Initial orientation of homing pigeons at the magnetic equator with and without sun compass

Summary 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.     

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     

Short-term residence in deflector lofts alters initial orientation of homing pigeons

Summary A modification of the deflector-loft technique first outlined by Baldaccini et al. (1975) is presented in which experienced homing pigeons that do not permanently reside in deflector lofts were housed in them for periods of 7–20 days. Upon release these birds consistently exhibited a deflection of mean vanishing bearings in the directions predicted by the olfactory hypothesis of pigeon homing. Two potential explanations for this short-term deflector-loft effect are suggested. One is that the olfactory map sense of homing pigeons is very flexible and capable of accurate readjustment in as short a period as seven days. Alternatively, it may be that nonolfactory cues are being altered by the deflector lofts in such a way as to result in behavior by pigeons that is consistent with the olfactory hypotheses. The short-term technique has the practical benefit of making it possible to conduct far more experiments in a single field season than was possible with the original deflector-loft method.     

Bird orientation: Single homing pigeons compared with small flocks

Summary The hypothesis that bird flocks orient more accurately than single individuals was tested on homing pigeons. Birds were released both singly and in flocks of three to six. Vanishing bearings were recorded and it was found that flocks were less scattered around the mean direction than singly released birds. Homing times were found to be shorter for flocks as compared to singles. This suggests that the average homing pigeon can gain in directional accuracy and save energy by joining other pigeons heading for the same goal.     

The effect of a “permanent” clock-shift on the orientation of experienced homing pigeons

Summary A group of experienced homing pigeons vas subjected to a 6 h slow shift of their internal clock and kept under these conditions for more than 2 months. During the overlap time between the natural and artificial photoperiods they were released for training flights to familiarize them with an area while living in a permanent shift.Tested outside the permanent shift training range, the experimentals always deviated about 30° clockwise from the mean of their controls, markedly less than in a regular 6 h slow shift. Inside the permanent shift training range, however, they oriented like the controls (Fig. 2). When their internal clock was returned to normal, the birds showed a larger counterclockwise deflection on their first flight, which was roughly comparable to the effect of a regular 6 h fast shift (Fig. 3). On later flights after normalization, this large shift was no longer found; instead we observed a roughly 30° counterclockwise deflection when they were released inside the permanent shift training range in the morning. This deflection did not seem to occur in the afternoon or outside the permanent shift training range (Figs. 4, 5), and it disappeared when the birds were repeatedly released from the same site (Fig. 6).The occurrence or non-occurrence of the deflection was independent of the duration of the shift or the time passed after normalization; it seemed to depend solely on whether the birds had become familiar with a given site in the situation of the permanent shift. This argues against an effect based on the sun compass. We tend to assume that the still unknown navigational map is involved. In this case, however, as the deflection is independent of the home direction and the type of release site bias, the factors in question would act very differently from the gradients on which the traditional concepts of the navigational map are based. The processes establishing and updating the map and their possible differences are discussed.Died on August 17, 1980     

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.     

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 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     

Calibration of the sun compass by sunset polarized light patterns in a migratory bird

Summary Migrating birds derive compass information from the sun, stars, geomagnetic field and polarized light, but relatively little is known about how these multiple sources of directional information are integrated into a functional orientation system. We found that migratory warblers exposed to a rotated polarized light pattern at sunset oriented at a constant angle to the axis of polarization. When polarized light cues were eliminated, this shifted orientation was maintained relative to the setting sun. Polarized light patterns, thus, appear to provide a calibration reference for the sun compass in nocturnal migrants, and may also play a role in calibrating other compass systems. Correspondence to: J.B. Phillips     

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     

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.     

Genetic determination and plasticity in the sun orientation of natural populations ofTalitrus saltator

As has been previously shown, talitrid crustaceans have an inherited compass which causes them to head in a direction appropriate to their original shoreline (even after several generations in the laboratory), while learnt components can improve the correctness of orientation in natural conditions. In order to extend this analysis to a greater range of populations and to show differences in the determination of direction finding behaviour, seven natural populations ofTalitrus saltator (Montagu) from differently oriented shores of the Ligurian (Marina di Vecchiano, Pisa), Tyrrhenian (Castiglione della Pescaia and Tombolo di Feniglia, Grossetto) and Adriatic (Casal Borsetti, Ravenna; Torre Fantine, Marina di Lesina and Lido di Siponta, Foggia). Italian coasts were compared for their rigidity-plasticity in sun orientation. The study was conducted from 1982 to 1985. Differences were given in relation to the dynamics of the shorelines, the stability of which changes over the years due to natural and artificial causes. Furthermore, in order to reveal something about the genetic determination of the compass, mass-crosses between geographically distant populations (Ligurian-Tyrrhenian on one side and Adriatic on the other) were performed, and the F1 and F2 inexpert offspring tested for sun orientation. The results show a partial or total disruption of the compass in cross offspring which is discussed in the light of oligogenic and polygenic transmission mechanisms.     

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.     

Detour experiments with homing pigeons: information obtained during the outward journey is included in the navigational process

Summary To test the hypothesis that information on the route of the outward journey is involved in the orientation of displaced homing pigeons, we compared the behavior of control pigeons that had been displaced by the most direct route with that of experimental pigeons that had been transported along detours to the same release sites. At distances of 40 km we found no consistent effect. At distances between 75 and 130 km, however, deviations to the left of the direct route induced deflections to the left, while deviations to the right induced deflections to the right, i.e. the deflections of the vanishing bearings tended to compensate for the initial detour of the outward journey. The deflections were smaller than the deviations of the routes; they were not related to the routes themselves or the location of the release sites. A significant correlation emerged with the vector length of the controls, as longer vectors were associated with smaller deflections. This suggests that information on the route of the outward journey is used together with local map information in the navigational process, the significance of the route-specific information apparently depending on quality and reliability of the available local information. The nature of factors controlling the detour effect is still open.Correspondence to: R. Wiltschko     

Magnetic compass orientation in the yellow-faced honeyeater,Lichenostomus chrysops,a day migrating bird from Australia

Summary In Australia, the southern populations of the yellow-faced honeyeater, Lichenostomus chrysops (Meliphagidae), perform annual migrations, with routes following the eastern coastline. In order to assess the role of magnetic cues in the migratory orientation of this diurnal migrant, its directional behaviour was recorded in recording cages under natural and experimentally manipulated magnetic-field conditions. During autumn the birds tested indoors in the local geomagnetic field showed a directional change from north initially to northwest later in the season (Fig. 1 a, b), which corresponds well with the general pattern of movement of this species in the field. Deflecting magnetic north to ESE resulted in a clockwise shift of the mean direction by 77° and 71°, respectively (Fig. 1 c, d), while no significant directional tendencies were observed in a magnetic field with a compensated horizontal component (Fig. 1 e, f; see Table 1). In outdoor tests in spring, the birds preferred southerly directions when tested in the local geo-magnetic field. In a magnetic field with a reversed vertical component (i.e. with an inclination pointing down instead of upwards) the birds reversed their directional tendencies and oriented northward (Fig. 2, Table 2). These results clearly show: (1) that yellow-faced honeyeaters can use the magnetic field for direction finding, and (2) that their magnetic compass functions as an inclination compass, as has been shown for several holarctic migrants.Correspondence to: W. Wiltschko