Do bearing magnets affect the extent of deflection in clock-shifted homing pigeons?

When released after clock-shift, homing pigeons fail to orient towards the home direction but display a consistent deflection of their initial orientation due to the difference between the real sun azimuth and the computed azimuth according to the subjective time of each single bird. It has been reported that the size of the observed deflection is frequently smaller than expected and a discussion on the possible factors affecting the size of deflection has emerged. Some authors have proposed that the major factor in reducing the deflection after clock-shift is the simultaneous use of both the magnetic and the sun compasses, giving true and erroneous information, respectively, about the home direction. Therefore, a magnetic disturbance, by impeding the use of the geomagnetic information in determining the home direction, is presumed to increase the size of the deflection up to the levels of the expectation. To test this hypothesis, we released three groups of clock-shifted birds from unfamiliar locations (unmanipulated pigeons, pigeons bearing magnets on their head, and pigeons bearing magnets on their back) together with a group of unshifted control birds. As no difference in the orientation of the three groups emerged, we were not able to confirm the hypothesis of the role of the magnetic compass in reducing the expected deflection after clock-shift.Communicated by W. Wiltschko     

Re-orientation in clock-shifted homing pigeons subjected to a magnetic disturbance: a study with GPS data loggers

Some authors have proposed that homing pigeons are able to correct the error in orientation following a phase-shift treatment by using the magnetic compass reference. They reported that clock-shifted pigeons bearing magnets display a greater deflection compared to magnetically unmanipulated clock-shifted birds. However, this hypothesis tested by recording pigeons’ vanishing bearings has led to contradictory results. The present study reports pigeons’ tracks recorded with a GPS and shows that clock-shifted pigeons bearing magnets displayed a greater deviation through the whole route compared to the magnetically unmanipulated shifted pigeons. Moreover, the analysis of the tracks shows that the birds belonging to both experimental groups stop in coincidence with their subjective night. When re-starting their journey, the birds corrected the clock-shift induced error in orientation, but the magnetically manipulated pigeons were less efficient in doing so. Our results are consistent with the hypothesis that homing pigeons released from unfamiliar location re-orient after clock shift by using the magnetic compass.     

Orientation of homing pigeons at magnetic anomalies

Summary Young homing pigeons released at a site on the edge of a magnetic anomaly and then in the center of the anomaly show better orientation at the anomalous site than birds released there for the first time. To test the possibility that this improvement is the result of birds learning to obtain navigational information at magnetic anomalies, several groups of pigeons were trained at a series of different anomalies, in different directions from their home loft. When these birds were than tested at an unfamiliar anomaly they were disoriented. They showed no evidence of having learned to obtain navigational information at magnetic anomalies. It is suggested that the disorientation seen at anomalies may be due to a disturbance of position-fixing information at the release site.     

Orientation behavior of homing pigeons at the Gernsheim anomaly

Pigeons were released at four release sites within the Gernsheim anomaly, a magnetic 'hill' with a peak 199 nT above the regional reference field and gentle 'slopes' to all sides, situated 44 km south of the Frankfurt loft. Local magnetic conditions at the sites differed in total intensity and in direction and steepness of the intensity gradient. At all sites, the pigeons were well oriented, showing counterclockwise deviations from the home directions that were most pronounced in the western part of the anomaly. There was no systematic difference in orientation behavior or homing performance between the sites within the anomaly and a control site outside. No effect of the local gradient direction was found, nor did the difference in intensity between home loft and the release site affect behavior. This argues against the use of magnetic navigational factors. However, pigeons released for the first time within the anomaly tended to have longer mean vectors with increasingly steeper gradients, which could mean that the birds might somehow have realized the anomalous nature of the local magnetic conditions and ignored them, relying on non-magnetic cues instead.Communicated by R. Gibson     

When does bearing magnets affect the size of deflection in clock-shifted homing pigeons?

Pigeons whose internal clock is shifted by 6 h show deflections from the direction of untreated controls, yet these deflections are often smaller than predicted. Magnets temporarily disabling the magnetic compass increased these the deflections significantly (R. Wiltschko and Wiltschko 2001), indicating a compromise between sun compass and magnetic compass. – Recently, Ioalé et al. (2006) claim that they could not replicate our findings. The reason lies in a difference in the behavior of the clock-shifted pigeons without magnets: in the study of Ioalè et al. (2006), their deflections was already almost as large as that of our pigeons carrying magnets. This difference is probably caused by the limited experience of the pigeons of Ioalè et al. (2006): Their birds, in contrast to ours, had not used their sun’ compass during extended homing flights at various times of the year and, not having been faced with the necessity to compensate the saisonal changes of the sun’s arc, gave the sun compass more weight than our birds did.A comment to the paper by Ioalè, Odetti and Gagliardo (2006) Behav Ecol Sociobiol 60: 516–521.     

Geographical and temporal variability in pigeon homing

Summary Young homing pigeons from the same German stocks were housed in two lofts, one in southern Germany, near Munich, and one in Italy, near Pisa. In the course of 1 year, two synchronized releases at sites 22–25 km NNW and SSE from each of the lofts were conducted every month. The pigeons that returned were released a second time at a site about 75 km east of home.Both initial homeward orientation and homing success were considerably better in Italy than in Germany. Annual cycles, with maxima in summer and minima in winter, were observed in both countries. They were most pronounced in initial orientation in Italy and in homing performance in Germany. Correlations between homing parameters and ambient temperature correspond to the annual cycles, but they do not indicate that the geographical and seasonal differences in homing behaviour are directly caused by actual temperature at the time of release.Our findings (together with earlier ones) suggest that environmental conditions may be variably conducive to the homeward orientation of pigeons according to spatial and temporal variations in the climate.     

Pigeon homing in relation to geomagnetic,gravitational, topographical,and meteorological conditions

Summary Experienced homing pigeons were released at sites unfamiliar to them and with magnetic and gravity anomalies as well as in areas with rather normal fields throughout the FRG (41 releases when sunny, 14 when overcast; Figs. 1–3). The second-order release data were subjected to both univariate and multivariate statistical analysis (stepwise regression, factor analysis). The magnetic field strength and its gradients within the 1-km circle around the release site were determined from aeromagnetic maps of the anomalies of magnetic total intensity. Analogous variables were derived from gravity anomaly maps. It was tested whether the pigeons fly along that gradient to minimize the difference between the magnetic or gravity field at the release site and the loft at maximum rate. Further independent variables described magnetic K index, day-to-day variations of the magnetic components, topography, meteorological conditions, the number of the releases the pigeons had done, and the distance.Over magnetic anomalies widely varying in strength (departing – 250 nT to 300 nT from normal 600 m above ground), extent, and distance from loft, the pigeons vanished with less deviation from the homeward direction and faster than they did in areas with less irregular fields under sunny conditions; this is in contrast to other studies on magnetic anomalies, except one. At sites of gravity anomalies (15–49 mgal), the pigeons were significantly less homeward oriented and homed slower than at less anomalous sites (–9 to 14 mgal).Variables related to gravity were best predictors in 8 and and second predictors in 3 out of 15 regression analyses of the navigational parameters for the releases under sun. Six times the (absolute) amount of the gravity difference between the release site and the loft was selected first (Figs. 7B, C, 8B, C). The results suggest gravity to be involved in navigation as the pigeons' distance measure. Homeward directedness declined with increasing amount of the gravity gradient in the first 12 releases under sunny skies as well as when overcast (Fig. 8A). A preferred compass direction towards north-northeast was determined, being closest to the grand mean vector of the ascending gravity gradient (Fig. 6). The analyses failed to show directional preferences as assumed by the hypotheses tested. Temperature and degree of cloud cover provided some information for predicting mean vector lengths and mean vanishing times, respectively. The surface wind component in the homeward direction was correlated with median homing performances.     

Pigeon homing: Different effects of olfactory deprivation in different countries

Summary 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.     

The development of sun compass orientation in young homing pigeons

Summary A series of clock-shift experiments with young homing pigeons of various ages was performed to determine at what age they normally learn sun compass orientation. The response of untrained pigeons to shifting of their internal clock seems to depend on their age. When the clock-shifted birds were tested at an age of 11 weeks and younger, their departure bearings did not differ significantly from those of controls (Fig. 1, diagrams on the right); in tests with birds 12 weeks and older the characteristic deviation indicating the use of the sun compass was observed (Figs. 2 and 3). Birds that had participated in a short training program, however, used the sun compass at 8 weeks, the earliest age tested (Fig. 1, diagrams on the left). These findings show that the time of development of the sun compass strongly depends on flying experience. Within the first months of a bird's life, it seems to take place after the bird has been confronted with the need to orient, either spontaneously during extended exercise flights around its loft or imposed by training releases.The departure bearings of the very young, inexperienced birds that did not rely on the sun compass, however, were already oriented homeward. This indicates that the ability to navigate develops independently of the sun compass, before the sun compass is learned.Dedicated to Prof. Dr. F.W. Merkel for his 70th birthday     

Do leaf-cutter ants Atta colombica obtain their magnetic sensors from soil?

How animals sense, process, and use magnetic information remains elusive. In insects, magnetic particles are candidates for a magnetic sensor. Recent studies suggest that the ant Pachycondyla marginata incorporates iron-containing particles from soil. We used leaf-cutter ants Atta colombica to test whether soil contact is necessary for developing a functional magnetic compass. A. colombica is the only invertebrate known to calculate a path-integrated home vector using a magnetic compass. Here, we show that A. colombica requires contact with soil to incorporate magnetic particles that can be used as a magnetic compass; yet, we also show that ants can biosynthesize magnetic particles. Workers from a soil-free colony ignored a 90° shift in the horizontal component of the geomagnetic field, yet oriented homeward despite the occlusion of any geocentric cues. In contrast, workers from a soil-exposed colony oriented to an intermediate direction between their true and subjective home in the shifted field. Homeward orientations under shifted fields suggest that ants calculated a path-integrated vector using proprioceptive information. Strikingly, ants from the soil-free colony also had magnetic particles; yet, as observed by ferromagnetic resonance, these particles differed from those in soil-exposed ants and were not associated with a magnetic compass sensitive to this experimental manipulation.     

Navigational strategies of homing pigeons at familiar sites: do landmarks reduce the deflections induced by clock-shifting?

To analyze the navigational strategy of homing pigeons at familiar sites in view of a possible role of local landmarks, two groups of pigeons—one familiar to the release site, the other unfamiliar—were released with their internal clock shifted 6 h fast, with untreated birds of both groups serving as controls. The two groups showed median deflections of 67% and 57%, respectively, of the expected size, with no consistent difference in the size of the deflection between familiar and unfamiliar birds. This clearly shows that familiarity with the release site and with the local landscape features does not affect the size of the deflections induced by clock-shifting. Obviously, pigeons familiar with the release site do not change their navigational strategy, but still continue to determine their home course solely as a compass course. General problems with orientation by landmarks are discussed; however, landmarks may help birds to recognize a site and recall the respective course.

---

Correct and false olfactory orientation of homing pigeons as depending on geographical relationships between release site and home site

Summary Pigeons from two German home sites were released at a site near Mantua in northern Italy. The home sites, Andechs and Würzburg, are 303 and 508 km north of the release site, respectively. Not only the initial bearings but still more the distributions of recoveries after a longer flight distance (median 65 km) were very different in pigeons from these two lofts. While the majority of the Wurzburg birds were found north of the release site, almost all birds from Andechs were found south of it (Fig. 1). Pigeons from both lofts, if made anosmic by sectioning the olfactory nerves, showed no average tendency towards change of latitude. These findings strongly suggest that both correct and false positional information were deduced by the birds from olfactory inputs. A coherent (though very hypothetical) interpretation of these and earlier results is based on regularly varying proportions of chemical tract compounds in the atmospheric boundary layer over the Alps and adjacent regions (Fig. 4).     

Orientation of the pied flycatcher Ficedula hypoleuca: cue-conflict experiments during spring migration

Hierarchical relationships among different compass systems in long-distance migrants are still a matter for discussion because different studies have led to highly variable and apparently contradictory results. We carried out cue-conflict experiments during spring migration on pied flycatchers Ficedula hypoleuca (Passeriformes, Muscicapidae). Birds were exposed to a conflict between celestial and magnetic information by altering the polarized light pattern or magnetic field. The polarization pattern was shifted (±90°) with filters, whereas the magnetic field was altered (+90°) through Helmholtz coils. Birds were tested in modified Emlen funnels both before and after the cue conflict; during the tests, only the natural magnetic field was available. This protocol was designed to test whether the experimental birds recalibrated their magnetic compass on the directional information derived from the light polarization pattern when the region near the horizon was visible during the conflict. Contrary to this expectation, we did not record any significant shift in magnetic orientation after one or repeated exposures to the cue conflict. Our results support earlier studies, which suggest that the magnetic field is the primary compass cue during the migratory period.     

Pigeon navigation: Charcoal filter removes relevant information from environmental air

Summary Homing pigeons were displaced and kept until they were released in airtight containers ventilated with environmental air that could be passed through: (a) a filter made of fiberglass paper retaining large portions of the solid and liquid aerosol particles, (b) an additional filter consisting of activated charcoal, or (c) no filter (controls). Before its release, each bird was taken out of the container, and its olfactory epithelium was immediately anesthetized by lidocaine (Xylocaine). Thus, neither experimentals nor controls were able to smell while their initial orientation behavior was being observed.The controls' initial bearings were better homeward-oriented than those of pigeons ventilated with charcoal-filtered air in 14 of 17 releases conducted in Italy and Germany, at distances of 24–155 km. In the final analysis, the bearings of the charcoal-filter birds did not show any relation to the direction toward home, whereas those of the controls did. Pigeons ventilated with air that had passed through only the paper filter did not behave noticeably differently from control pigeons.It is concluded that the material bases of olfactory navigation in pigeons are substances dispersed in the atmosphere, most probably in a molecular state.     

Spatio-temporal use of the urban habitat by feral pigeons (Columba livia )

Feral pigeons are descendants of wild rock pigeons that have adapted to the urban habitat. They have partially conserved the foraging behaviour of their wild ancestors (flights to agricultural areas) but have also developed new habits. Previous studies on the foraging strategies of feral pigeons have given various results, e.g. maximum distances reached by the pigeons (measured in a straight line from the resting places) differed between 0.3–0.5 km and 18–25 km. This study focuses on the spatio-temporal activity of feral pigeons in the urban habitat. We equipped 80 free-living feral pigeons from Basel, Switzerland with GPS receivers. We found three different foraging strategies for pigeons in Basel: (1) in the streets, squares and parks near the home loft, (2) in agricultural areas surrounding the city, (3) on docks and railway lines in harbours. The maximum distance reached by a pigeon was 5.29 km. More than 32% of the pigeons remained within 0.3 km of the home lofts and only 7.5% flew distances of more than 2 km. Females covered significantly longer distances than males, preferring to fly to more abundant and predictable food sources. Temporal activity patterns showed to be influenced by sex, breeding state and season. In contrast to wild rock pigeons and to feral pigeons in other cities, pigeons in Basel showed a clear bimodal activity pattern for breeding birds only. The differences between our results and those of other studies seem to be partly method-dependent, as the GPS-technique allows to record the pigeons’ localisations continuously in contrast to other methods. Other differences might be due to different kinds of food supply in the various cities. Our study shows that feral pigeons have individual foraging strategies and are flexible enough to adapt to different urban environments.Electronic supplementary material Supplementary material is available for this article at     

Magnetic compass mediates nocturnal homing by the alpine newt, Triturus alpestris

Experiments were carried out to investigate the use of magnetic compass cues in the nocturnal homing orientation of the alpine newt Triturus alpestris. Tests were carried out at a site 9 km to the east–northeast of the breeding pond. Newts were tested at night in an outdoor circular arena that provided an unimpeded view of celestial cues, in one of four symmetrical alignments of an earth-strength magnetic field. In tests carried out under partly cloudy skies newts exhibited homeward magnetic compass orientation. Because the moon was visible in some trials, but obscured by clouds in others, we investigated whether the presence of the moon contributed to the scatter in the distribution of magnetic bearings. When the moon was visible, the distribution of magnetic bearings was more scattered than when the moon was obscured by clouds, although in neither case was the distribution significant due, in part, to the small sample sizes. Moreover, when the moon was visible, newts oriented along a bimodal axis perpendicular to the moon azimuth, suggesting that the presence of the moon may have affected the newts behavior. To provide a more rigorous test of the role of magnetic compass cues when celestial cues were unavailable, nocturnal tests were carried out during the following migratory season under total overcast. In the absence of celestial compass cues, the distribution of magnetic bearings exhibited highly significant orientation in the homeward direction. These findings indicate that newts are able to orient in the homeward direction at night using the magnetic compass as the sole source of directional information. Moon light altered the newts behavior. However, this apparently resulted from the asymmetrical distribution of moon light in the testing arena, rather than the use of an alternative compass.     

Pigeon homing: the effect of a clock-shift is often smaller than predicted

This analysis is based on 103 releases with 6-h clock-shifted pigeons of various ages and experiences. Resetting the internal clock normally leads to a significant change in initial orientation; however, in half of the cases, the induced deflections are significantly smaller than predicted by the sun compass hypothesis. The relative size of the deflections decreases with increasing age and experience (Fig. 3). Only young pigeons with limited experience respond as expected, while old birds show deflections which are, on the average, only slightly more than half of the predicted size, except at extremely familiar sites (Table 2). There is no difference between fast and slow shifts (Fig. 4). It is not possible to clearly specify under what circumstances smaller deflections occur; previous clock-shifts (Fig. 5), familiarity with the release site (Table 4) and duration of the shifting procedure (Table 5) do not seem to be the reasons. Clock-shifting also tends to decrease the vector lengths and has a marked effect on homing performance (Table 7). Nevertheless, considerable numbers of clock-shifted birds return on the day of release before their internal clock has begun to be reset back to normal. The general role of the sun compass in bird orientation is considered and theoretical implications of our findings are discussed in view of the map and compass-model and the possibility that an alternative, non-time-compensating compass is used in parallel with the sun compass.     

Pigeon homing: sun compass use in the southern hemisphere

Although the sun compass of birds is based on learning the sun's arc during development, it was unclear whether birds can use the sun when its apparent movement is reversed, in particular, whether northern birds that have been introduced into the southern hemisphere can use the southern sun. To answer this question, clock-shift experiments were performed with local homing pigeons in Auckland, New Zealand (37°S). In three fast-shift tests and two slow-shift tests, the experimental birds showed deflections from the untreated controls that were the mirror images of those observed in the northern hemisphere. These results clearly show that homing pigeons in New Zealand use a sun compass that is adapted to the situation in the southern hemisphere. The learning processes establishing the compensation mechanisms thus appear to be free of constraints concerning the direction of the sun's movement. Differences from recent findings with migratory birds, where the direction of celestial rotation proved of crucial importance for establishing the migratory direction, are discussed: the differences may arise from the different orientation tasks, in particular, from the involvement of innate information in establishing the migratory direction. Received: 13 November 1997 / Accepted after revision: 28 February 1998     

Pigeon homing: new airbag experiments to assess the role of olfactory information for pigeon navigation

Summary In three series of experiments we assessed the effects of olfactory and non-olfactory information collected en route or at the release site on the initial orientation of homing pigeons. In the first experiment, pigeons were transported in open crates to two sites located in opposite directions from the home loft. They were left at the site for 1 h, then put into airtight containers filled with air from that site and brought back to the loft. From there, controls were transported back to the original site. Experimentals were transported to the opposite site. Upon arrival at the site, the olfactory mucosae of both groups were anesthetized with Gingicain. Thus in this experiment, control and experimental pigeons were exposed to different olfactory as well as to different non-olfactory information during displacement and at the site. In the second series, controls and experimentals were treated as in the first experiment, except that they were enclosed in the airtight containers at the very beginning of the experiment and were ventilated with synthetic air until arrival at the final release site. This treatment excluded the possibility to perceive olfactory information en route or at the site. In this series, the two groups differed only with respect to non-olfactory information perceived during displacement and/or at the release site. In the third series, we exposed pigeons at the loft to air collected either at the later release site (controls) or to air collected at a site located in opposite direction of the home loft (experimentals). Here the two groups differed only with respect to their exposure to air of different origin. In all three series, the pooled controls showed a directional preference that was statistically indistinguishable from the home direction. All three experimental groups were disoriented. In the first two series, the differences in the initial orientation of control and experimental pigeons were highly significant. In the third experiment, there was only very weak statistical evidence for a difference between controls and experimentals. These results suggest that more than one factor is involved in the pigeons' navigation system. According to the present experiment with synthetic air, pigeons probably gather and process non-olfactory information during the first part of their transport from the home loft to the release site. Thus, some kind of, in this case non-olfactory, route reversal seems to be involved in the homing process. In addition, the experiment involving only manipulations of airborne information indicated some olfactory component. Previous experiments at our loft did not result in disorientation of the pigeons if either only the access to airborne information had been removed or when otherwise unmanipulated pigeons had been transported in detours to the final release site. Therefore, we assume that our pigeons' navigation system relies on several cues. Deletion of one cue can be compensated by other information. Often the initial orientation of our pigeons is disturbed only when at least one cue is removed and another one provides false information.     

Can pigeons be fooled about the actual release site position by presenting them information from another site?

Summary The aim of the experiment was to test the hypothesis that pigeons depend on route- and/or site-specific airborne parameters to establish their position relative to the loft. Pigeons were transported to the release site with free access to the environmental air. They were then enclosed in large airtight containers filled with air from the release site and either transported via the loft to a release site in the opposite direction with respect to the loft (experimental birds) or via the loft back to the same site (control birds). Before release the pigeons (still inside the containers) were made anosmic by a local anesthetic applied to the olfactory membranes through the nostrils. Vanishing bearings of experimental birds were on the average in a direction opposite to home while the vanishing bearings of control birds were homeward oriented. For this initial orientation the pigeons seem to rely on airborne cues obtained at a site where they last had access to ambient air or cues obtained from the air inside the sealed containers. Irrespective of the treatment the bearings pooled with respect to north still show a residual orientation to the NE. There was no difference either in the homing speeds or in the homing times of anosmic control and experimental pigeons. We therefore have to assume further mechanisms guiding the pigeons home in addition to a possibly olfactory one.