial orientation of the pigeons was affected by the treatment: following release at near places, there was an increase in the scatter and a decrease the homeward component, suggesting that light-dependent information collected en route was used by young pigeons. The effect of the treatment was only temporary based on the observation that the homing performance was not affected. However, the distance of the release site strongly influenced the homing performances as pigeons appeared to be unable to home when released at locations distant from the loft. Based on the scatter or the homeward component, inter-loft differences were apparent with respect to different median vanishing intervals and the reactions of specific pigeons when subjected to the same treatment (transport in darkness) following release at near and distant places. These findings suggest that light-dependent information collected en route is a component of the young pigeon’s navigational system but that, at the young age of the birds tested here, it is preferentially used in familiar areas. In addition, the importance of the light-dependent information appears to depend upon prior experience obtained in the lofts.     

Learning multiple routes in homing pigeons

The aerial lifestyle of central-place foraging birds allows wide-ranging movements, raising fundamental questions about their remarkable navigation and memory systems. For example, we know that pigeons (Columba livia), long-standing models for avian navigation, rely on individually distinct routes when homing from familiar sites. But it remains unknown how they cope with the task of learning several routes in parallel. Here, we examined how learning multiple routes influences homing in pigeons. We subjected groups of pigeons to different training protocols, defined by the sequence in which they were repeatedly released from three different sites, either sequentially, in rotation or randomly. We observed that pigeons from all groups successfully developed and applied memories of the different release sites (RSs), irrespective of the training protocol, and that learning several routes in parallel did not impair their capacity to quickly improve their homing efficiency over multiple releases. Our data also indicated that they coped with increasing RS uncertainty by adjusting both their initial behaviour upon release and subsequent homing efficiency. The results of our study broaden our understanding of avian route following and open new possibilities for studying learning and memory in free-flying animals.     

Konditionierung verfrachteter Brieftauben: eine ?neue“ Methode zur Analyse der Karte von Brieftauben

Zusammenfassung Es wird vorgeschlagen, mit Hilfe klassischer Konditionierung sowohl die physikalischen Charakteristika als auch die Verteilung der bei der Navigation von Tauben relevanten Faktoren zu überprüfen. Dabei wird ein neutraler, physikalisch eindeutig definierbarer Reiz mit der Heimkehrreaktion verfrachteter Brieftauben verknüpft. In standardisierten Versuchsreihen kann die Schnelligkeit, mit der Tauben die neue Reizmodalität mit der Aufgabe assoziieren, nach Hause zu fliegen, als Maß für die biologische Relevanz des Reizes dienen. Weiterhin kann mit dieser Methode im Freiland überprüft werden, ob die Taube mit einer vorgegebenen Reizmodalität einen Ort, eine Region oder eine Verfrachtungsrichtung assoziiert. Vorläufige Resultate einer laufenden Arbeit zeigen, daß Tauben in Heimkehrexperimenten auf künstliche Reize (im vorliegenden Fall Geruchsreize) konditioniert werden können. Die hiermit erhaltenen Ergebnisse sollten spezifischere Vorhersagen über mögliche Karteninformation erlauben als bisher, die dann experimentell getestet werden können.

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Conditioning of homing pigeons en route and at the release site: a new method to assess the map component

Summary The present study suggests classical conditioning as a possibility to assess the elusive map of the homing pigeon. In classical conditioning a previously neutral stimulus is associated with an already existing response. In case of the study of pigeon homing well defined physical cues (such as odours, magnetic fields or infrasound) can be presented to the pigeons prior to release. After a series of training sessions the pigeon learns to associate a given stimulus with a certain home direction.According to the preliminary results of this ongoing study, pigeons can learn in homing experiments to associate artificial odours with different home directions. Pigeons have been trained to associated amylacetate with releases from different sites located north of home and benzaldehyde with releases from the south. Exchange of the two odours for the experimental pigeons after ten training sessions results in impaired initial orientation and reduced homing speed of experimentals compared to controls when released at new sites.In comparative studies the time needed to achieve a preset level of performance could be used to rate the biological significance of different stimuli for homing. By releasing conditioned pigeons at different sites it can also be tested whether or not the simulus is being associated with a site, a region or a direction with respect to home. With this approach the distribution as well as the physical characteristics of different cues can be evaluated for their potential as information relevant for pigeon homing.

     

Do release-site biases reflect response to the Earth's magnetic field during position determination by homing pigeons?

How homing pigeons (Columba livia) return to their loft from distant, unfamiliar sites has long been a mystery. At many release sites, untreated birds consistently vanish from view in a direction different from the home direction, a phenomenon called the release-site bias. These deviations in flight direction have been implicated in the position determination (or map) step of navigation because they may reflect local distortions in information about location that the birds obtain from the geophysical environment at the release site. Here, we performed a post hoc analysis of the relationship between vanishing bearings and local variations in magnetic intensity using previously published datasets for pigeons homing to lofts in Germany. Vanishing bearings of both experienced and naïve birds were strongly associated with magnetic intensity variations at release sites, with 90 per cent of bearings lying within ±29° of the magnetic intensity slope or contour direction. Our results (i) demonstrate that pigeons respond in an orderly manner to the local structure of the magnetic field at release sites, (ii) provide a mechanism for the occurrence of release-site biases and (iii) suggest that pigeons may derive spatial information from the magnetic field at the release site that could be used to estimate their current position relative to their loft.     

Does Familiarity with the Release Site Influence the Initial Orientation of Homing Pigeons? Experiments with Clock-shifted Birds

Experiments were performed to test whether the familiarity with the release site plays a role in the initial orientation of homing pigeons. Repeated releases of 6 h clock-shifted birds from the same site during the shifting time produced an improvement of their initial orientation: the shift effect decreased progressively. Since in subsequent releases from unfamiliar sites the shift effect reappears, the course correction observed at the familiar site is attributable to local stimuli and not to a general recalibration of the sun compass.     

Multivariate analysis of initial orientation in homing pigeons: Is there a “preferred compass direction”?

The mean vanishing direction of homing pigeons of a given release often deviates from the home direction considerably. Any kind of geographical systematic in these deviations might give us a hint on the distribution of the information involved in the homing process. Analysis of releases arranged symmetrically around the home loft with methods of circular statistics could not resolve the pending question of site-specificity vs. directional effects in the initial orientation of homing pigeons unambiguously. In part, this ambiguity comes about by the facts that

Homing pigeons only navigate in air with intact environmental odours: a test of the olfactory activation hypothesis with GPS data loggers

A large body of evidence has shown that anosmic pigeons are impaired in their navigation. However, the role of odours in navigation is still subject to debate. While according to the olfactory navigation hypothesis homing pigeons possess a navigational map based on the distribution of environmental odours, the olfactory activation hypothesis proposes that odour perception is only needed to activate a navigational mechanism based on cues of another nature. Here we tested experimentally whether the perception of artificial odours is sufficient to allow pigeons to navigate, as expected from the olfactory activation hypothesis. We transported three groups of pigeons in air-tight containers to release sites 53 and 61 km from home in three different olfactory conditions. The Control group received natural environmental air; both the Pure Air and the Artificial Odour groups received pure air filtered through an active charcoal filter. Only the Artificial Odour group received additional puffs of artificial odours until release. We then released pigeons while recording their tracks with 1 Hz GPS data loggers. We also followed non-homing pigeons using an aerial data readout to a Cessna plane, allowing, for the first time, the tracking of non-homing homing pigeons. Within the first hour after release, the pigeons in both the Artificial Odour and the Pure Air group (receiving no environmental odours) showed impaired navigational performances at each release site. Our data provide evidence against an activation role of odours in navigation, and document that pigeons only navigate well when they perceive environmental odours.     

The Orientational Consequences of Flocking Behaviour in Homing Pigeons,Columba livia

Two experiments are described which investigate the orientational consequences of flocking in homing pigeons Columba livia. Previous experiments have shown that homing pigeons placed inside a clear-sided release box for 5 min before release from a familiar site have enhanced ground homing speed compared with those placed in an opaque-sided box. It is assumed that previewing the surrounding landscape allows for faster homing since a bird denied this information must accumulate the knowledge on release. In experiment 1, using the same technique developed in these experiments but releasing the birds in pairs we showed that within familiar areas, homing pigeons can exploit a partner that has acquired more information, allowing them to home more quickly. In experiment 2 we attempted to test three potential strategies which may occur during homing flights. The results do not conclusively distinguish between these three mechanisms but suggest that orientation of the pairs of birds is most likely to have resulted from a compromise of individual tendencies, or from following the best homer, but not from following a ‘governing leader’. The consequence of these mechanisms is discussed.     

Pigeon homing and magnetic fields: a response to Luschi et al. (1996)

This paper comments on an article ''Pigeon homing: evidence against reliance on magnetic information picked up en route at release sites'' by P. Luschi, C. del Seppia, E. Crosio and F. Papi, which appeared in this journal. It is pointed out that the particular effects which these authors show to be stress-induced artefacts are restricted to their specific strain of homing pigeons. The same effects could not be observed in pigeons from two other lofts: a difference in response that was shown to have a genetic base. In view of this, conclusions drawn from the results of Luschi et al. must be restricted to their own findings; they cannot be generalized to the other findings which indicate the use of magnetic outward journey information in young homing pigeons.     

Temporal fluctuations of the geomagnetic field affect pigeons’ entire homing flight

Tracks of pigeons, recorded with the help of GPS-receivers from two sites 30 km north and south of the Frankfurt loft, were analyzed in view of an influence of irregular fluctuations of the geomagnetic field. The data obtained were correlated with indices characterizing different aspects of these fluctuations. We found the best correlations with the index quantifying the average amplitude of the magnetic disturbance, and with an index that quantifies the average variability of the magnetic field on the day of release: stronger and more variable fluctuations lead to a counter-clockwise shift of the mean headings during the initial phase at the release site and the following departure phase, but not during the final homing phase leading to the loft. The steadiness of flight was not affected during the initial phase; however, during the later parts of the homing flight, stronger fluctuations, as well as higher variability in the magnetic field led to a marked decrease in steadiness. This continuing effect of magnetic fluctuations indicates that magnetic factors not only affect the beginning, but remain an integral part of the pigeons’ navigational processes during the entire homing flight.     

Mechanisms of visually mediated site recognition by the homing pigeon

The recognition of familiar areas by homing pigeons, Columba livia, is now known to depend at least in part on visual cues. Birds allowed a 5-min preview of the surrounding landscape prior to release home faster than those denied access to such cues, suggesting that recognition is visually mediated. We examined this phenomenon further by asking how memory generated through prior experience with a site is used in recognition. We provided a group of homing pigeons with training experience in which they viewed, through a single transparent vertical face of an otherwise opaque release box, an approximately 140° segment of the landscape for 5 min before release. Training previews were always given from consistent locations and orientations within a release site. Test releases that followed were used to ascertain whether subsequent site recognition necessitated previewing from this already familiar angle and distance, or whether the skill could be extended to novel, nonoverlapping lateral views of the landscape. The results suggested that homing performance was better after presentation of the view recapitulating that seen during training than after showing a novel alternative view. Pigeons may have been using a template of the arrangement of familiar landmarks around the release site as the cue for recognition. The effect, however, disappeared after repeated training, suggesting that repeated release from a site may allow for more extensive visual survey and the memorization of detailed features of the landscape or the extraction of site-specific general features that aid recognition even when a novel view is presented. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

The Role of “Outward-Journey Information” in Homing Experiments with Pigeons: New Data on Ontogeny of Navigation and General Survey

Potentially, homing from distant areas can be based on two different principles of navigation: (1) A path-integration mechanism records and integrates an animal's motions during the outward trip; it is independent of location-specific stimuli. (2) Site localization, by contrast, is performed by deducing the animal's position in relation to home from such stimuli. Hence the first mechanism entirely depends on an uninterrupted flow of “outward-journey information”. The second mechanism may but need not be independent of stimuli recorded during the outward journey. Homing of pigeons is evidently based on site localization. Empirical findings do not support the idea that in experiments using passive displacement path integration is involved in addition or alternatively. Also, there is no reason to assume that very young pigeons transitionally, for only few weeks, apply such a method (as has been concluded by Wiltschko & Wiltschko 1982, 1985, etc.). It is shown that very young pigeons require local olfactory signals for initial homeward orientation as do older birds (Fig. 1). They are not generally better at homeward orientation than older inexperienced pigeons and show similar deviations from home and preferences for a particular compass direction (Table 1, Fig. 2). Olfactory signals appear to be gathered, as good as conditions allow, during any stage of a homing experiment. No fundamental difference can be recognized between olfactory “outward-journey information”, “release-site information”, etc. Signals received at different times and sites before release may contribute by varying proportions to the initial-orientation patterns observed under varying circumstances.     

Acetylcholine as sensory transmitter in crustacea

Summary In an attempt to learn more about the so-called map component in pigeon navigation, nine series of tests comprising 34 test releases were performed at a release site, 89 miles NNE of Ithaca, New York, where Cornell pigeons regularly depart nonrandomly but with a large clockwise deviation from the true home direction. The tests included releases of: (1) experienced pigeons new to the site, under sun; (2) pigeons with previous experience at the site, under sun; (3) experienced pigeons new to the site, under total overcast; (4) pigeons with previous experience at the site, under total overcast; (5) first-flight youngsters, under sun; (6) directionally trained pigeons; (7) pigeons from two other Ithaca-area lofts; (8) pigeons from two more distant lofts; (9) Bank Swallows from an Ithaca colony; (10) clock-shifted pigeons; (11) radio- and airplane-tracked pigeons.The results of these tests indicate that the directional bias of the Cornell pigeons is, in general, not dependent on weather conditions or on the previous experience of the birds. Moreover, a similar bias is shown by both pigeons from other Ithacaarea lofts and Bank Swallows from Ithaca. And a similar bias from their respective home directions is shown by birds from other areas. Clock-shifted pigeons departing more directly toward home have poorer homing success than controls. It is concluded that some environmental factor basic to the avian homing process is rotated clockwise at this release site, that biologically the birds are not making an error but are probably reading correctly a distorted map.I thank Irene Brown and Timothy Larkin for their aid in all phases of this project; Donald Windsor for help in two releases; Charles Walcott and Martin Michener for aid in airplane tracking; J. Downhower for collaboration in the radio tracking and swallow releases; Andre Gobert, Howard French, A. E. Newton, and Ludwig Karl for permitting me to use their pigeons, George Yerdon, Forest Ranger, and Andy Misura, District Ranger, New York State Department of Environmental Conservation, for their cooperation in making the facilities of the Castor Hill Fire Tower available to us; Monica Howland for preparing the drawings; and Bertha Blaker for typing. Research supported in part by NSF Grants GB-13046X and GB-35199X, and in part by Federal Hatch funds.     

Hippocampal ablated homing pigeons show a persistent impairment in the time taken to return home

Summary Homing pigeons were subjected to either hippocampal or control anterior forebrain ablations to examine what role the hippocampus and related structures may play in homing behavior. One year after surgery, the test birds were released from five locations where they had never been before. Both groups were successful in orienting homeward from the release sites, indicating that the hippocampus is not necessary for the neural regulation of a pigeon's map and compass system. Nonetheless, hippocampal ablated pigeons were significantly poorer with respect to the time required to return home, indicating a homing performance impairment. Alternative hypotheses are discussed to explain this result, the most parsimonious being impaired ability on the part of the hippocampal ablated birds to direct a course homeward.     

Altered Orientation and Flight Paths of Pigeons Reared on Gravity Anomalies: A GPS Tracking Study

The mechanisms of pigeon homing are still not understood, in particular how they determine their position at unfamiliar locations. The “gravity vector” theory holds that pigeons memorize the gravity vector at their home loft and deduct home direction and distance from the angular difference between memorized and actual gravity vector. However, the gravity vector is tilted by different densities in the earth crust leading to gravity anomalies. We predicted that pigeons reared on different gravity anomalies would show different initial orientation and also show changes in their flight path when crossing a gravity anomaly. We reared one group of pigeons in a strong gravity anomaly with a north-to-south gravity gradient, and the other group of pigeons in a normal area but on a spot with a strong local anomaly with a west-to-east gravity gradient. After training over shorter distances, pigeons were released from a gravitationally and geomagnetically normal site 50 km north in the same direction for both home lofts. As expected by the theory, the two groups of pigeons showed divergent initial orientation. In addition, some of the GPS-tracked pigeons also showed changes in their flight paths when crossing gravity anomalies. We conclude that even small local gravity anomalies at the birth place of pigeons may have the potential to bias the map sense of pigeons, while reactivity to gravity gradients during flight was variable and appeared to depend on individual navigational strategies and frequency of position updates.     

The Influence of Repeated Releases on the Homing Behaviour of Sand Martins (Riparia riparia)

Data on the effect of repeated releases on the homing behaviour of sand martins released four times from the same site (beyond 50 km from the nesting colony) are presented. The results, obtained by two series of releases, show a progressive improvement of both the initial orientation and the homing performances. When the birds released four times from the same site were displaced in a new site, located roughly at the same distance, but in the opposite direction to the former, they do not change directional preferences with respect to the last experimental release; the homing speeds were also not different to those recorded for birds without any release experience. While the learning of orienting cues can not be excluded, the data point out that the habituation to the handling stress and a form of directional training seem to play a major role in determining the observed behaviour. The familiarity with a site does not seem to improve the homing behaviour of sand martins when released from a different one.     

Accurate route demonstration by experienced homing pigeons does not improve subsequent homing performance in naive conspecifics.

We describe an experiment that uses the grouping tendencies and navigational abilities of the homing pigeon (Columba livia) to investigate the possibility of socially mediated information transfer in a field setting. By varying the composition of paired-release types, we allowed some naive birds to receive an accurate demonstration of the home route whilst others were paired with similarly naive conspecifics. After this 'paired phase', we predicted that if any learning of spatial information occurred then naive members of the former pairs would outperform their untutored conspecifics when re-released individually during the subsequent 'single phase' of the experiment. This prediction was not confirmed. Neither homing speed nor initial orientation was superior in individually released tutored versus untutored birds, despite the fact that both performance measures were better in the earlier 'paired phase' with experienced demonstrators. Our results suggest that although naive homing pigeons clearly interact with their experienced partners, they are unable to transfer any individually useful spatial information to subsequent homing flights.     

Das Richtungsverhalten verfrachteter Brieftauben (Columba livia) im Orientierungsk?fig

The orientation of displaced homing pigeons at the moment of their release was tested using an octagonal orientation cage. Under certain conditions, the cage bearings of old, experienced pigeons show rather good homeward orientation, while the directional choices of young birds are not related to the home direction.     

Homing Strategy of the Eastern Chipmunk,Tamias striatus (Mammalia: Rodentia): Validation of the Critical Distance Model

Fifteen eastern chipmunks, Tamias striatus, were displaced and released 500m away from their nest sites, and their eventual behavior was monitored by means of radio-assisted surveillance. As a rule (allowing for some interindividual variability), the chipmunks left the release site area along a relatively straight course, made a U-turn at a median 60 m from the release site, returned closer to the latter and initiated a pattern of systematic search based on relatively straight forays from and back to the release site area. This overall strategy is consistent with the critical distance model of homing, which was originally proposed on the basis of the homing behavior of another sciund, the red squirrel, Tamiasciurus hudsonicus.