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     

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.     

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.     

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.     

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 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     

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.     

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).     

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.     

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     

The role of daytime cues in the development of magnetic orientation in a night-migrating bird

To assess the role of celestial rotation during daytime in the development of the magnetic compass course, pied flycatchers (Ficedula hypoleuca Pallas, Muscicapidae) were handraised in Latvia under various celestial and magnetic conditions. Tests were performed during autumn migration in the local geomagnetic field (50 000 nT, 73° inclination) in the absence of celestial cues. A group of birds that had never seen the sky showed a bimodal preference for the migratory southwest-northeast axis, whereas a second group that had been exposed to the natural sky from sunrise to sunset in the local geomagnetic field showed a unimodal preference for the seasonally appropriate southwesterly direction. A third group that had also been exposed to the daytime sky, but in the absence of magnetic compass information, also oriented bimodally along a southwest-northeast axis. These findings demonstrate that observing celestial rotation during daytime enables birds to choose the right end of the migratory axis for autumn migration at the Latvian test location. This transformation of axial behavior into appropriate migratory orientation, however, requires the birds to have simultaneous access to information on both celestial rotation and the geomagnetic field. Received: 19 September 1997 / Accepted after revision: 22 November 1997     

Night sky orientation of migratory pied flycatchers raised in different magnetic fields

Summary To test whether the initial night sky orientation response of migratory pied flycatchers (Ficedula hypoleuca) is calibrated from the ambient magnetic field experienced by birds during their first summer, three groups of pied flycatchers were hand-reared and then held under different magnetic field conditions during the course of the summer. All groups were held outdoors and given full exposure to the day and night sky. One group was exposed to the local earth's magnetic field. A second group was exposed to a magnetic field of local earth strength, local earth inclination shifted 105° counter-clockwise relative to the local earth's field. The last group was exposed to a vertical, and thus nondirectional magnetic field.In autumn, the birds were tested for their orientation under the night sky in the absence of a directional magnetic field. When tested, all three groups were oriented with mean directions varying from south to southeast. No statistical differences emerged in any between group comparisons. The data indicate that earth's magnetism does not serve as a calibrating reference in the development of a pied flycatcher's initial orientation response to the night sky.     

Variation in zonal recovery in four Talitrus saltator populations from different coastlines: a comparison of orientation in the field and in an experimental arena

Under stressful conditions (e.g. finding themselves on dry or moisture-saturated substrates) littoral talitrids (Crustacea, Amphipoda) demonstrate zonal orientation, in which they must promptly reach the optimal zone of the beach, the wet fringe near the shoreline. A relationship might therefore exist between the use of orientation and the frequency of such stressful conditions in the natural environment. Moreover, the efficiency of orientation toward the sea could be related to the possibility of using strategies other than zonal orientation in order to avoid stress. This study analysed the actual use and efficiency of orientation under natural conditions of four Talitrus saltator (Montagu, 1808) populations from Mediterranean and northern European Atlantic coasts with different ecological features. Orientation tests were carried out on the beach with all natural cues available. Then the same individuals underwent control experiments to study their sun orientation far from the sea in an experimental arena. The following results emerge from the comparison of the circular distributions: (1) marked differences among populations in the precision of zonal recovery under natural conditions; (2) a common solar orientation capacity in the control tests far from the sea; (3) different orientation choices of the same individuals according to the test conditions, natural or controlled. The habitat diversity of the four populations (amount, distribution and kind of detritus and wrack on the beach, degree of coastal erosion, orientation of the shoreline, human use of the beach) provides an ecological interpretation for the differences in orientation observed among populations. Received: 13 October 1997 / Accepted after revision: 26 April 1998     

Essential fatty acid (docosahexaenoic acid, DHA) availability affects growth of larval herring in the field

Larval fish growth and survival depends not only on prey quantity, but also on prey quality. To investigate effects of prey fatty acid concentration on larval herring growth, we collected different prey organisms and larval herring (Clupea harengus L.) in the Kiel Canal during the spring season of 2009. Along with biotic background data, we analysed fatty acids both in prey organisms and in the larvae and used biochemically derived growth rates of the larvae as the response variable. Larval herring reached their highest RNA/DNA derived growth rates only at high docosahexaenoic acid (DHA) concentration. When the ratio of copepodids to lesser quality cirriped nauplii was low, larval growth and larval DHA concentration were both significantly negatively affected. This was true even as prey abundance was increasing. This finding indicates that even in mixed, natural feeding conditions, growth variations are associated with DHA availability in larval fish.