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First published online June 15, 2007
Journal of Experimental Biology 210, 2300-2310 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.004853
The magnetic compass of domestic chickens, Gallus gallus
1 FB Biowissenschaften, J. W. Goethe-Universität Frankfurt, D-61231
Frankfurt am Main, Germany
2 Centre for Neurosciences and Animal Behaviour, University of New England,
Armidale, NSW 2351, Australia
3 Department of Environmental Sciences, University of Technology Sydney,
Broadway, NSW 2007, Australia
4 Department of Physics and Astronomy, University of California, Irvine, CA
92697-4575, USA
* Author for correspondence (e-mail: wiltschko{at}bio.uni-frankfurt.de)
Accepted 16 April 2007
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Summary |
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Key words: directional training, magnetic compass, functional window, radical pair mechanism, Gallus gallus, domestic chicken
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Introduction |
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).
Migratory behaviour of robins has also been used to analyse the functional
properties of this compass mechanism, and two surprising characteristics have
become evident. Firstly, the robins' magnetic compass is an `inclination
compass', not based on the polarity of the magnetic field but rather on the
course of the field lines and their inclination in space
(Wiltschko, W. and Wiltschko,
1972). Secondly, the compass is closely attuned to the intensity
(field strength) of the local geomagnetic field, with a functional window that
can be adjusted to intensities outside the normal functional range
(Wiltschko, W., 1968;
Wiltschko, W., 1978;
Wiltschko, W. et al., 2006a).
Recent experiments have focused on the physical mechanisms underlying the
reception of magnetic compass information. The Radical Pair model
(Ritz et al., 2000) proposes
that the avian magnetic compass is based on radical pair processes in
specialized photopigments, with the first step leading to magnetoreception
being the absorption of a photon. This model allows two testable predictions,
namely (1) magnetoreception should be light dependent and (2) oscillating
fields in the MHz range that interfere with radical pair processes should
disrupt magnetoreception (Ritz et al.,
2000). Both predictions have been tested with European robins and
were found to be true. The avian magnetic compass requires light from the
short-wavelength part of the spectrum. Under 590 nm yellow light and beyond,
robins were disoriented (Wiltschko, W. and
Wiltschko, 1995; Wiltschko, W.
and Wiltschko, 1999; Muheim et
al., 2002). Using oscillating fields as a diagnostic tool, a
radical pair mechanism was identified as the primary process mediating
magnetic compass information (Ritz et al.,
2004; Thalau et al.,
2005; Wiltschko, R. et al.,
2005). Magnetite, found in birds in the ethmoid region and the
upper beak (e.g. Beason and Brennon,
1986; Hanzlick et al., 2000;
Fleissner et al., 2003;
Fleissner et al., 2007), on the
other hand, does not seem to be involved in the processes providing passerine
birds with compass information (e.g. Beason
and Semm, 1997; Munro et al.,
1997; Wiltschko, W. et al.,
2006b; Wiltschko, R. et al., 2007).
Meanwhile, a magnetic compass has been demonstrated in more than 20 species
of birds [see Wiltschko, R. and Wiltschko
(Wiltschko, R. and Wiltschko,
1995) for a summary
(Bäckman et al., 1997;
Gudmundsson and Sandberg,
2000)]. The vast majority are passerine migrants. The reason for
this bias towards migrating species appears to be based on the fact that,
during the migration season, orientation in the migratory direction is a very
reliable behaviour that provides an excellent tool for analysing the
underlying compass mechanism.
Until recently, the carrier pigeon, Columba livia, was the only
non-migratory avian species for which a magnetic compass had been
demonstrated; here, homing after displacement produced reliable directional
tendencies for analysis (Keeton,
1971). Conditioning experiments using magnetic stimuli, on the
other hand, have been largely unsuccessful, with the negative results by far
outnumbering the few positive ones (for a review, see
Wiltschko, R. and Wiltschko,
1995). The only successful operant studies involved detection of
changes in magnetic intensity and the presence or absence of a magnetic
anomaly rather than magnetic directions
(Bookman, 1977;
Mora et al., 2004;
Thalau et al., 2007).
Directional training has for a long time failed to elicit stable directional
tendencies in birds (e.g. Katz,
1978; Griffin,
1982; Alsop, 1987),
as birds do not easily respond to changes in the direction of the magnetic
field around them.
Recently, however, a magnetic compass has been demonstrated in domestic
chicken, Gallus gallus, using training to locate a model social
companion (Freire et al.,
2005); the young chickens were imprinted on a red ball, which was
then hidden behind one of four screens in each corner of a test apparatus. The
chicks were trained to locate the ball and to solve this spatial task by
remembering that it was always behind, for example, the screen in the North.
When the chicks were tested with North of the ambient magnetic field shifted
by 90° to the East, they shifted their search accordingly. This study was
the first to demonstrate magnetic compass orientation in an avian species by
conditioning.
In the present study, we follow up this initial work and, using the same
method as Freire et al. (Freire et al.,
2005), analyse the functional properties of the chickens' magnetic
compass and the nature of the physical processes underlying this
mechanism.
Materials and methods
The experiments were performed in Armidale, NSW, Australia during three
testing periods. The series analyzing the biological window of the chickens'
magnetic compass were begun in August 2005 and were completed in March 2006,
when the chickens were also tested for an effect of the local anesthetic
applied to their upper beak and for their response to monochromatic lights,
partly using the same chicks. The test series subjecting the chickens to
high-frequency fields was conducted in November 2005. Technical constraints
and time limitations resulted in differing numbers of chickens and differing
numbers of tests per chick in the various series.
All training and testing took place in a wooden building, where the local geomagnetic field of 55.9 µT, –62° inclination was undisturbed.
Test animals, imprinting and housing
We used brown-layer chicks from Nulkaba Hatchery, Cessnock, NSW, Australia.
The chicks were reared in isolation in cardboard pens (35x40x40 cm
high) from about 2 h after hatching. A red table-tennis ball (4 cm diameter)
was suspended on a string in the centre of the pen to provide the imprinting
stimulus. The chick adopted it as its `mother'; it was at ease in the presence
of the ball and would search for it when it was removed.
To encourage pecking and eating, the floor of the pen was lined with white
paper and sprinkled with chick starter crumbs that were periodically tapped
with a small round rod. Water was available ad libitum. On day 3,
wood shavings and an externally placed drinker were added to the pen. When the
chicks were about 4–5 days old, they were moved to a wooden building
where training and testing took place (for details, see
Freire et al., 2005).
Test arena, training and critical tests
The test protocol was identical to that used in previous experiments
demonstrating the chicken's ability to use the magnetic field for orientation
(Freire et al., 2005).
Test arena
The test arena consisted of a square white pen (80 cmx80 cm, 70 cm
high) with wood shavings on the floor. At each corner, corresponding to
magnetic North (mN), South (S), East (E) and West (W), were white screens (15
cm wide, 25 cm high) positioned perpendicularly to the diagonal, 15 cm from
the side walls of the arena. Diffuse `white' lighting was provided from above
by four incandescent light bulbs placed above the screens. This light reached
the birds after passing through a diffuser that formed the ceiling of the
arena [see fig. 1 in Freire et al. (Freire
et al., 2005)]. An overhead camera (Kobi DSP), placed above the
centre of the arena with the lens positioned through a 5 cm-diameter hole in
the ceiling, was used to observe the chick's behaviour on a monitor.
Care was taken to make the arena as uniform as possible. In order to minimize the impact of other cues that chicks could use for relocating the ball, the arena was rotated by 90°, 180° or 270° after each trial and test (see below), determined by a pseudorandom sequence. Additionally, the direction that the chick was facing when placed in the start cage and the side of the arena from which it was handled was also determined by a pseudorandom sequence.
Training phase
Chicks were trained to locate the red ball behind one of four screens, with
an equal number of chicks trained to North, South, East and West, the series
with the local anesthetic being an exception. A chick was placed in the centre
of the arena in a transparent plastic start cage (20x15 cm or
20x20 cm, 25 cm high) for 20 s next to the red ball that had served as
the imprinting stimulus. The ball was then slowly moved behind one screen; the
chick was released and allowed to search for it. This procedure was termed a
`visual displacement trial'. When the chick had moved behind the correct
screen and approached to within 5 cm of the ball, it was left there for 1 min
to stay with the ball (its social reward), then it was picked up and returned
to its home pen. Failure to approach the screen within 3 min led to
termination of that trial.
After successful completion of three visual displacement trials, the chick
was placed in the start cage with the ball already behind the screen; it was
then released and allowed to search for the ball. This was termed a
`relocation trial'. When the chick had moved behind the correct screen and
approached to within 5 cm of the ball, it was allowed to stay there for 1 min
and then returned to its home pen. If a chick failed to move behind the screen
within 3 min of release, it was reintroduced into the start cage and received
a visual displacement trial before being returned to its home pen. In order to
take the axiality of the responses (see
Freire et al., 2005) into
account, a second identical ball was placed behind the screen directly
opposite the screen concealing the first ball but only after a chick had
chosen this screen twice in subsequent relocation trials. The reason for
adopting this procedure was to provide a reward in order to prevent extinction
of the response.
Each chick continued to receive relocation trials until it reached `criterion', which was defined as moving behind the screen and approaching to within 5 cm of the ball in less than 20 s of release on three consecutive relocation trials. Trials in which a chick moved behind other screens not concealing a ball prior to locating the ball were scored as incorrect.
All training, i.e. visual displacement trials and relocation trials, took place under `white' light in the local geomagnetic field.
Testing
The critical tests were performed when the chickens were between 12 and 22
days old. The procedure was similar to that used in the relocation trials,
except for two aspects: (1) these tests were unrewarded, i.e. there was no
ball behind the correct or the opposite screen, and (2) magnetic North was
shifted to the East (see below). That is, the chicks never got to see the red
ball in a field with magnetic North shifted.
These tests were interspersed with relocation trials in the local geomagnetic field with the red ball present in order not to discourage the chicks. After a test, the chick with the ball was returned to the home pen for a few minutes before being placed into the start cage and presented with a relocation trial. When a chick moved behind the screen and approached the ball in less than 20 s of release without prior walking behind other screens, it was allowed to remain in the arena for a further minute with the ball as a reward. After this, it was returned to the home pen before it was presented with the next test. If the chick failed to approach the ball within 3 min of release in the relocation trial, it received another visual displacement trial and then returned to the home pen. After the next successful relocation trial, it was again presented with a critical test.
Each chick received an equal number of tests in each of the test conditions to which it was assigned (see below). The order of presentation of these test conditions was randomized in the series testing for the biological window and for the effect of the high-frequency fields. The series under monochromatic light and those with local anesthesia of the upper beak took place at the end of an individual chick's testing period and involved some chicks that had already been tested in one of the series determining the biological window; in these cases, the respective control tests also served as control tests for these series. The blue and red lights were presented in pseudorandom order; the tests using the local anesthetic were performed one after the other (see below).
Experimental conditions
The experimental conditions involved experimentally altered magnetic fields
that were presented to the chicks only during testing. The various test fields
were produced by pairs of Helmholtz coils (2 m diameter, 1 m clearance) with
30 windings of copper wire on each side. When testing for the functional
window and for the effect of the local anesthetic, we used three pairs of
coils with their axes aligned horizontally in the North–South direction,
horizontally in the East–West direction and vertically. These coils
could be operated independently to modify each component of the magnetic field
separately. For the tests for the effect of high-frequency fields and the
effect of the wavelength of light, we used one pair of coils with its
horizontal axis aligned 135–315°, which allowed us to turn magnetic
North by 90° clockwise to the East without altering inclination and
intensity.
All critical tests took place in experimental magnetic fields with North turned by 90° to the East with the inclination unchanged (mN=E, –62° inclination), to ensure that the chicks were relying on the ambient magnetic field for locating the imprinting stimulus. This field with the intensity equivalent to that of the local geomagnetic field (55.9 µT) served as the control condition and provided the reference for assessing the performance in the other test conditions. The other conditions varied according to the experimental series.
Testing for a functional window
For analyzing the functional window, the chicks were additionally tested in
magnetic fields with different intensities but with the same direction and
inclination as the control field. In the first part of the series, these
fields were 50% weaker and stronger than the local geomagnetic field, with
total intensities of 27.9 µT and 83.8 µT, respectively. In the second
part of the series, the intensity differences were 25%, with the respective
intensities being 41.9 µT and 69.9 µT.
Monochromatic lights
To test for wavelength dependence of the chickens' magnetic compass, the
chicks were tested in the same magnetic field as in the control condition
under monochromatic blue and red light, with the tests under `white' light
serving as controls. The test lights were produced by four sets of bright
light-emitting diodes (LEDs) mounted above the screens so that the light
passed through a diffuser that formed the ceiling of the test arena. The blue
diodes had a peak wavelength of 465 nm and a bandwidth of 50% intensity
between 454 and 476 nm; the red diodes had a peak wavelength of 645 nm and a
bandwidth of 625–666 nm. The monochromatic lights were of about equal
quantal flux, with the intensity of blue light in the arena being 0.60 W
m–2 and that of red light being 0.45 W
m–2.
Effect of high-frequency fields
In this test series, the chicks were subjected to a high-frequency field of
1.566 MHz. This oscillating field was produced by a coil antenna consisting of
a single winding of coaxial cable with 2 cm of the screening removed. The
antenna was mounted on a horizontal wooden frame surrounding the test
apparatus and was fed by oscillating currents from a high-frequency generator
(for details, see Ritz et al.,
2004). This way, the high-frequency field was presented
vertically, forming a 28° angle to the static magnetic vector. The
high-frequency field was presented at two intensities: 480 nT, which is a
little less than 1% of that of the geomagnetic field, and 48 nT, one tenth of
the preceding one.
Effect of local anesthesia of the upper beak
Chicks were tested in the control field with the skin of their upper beak
anesthetized with the local anesthetic xylocaine® (active substance:
lignocaine hydrochloride 2%; produced by AstraZeneca, North Ryde, NSW,
Australia). It was applied externally by gently rubbing a cotton bud soaked
with the anesthetic along the edges of the upper beak. After waiting for about
10 min for the effect to set in, testing began. In this test series, the
procedure was adjusted to the lasting effect of the anesthetic: the control
tests were done first, followed by the tests with the anesthetic applied. The
latter were conducted in sequence without relocation tests, and the anesthetic
was reapplied after the third test.
Data analysis and statistics
In each test series, eight or 12 chicks were tested five or 10 times in
each test condition. As before (Freire et
al., 2005), the chickens' choices were axial, focusing on the
correct screen and the screen directly opposite. The null hypothesis thus
predicts about 50% choices on the correct axis and 50% on the axis
perpendicular to it. We determined the percentage of choices on the correct
axis for each bird and calculated the mean ± standard deviation for
each series. The sign test was used to test whether or not there were more
choices on the correct axis than chance level, with significance indicating
that the chicks were oriented along this axis in the respective test
condition.
The proportion of correct choices was then arcsine transformed
[p'=arcsin(
p)x57.298], as described by
Zar (Zar, 1999), and analyzed
in a repeated-measures analysis of variance (ANOVA). The F-test was
used to look for differences between the various test conditions.
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Testing for a functional window
In these series, two groups of chickens were tested in the control field
(with the intensity of the local geomagnetic field) and in fields with the
intensity 50% or 25% weaker and stronger. In all these fields, magnetic North
was shifted by 90° to the East. Table
1 summarizes the percentage of correct choices and the number of
chickens performing above average in the different experimental conditions;
Table A1 in the Appendix gives
the individual chicken's choices.
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In the series varying magnetic intensity by 50%, the birds chose the screen in the correct magnetic direction or the screen directly opposite it in 78% of the tests in the control field, with each of the 12 individual chicks being above chance level (Sign test, P<0.001; see Table 1). In the weaker and stronger fields, only 47% and 42% of the choices, respectively, were on the correct axis, with the choices in these two conditions not different from chance level (see Table 1). The difference between the performances in the three test conditions is significant (ANOVA, F2,22=24.97, P<0.001), with significantly more choices of the correct axis in the control field than in the weaker or stronger fields (see Table 1). That is, the chickens showed significantly oriented search behaviour in the test field with intensity like the local geomagnetic field but were not oriented in the two other fields (Fig. 1, top row).
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These data demonstrate that the chickens' magnetic compass is restricted to a functional window, working only at total intensities equal or similar to that of the local geomagnetic field, with a decrease as well as an increase in magnetic intensity leading to disorientation. Interestingly, the functional window appears to be asymmetric with respect to the ambient geomagnetic field: its lower limit lay between 25 and 50% below the local field's intensity of 55.4 µT, whereas the upper limit was less than 25% above this intensity.
Testing for the physical principle underlying the chickens' magnetic compass
The Radical Pair model (Ritz et al.,
2000) predicted that magnetoreception would be light dependent and
can be disrupted by high-frequency fields in the MHz range (for details, see
Ritz et al., 2000;
Ritz et al., 2004). In view of
this, we tested the chickens under monochromatic blue and red light and
subjected them to oscillating magnetic fields, a diagnostic tool for radical
pair processes. Another potential mechanism of magnetoreception involves
iron-based receptors (e.g. Kirschvink and
Gould, 1981; Davila et al.,
2003), and such receptors have been described in the upper beak of
pigeons (Fleissner et al.,
2003; Fleissner et al.,
2007). Chickens have a similar arrangement of receptors in their
upper beak (Fleissner et al.,
2007); hence we also tested chicks whose upper beak was locally
anesthetized in order to temporarily disable these receptors.
Testing for an effect of the wavelengths of light
For technical reasons, this test series had to be performed at the end of
testing and could not be completed. Only six chickens were tested under
monochromatic light and the distribution of their choices is given in
Fig. 2, top row. Under white
light and monochromatic 465 nm blue light, 73% of their choices were on the
correct axis; under 645 nm red light, only 50% of the choices were correct,
suggesting oriented behaviour under white and blue but not under red light.
However, due to the small sample size of only six chicks, neither of the
distributions differed from random (see
Table 2), and they did not
differ from each other (ANOVA, F2,10=1.811,
P=0.213). However, it should be noted that under white and blue
light, five chicks performed above chance level, whereas only two chicks did
so under red light (Table
2).
Testing for an effect of oscillating fields in the MHz range
Adding oscillating fields to the local geomagnetic field caused random
searching (Fig. 2, middle row).
While the chickens performed 66% of choices on the correct axis in the control
field, with five of the eight birds performing above and three at chance
level, the percentage of correct choices was only 50% in the 480 nT
oscillating field. Even in the markedly weaker oscillating field of only 48
nT, the percentage of correct choices was only 46%, reflecting searches that
were no longer oriented (Table
2). The difference between the three groups is significant (ANOVA,
F2,14=7.144, P=0.007), with significantly more
choices on the correct axis in the control field than in the two oscillating
fields (F-test, P=0.015 and P=0.003, respectively).
The disorienting effect of the oscillating fields indicates a disruption of
the reception processes, thus identifying an underlying radical pair
mechanism.
Testing for an effect of local anesthesia of the upper beak
Anesthesia of the upper beak did not affect the chicken's searching
behaviour (Fig. 2, bottom row):
78% and 75% of the choices were on the correct axis, and all chickens
performed above chance level, untreated as well as with the beak anesthetized
(Table 2). There was no
difference between the two test conditions (F1,7=0.030,
P=0.867). These findings speak against an involvement of iron-based
receptors in the upper beak in providing the magnetic compass information the
chicks rely on when searching for the correct screen.
The performance of the individual chicks in these three test series is given in Tables A2, A3, A4 in the Appendix.
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Table 2 also includes the latencies, i.e. the time required to score in the various experimental conditions. They vary greatly and indicate a surprising phenomenon: while there is no general difference between conditions where the chicken can orient and those where they cannot in the tests documenting the biological window and those with oscillating field, there are treatments that affect the latencies but not the directional choices. This is true for the local anesthesia: while the chickens show a preference of the correct axis with and without treatment, they need significantly longer to choose when their upper beak is anesthetized (F1,7=6.631, P=0.037). These longer latencies may be attributed to possible general discomfort of having a sensory input disrupted, even if it is not the one used for locating direction. The latencies also differ significantly under the different coloured lights (ANOVA, F2,10=14.504, P<0.001). Here, the chicks take significantly longer under red light, where they appear to be disoriented, than under white and blue light (F1,7=28.366, P=0.0003 and F1,7=11.314, P=0.0072, respectively). It seems likely that the sudden exposure to a monochromatic environment may confuse the chicks, with red having a stronger effect than blue because it additionally interferes with their ability to solve the task.
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The chickens' magnetic compass, like that of robins, works in a rather
narrow functional window closely attuned to the intensity of the local
magnetic field. For robins living in a local field of 
46 µT, the upper
limit lies between 54 µT and 60 µT, while the lower limit lies between
43 µT and 34 µT; i.e. between an increase of 17–30% and a decrease
of 7–26% (Wiltschko,
1978). It is not necessarily asymmetrical, as appears to be the
case in the chickens, but without a systematic study we cannot tell whether
the functional windows of the two species are truly different – the few
intensity levels tested so far do not allow a meaningful conclusion.
The data in the other test series indicate that the same physical
principles underlie the compass mechanism of both robins and chickens. The
data obtained under monochromatic blue and red light from only six chicks do
not allow a definite answer about a wavelength dependence of the chickens'
magnetic compass. The average percentage of correct choices under the various
light conditions, however, is in agreement with a wavelength dependence as
found in European robins (Wiltschko, W.
and Wiltschko, 1995;
Wiltschko, W. and Wiltschko,
1999) and two other species of passerines, the Australian
silvereye, Zosterops lateralis
(Wiltschko, W. et al., 1993),
and the European garden warbler, Sylvia borin
(Rappl et al., 2000). The
chickens' response to the high-frequency field of 1.566 MHz, on the other
hand, identifies their magnetic compass as a mechanism based on radical pair
processes like that of robins (Ritz et
al., 2004; Thalau et al.,
2005; Wiltschko, W. et al.,
2005). Here, the great sensitivity of the chickens is remarkable:
an oscillating field of only 48 nT, i.e. less than 1/1000 of the local field's
intensity, already disrupted oriented searching. The frequency used in this
study, 1.566 MHz, represents the Larmor frequency in the local magnetic field
of 55.9 µT. A particularly sensitive resonance at the Larmor frequency
indicates specific properties of the crucial radical pair (T.R. et al.,
manuscript in preparation). Robins also respond very sensitively to an
oscillating field with the local Larmor frequency (T. Ritz, R. Wiltschko and
P. Hore, manuscript in preparation), and this suggests an identical mechanism,
with the same receptor molecule forming the radical pair in both species.
The non-involvement of the iron-based receptors in the upper beak is likewise a parallel to the magnetic compass of robins. Robins, too, remained well oriented with these receptors deactivated by local anesthesia and continued to prefer their migratory direction as when they were untreated. With robins, there is also evidence that applying the anesthetic in the way that it was applied in the present study can affect other responses, e.g. `fixed direction' responses, but it does not interfere with their inclination compass (Wiltschko, R. et al., 2007).
There is no direct evidence that the chickens' compass is also an
inclination compass. The response of chicks was axial rather than unimodal
– they preferred the correct screen and the one opposite to it, e.g. the
ones in the North and the South over those in the East and the West (see
Freire et al., 2005). Hence,
reversing the vertical component – the diagnostic test for an
inclination compass – could not be applied, because in case of axiality,
a reversal in orientation does not become evident. Theoretical considerations,
however, clearly indicate an inclination compass: the underlying mechanism was
identified as a radical pair mechanism, and radical pair processes are not
sensitive to polarity but respond only to the course of the field lines. The
observed axially bimodal responses suggest that the chickens, in contrast to
the robins, did not distinguish the two ends of the axis.
In summary, our analysis of the chickens' magnetic compass and comparison
with the magnetic compass of robins points to an identical mechanism, namely a
light-dependent inclination compass based on radical pair processes that works
in a narrow functional window attuned to the local geomagnetic field. The same
appears to be true for the magnetic compass of pigeons: it is also an
inclination compass (Walcott and Green,
1974; Visalberghi and Alleva, 1978), probably with a similar light
dependence as in robins (Wiltschko, R. and
Wiltschko, 1998). This seems to suggest that it may be a mechanism
common to all birds. Passerines and pigeons on the one hand and chickens on
the other hand are not closely related. The galliformes belong to an ancient
line of birds, which separated from the more modern lines of birds as early as
the Cretaceous period (Cooper and Penny,
1997). Hence, the existence of the same type of magnetic compass
mechanism in birds of both lineages implies that this type of compass is of
great age and probably was already developed in the common ancestors of all
modern birds.
The above considerations, together with the finding that the avian magnetic
compass is well developed in a sedentary species such as the domestic chicken,
indicate the ecological background of its development. In contrast to what is
frequently stated, it has not been developed in connection with extended
migrations. It must be assumed that it already existed before modern birds
began to migrate. When some species began with seasonal movements, the
existence of an efficient compass mechanism may have facilitated migration
over extended distances. Originally, the magnetic compass developed most
likely as a mechanism for orientation within the home range, to allow the
birds fast and efficient movements between roosts, nest, feeding places,
water, etc. – a function that it still serves today in non-migrants and
in migrants outside migration. The finding that even domestic chickens, after
thousands of years of domestication
(Fumihito et al., 1996), still
have a well-developed magnetic compass highlights the important role of this
mechanism in birds' everyday navigation tasks.
Appendix: tables giving the directional choices of the chicks
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Acknowledgments |
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References |
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TOPSummaryIntroductionResultsDiscussionReferences |
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