Pigeon Homing: Observations, Experiments and Confusions

Abstract

Homing pigeons can return from distant, unfamiliar release points. Experienced pigeons can do so even if they are transported anesthetized and deprived of outward journey information. Airplane tracking has shown that they make relatively straight tracks on their homeward journey; therefore, pigeons must have some way of determining the home direction at the release site. Manipulating the pigeon's internal clock causes predictable deviations in their flight direction relative to home. When the sun is not visible, such clock shifts have no effect. This result implies a two-step system: the determination of the home direction and the use of a sun compass to fly in that direction. When pigeons cannot see the sun they use a magnetic compass. The use of compass cues to select and maintain a direction of flight is well understood compared with the uncertainty surrounding the nature of the cues used to determine the home direction when pigeons are released at an unfamiliar site. Because they generally home successfully from any direction and distance from the loft, without requiring information gathered on the outward journey, it seems likely that they use some form of coordinate system. Presumably, a displaced pigeon compares the values of some factor at the release site with its remembered value at the home loft. This factor might be olfactory, it might be some feature of the earth's magnetic field or it might be something else. There is some evidence that pigeons may use several cues and that pigeons raised in different lofts under different environmental conditions may prefer to use one cue over another. I believe that it is this flexible use of multiple cues that has led to so much confusion in experiments on pigeon homing.

Full text

Homing pigeons released at unfamiliar locations return to
their home lofts in most cases. This phenomenon is the basis
for a substantial world-wide sport. In the United States, the
longest pigeon races involve flights of 1800km and, because
substantial financial rewards accrue to the owner of the fastest
pigeon, there is severe selection for those pigeons that home
the fastest. Many investigators have used these birds as a model
of animal navigation. From an evolutionary point of view, our
modern homing pigeons have presumably descended from the
wild Mediterranean rock doves. These birds nested on cliffs
and foraged for food in nearby fields. Homing probably
evolved in the context of returning to the nest site with food
for the young. In many ways, a displaced homing pigeon faces
a more difficult task than a migratory bird; it has no control
and usually little information on the distance or direction of its
experimental displacement. Yet, in almost every case, the
pigeon finds its way home.
This ability to return home from unfamiliar locations raises
the question of what sensory cues pigeons use both to
determine the direction towards home and to maintain their
flight in that direction. These are two quite distinct processes.
In the first, a pigeon must determine the direction to fly in order
to reach home. Because, in human terms, this task is something
we accomplish by using a map or chart, this position-finding
step is often called the ‘map’. The term ‘map’ has unfortunate
connotations. It suggests that the pigeon has a spatial
representation of the environment. Actually, all the pigeon
needs is a direction towards the home loft. Once a direction to
fly has been decided upon, a pigeon might use some other cue
as a compass to keep on course (Kramer, 1953).
Pigeons can home under a wide variety of conditions. They
fly when the sun is visible and when it is not. With training,
they will even fly at night. They fly with both head and tail
winds, but they land in heavy rain. Indeed, what is remarkable
about their homing success is that only a few experimental
manipulations, such as anosmia and release at certain locations,
prevent a pigeon from reaching home.
Young pigeons seem to make use of information obtained
on the outward journey in order to return home (Wiltschko and
Wiltschko, 1978). Older pigeons transported to the release site
inside sealed metal containers, supplied with bottled air,
anesthetized and placed on rotating turntables, all of which
should make it hard for them to keep track of their outward
journey, still home (Wallraff, 1980; Wallraff et al. 1980). This
ability implies that these pigeons are able to determine the
direction towards home without using information obtained on
21
The Journal of Experimental Biology 199, 21–27 (1996)
Printed in Great Britain © The Company of Biologists Limited 1996
JEB0067
Homing pigeons can return from distant, unfamiliar
release points. Experienced pigeons can do so even if they
are transported anesthetized and deprived of outward
journey information. Airplane tracking has shown that
they make relatively straight tracks on their homeward
journey; therefore, pigeons must have some way of
determining the home direction at the release site.
Manipulating the pigeon’s internal clock causes
predictable deviations in their flight direction relative to
home. When the sun is not visible, such clock shifts have
no effect. This result implies a two-step system: the
determination of the home direction and the use of a sun
compass to fly in that direction. When pigeons cannot see
the sun they use a magnetic compass. The use of compass
cues to select and maintain a direction of flight is well
understood compared with the uncertainty surrounding
the nature of the cues used to determine the home direction
when pigeons are released at an unfamiliar site. Because
they generally home successfully from any direction and
distance from the loft, without requiring information
gathered on the outward journey, it seems likely that they
use some form of coordinate system. Presumably, a
displaced pigeon compares the values of some factor at the
release site with its remembered value at the home loft.
This factor might be olfactory, it might be some feature of
the earth’s magnetic field or it might be something else.
There is some evidence that pigeons may use several cues
and that pigeons raised in different lofts under different
environmental conditions may prefer to use one cue over
another. I believe that it is this flexible use of multiple cues
that has led to so much confusion in experiments on pigeon
homing.
Key words: navigation, orientation, homing, pigeon, Columba livia,
sun compass, magnetic field, olfaction.
Summary
PIGEON HOMING: OBSERVATIONS, EXPERIMENTS AND CONFUSIONS
CHARLES WALCOTT
Laboratory of Ornithology and Section of Neurobiology and Behavior, Cornell University, Ithaca, NY 14850, USA
Introduction

22
the outward journey. Since, in contrast to honeybees, pigeons
can orient towards home whatever the direction and distance
(within 1800km or so from home) from which they are
released, it must be concluded that they can truly ‘navigate’,
i.e. they are able to determine the direction of the home loft
from any release point.
Adopting a home loft
Pigeons seem to adopt a home loft at about 6 weeks of age.
Before that time, a pigeon will adopt any loft as home; after
that, it becomes difficult to train birds to a new loft location.
There are reports that the Army Pigeon Corps had a way of
training pigeons to constantly changing loft locations, but this
was clearly a difficult and laborious procedure (War
Department, 1921, 1945). Once a loft location is adopted as
home, it seems to last throughout a pigeon’s life. I have had
birds return to their original loft at Harvard University after
being held prisoners in the Lincoln, Massachusetts, loft for 7
years! The process of getting young birds to adopt a new loft
seems to be hastened and made more effective by allowing
them to fly around the loft, but this activity is not absolutely
required. Birds reared in a loft with no external experience can
still home, albeit slowly and with poor success (Wallraff,
1979).
Pigeon tracking
One of the most direct approaches to understanding pigeon
homing is to follow the birds on their trip home. Hitchcock
(1952, 1955) and Griffin (1952) followed flocks visually in an
airplane. Talkington (1967) and Graue (1963, 1965) used
helicopters, as did Fiaschi et al. (1981). Michener and Walcott
(1967) followed radio-tagged pigeon in airplanes, and recently
Bramanti et al. (1988) put individual flight recorders on the
backs of pigeons homing in Italy. All the tracks from these
experiments show that unmanipulated pigeons fly on relatively
straight paths to the home loft. Taken together, the tracks
suggest that a displaced pigeon has a clear idea about the
direction to its home loft at the outset. And it is this outset
orientation that is captured by the ‘vanishing direction’, the
direction in which a pigeon disappears from the view of an
observer with binoculars at the release site.
Release site biases
If one looks at the vanishing directions of large groups of
pigeons at different sites, rarely do all pigeons choose the same
direction; there is scatter in the pigeon’s choices. Furthermore,
there are differences related to the particular release site which
Keeton (1973) called ‘release site biases’. As Fig. 1 shows,
Cornell pigeons provide several dramatic examples: at Castor
Hill, North of Ithaca, the vanishing bearings of Cornell pigeons
tend to be deflected to the west. Yet pigeons home normally
from the site. At Jersey Hill, 132km west of Ithaca, Cornell
pigeons are disoriented and homing performance is very poor.
Releasing pigeons raised in different loft locations at both of
these sites shows that their behavior differs between these sites.
These results, together with those of Schmidt-Koenig (1963)
and many others, indicate that a pigeon’s orientation is a
function both of its home loft location and of the release site.
Cues used in homing
Pigeons equipped with frosted lenses depriving them of
visual landmarks still orient; some even find the loft (Schlichte
and Schmidt-Koenig, 1971; Schmidt-Koenig and Walcott,
1978). Clearly, detailed visual information is not essential for
navigation. The same is true for birds whose cochleas have
been destroyed; orientation was not affected (G. A. Manley,
personal commmunication). Appearently, acoustic information
is not required either.
Clock-shifts, in which a bird’s internal sense of time is
altered, do have an effect under sunny conditions. A pigeon
with a 6h clock-shift makes on average a 90˚ error in its
homeward vanishing bearing; the direction of the error depends
upon the direction of the shift (Schmidt-Koenig, 1960, 1990;
Schmidt-Koenig et al. 1991). This error occurs even at very
short distances from the lofts, although familiar landmarks are
presumably visible (Graue, 1963; Alexander, 1975). It also
occurs at both familiar and unfamiliar release points (Fuller et
al. 1983). Somewhat surprisingly, the exact amount of the error
may vary depending on the release point used. There are places
around Ithaca, NY, where a 6h clock-shift results in errors of
from less than 40˚ to more than 110˚ in the pigeon’s vanishing
bearings. Many birds with a 6h clock-shift never home. Birds
with smaller clock-shifts exhibit smaller errors and better
homing success. Most pigeon researchers report similar results.
Keeton (1969) reported that his 6h clock-shifted pigeons,
released under overcast skies, were well oriented towards home.
This success implies that the pigeons were not able to see the
sun through the clouds and that, furthermore, the sight of the
sun was not essential for successful orientation and homing.
Keeton reasoned that if his pigeons were well oriented under
overcast they must be using a cue other than the sun compass.
He found that pigeons with magnets fastened on their backs
were often disoriented when released under overcast (Keeton,
1971; Ioalè, 1984). This effect was very conspicuous at one
particular release site (Campbell, NY), but it was much weaker
at other release sites. Pigeons equipped with a pair of coils
generating a magnetic field of the strength of the Earth’s natural
magnetic field around their heads had slightly deflected
vanishing bearings under sun. Although the effect was only
10–20˚ and statistically not significant for any one release, it
was consistent (Walcott, 1977). When the sun was not visible,
birds wearing coils with one magnetic polarity (SUP; the south-
seeking needle of a compass placed between the coils pointing
up, towards the pigeon’s head coil) vanished towards home,
whereas birds with coils of the opposite polarity (NUP)
vanished in the opposite direction (Walcott and Green, 1974;
Visalberghi and Alleva, 1979). The behavior of a pigeon
wearing a set of head coils depends dramatically on the
C. WALCOTT

23Pigeon homing: sensory cues
visibility of the sun. Under a sunny sky, the coils, whatever their
polarity, only deflect the pigeon’s vanishing bearings by a few
degrees. If a pigeon wearing an NUP coil starts its homeward
journey under overcast, it will head away from the release point
in the direction away from home. Should the sun appear, even
if only momentarily, through a hole in the clouds, it will reverse
course and head directly for home. Whereas the behavior of
birds with magnets seems to depend somewhat upon where they
are released, the vanishing bearings of birds with coils seem to
be more consistent. Why this should be so is unclear.
Map and compass
Both clock-shifts and magnetic head coils seem to deflect
the pigeon’s vanishing bearings with respect to the home
direction. This observation provides support for Kramer’s idea
that pigeon homing is a two-step process: a ‘map’ to determine
the direction towards home and a compass to guide the bird in
that direction (Kramer, 1953). The most likely interpretation
of the clock-shift experiments is that they have introduced an
error into the sun compass system, but since the pigeon flies
off at an angle with respect to the home direction, the bird still
obviously knows the direction towards home. But a pigeon
headed towards home with a 6h clock-shift (and hence a 90˚
deflection) might be able to correct its course after a period of
flight. We tracked a small number of such birds by airplane
and, although their tracks are somewhat fragmentary, it appears
that they approach home in a converging spiral. This must
N
A
B
100km
Fig. 1. Vanishing bearings of unmanipulated
Cornell pigeons released at various locations
around their home loft in Ithaca, New York.
Each symbol represents the direction of the
mean vector of releases on 1 day. The length
of the symbol is proportional to the degree of
clumping of each day’s vanishing bearings. At
most locations, the vanishing bearings were
directed towards the home loft (filled circle
near center). But near Castor Hill on the Tug
Hill Plateau (A, 160km northnortheast of
Ithaca) pigeons tended to fly west rather than
south. At Jersey Hill Fire Tower (B, 132km
west of Ithaca), Cornell pigeons vanished
randomly.

24
mean that they continue to update the direction towards home
as they fly, each time with the same 90˚ error. If the error were
greater than 90˚, the spiral would never converge on home. If
it were less, as in a 2h shift, convergence would be rapid.
Maybe this is why many 2h shifted birds home more
successfully than birds with 6h shifts. By looking at the shape
of the spiral, one can calculate that birds with 6h shifts must
re-compute the direction towards home roughly every
15–30min.
Map cues
In Italy and Germany, a long series of ingenious experiments
has provided evidence that olfactory cues are important in
pigeon homing (for reviews, see Wallraff, 1990; Papi, 1986,
1989, 1991). Birds with their olfactory nerves sectioned neither
orient nor home from unfamiliar sites. Pigeons whose exposure
to natural air flow has been manipulated by deflector lofts or
by tunnels show the predicted deflection of their vanishing
directions. Birds transported long distances do not orient unless
they are allowed to sample the natural air on the outward
journey; filtering the air through charcoal eliminates the
pigeons’ ability to orient (Wallraff and Foà, 1981). These and
many other observations make a convincing case that pigeons
make some use of olfactory information in their orientation.
The Earth’s magnetic field is another potential ‘map’ cue.
The field varies in both strength and direction over the Earth’s
surface. A pigeon that was able to measure tiny differences in
either angle or strength of the field could, at least in theory, tell
where it was on the surface of the Earth. Wiltschko and
Wiltschko (1988) and Able (1994) have written excellent
reviews on this subject. Infrasound has also been suggested as
a potential map cue. Pigeons are sensitive to very low-
frequency sounds down to 0.1Hz. Perhaps they could use
sources of such sounds as acoustic guideposts (Yodlowski et
al. 1977; Kreithen and Quine, 1979). Pigeons can respond to
polarized light patterns (Kreithen and Keeton, 1974); they can
also detect ultraviolet light (Kreithen and Eisner, 1978). What
role these abilities might play in their orientation is completely
unclear.
Multiplicity and interaction among cues
The orientation of pigeons exposed either to clock-shifts or
to magnetic manipulations suggests that the birds know the
direction to home and that the experimental manipulations are
deflecting their vanishing bearings in relation to this home
direction. Clock-shifts and magnetic coils cause the pigeons to
select a wrong compass direction, but the errors that they make
show that the treated birds nevertheless possess information on
the direction of their home loft. If this is so, then what is the
nature of the cues that provide information on the home
direction?
Let us begin by first excluding several cues. Finding the
correct home direction does not require a view of the sun.
Pigeons select the home direction in the presence of both
Earth-strength and weaker static and varying magnetic fields
(Lednor and Walcott, 1983). This performance also does not
require acoustic cues (G. Manley, personal communication).
The results of three sets of experiments, described below,
suggest that determining the home direction is based on
redundant cues, as in the case of the compass system.
Pigeons raised in our lofts at Cornell in Ithaca, NY, are
disoriented and few home when released at Jersey Hill Fire
Tower, which is located 132km west of Ithaca. Birds raised in
other lofts, even one as close as 18km to our Cornell lofts, are
well oriented at Jersey Hill. Cornell-born pigeons raised in
other lofts are well oriented, pigeons born in other lofts and
raised at Cornell are disoriented. Clearly, being raised at the
Cornell pigeon lofts interferes with orientation at Jersey Hill
(Walcott and Brown, 1989).
In Frankfurt, Germany, pigeons raised in a loft in the
courtyard of the Zoological Institute are about equally well
oriented whether or not they are made anosmic. Their siblings
raised on the roof of the four-storey building with access to the
free winds become disoriented when made anosmic. Here, it
appears that the cues that the birds use may well depend upon
the circumstances of their rearing (Wiltschko et al. 1989;
Wiltschko and Wiltschko, 1989).
In Lincoln, Massachusetts, USA, pigeons raised in one loft
were disoriented when released at a magnetic anomaly. Their
siblings raised in a loft only 2.5km away were well-oriented
at the same anomaly. Since both releases took place under
sunny skies, when a sun compass was available, we are
tempted to suggest that one group of birds might have been
using magnetic information to find their homeward direction
while their siblings from the other loft were using some other
cue (Walcott, 1992).
Pigeon behavior differs at familiar and unfamiliar sites. For
example, pigeons released at magnetic anomalies are better
oriented on their second release at the same anomaly. Yet
experience at other anomalies does not help their performance
at a test anomaly (Lednor and Walcott, 1988). Experienced
pigeons made anosmic by olfactory nerve section or
anesthetics are disoriented at unfamiliar sites and their homing
is poor, whereas at familiar sites, the same birds both orient
and home (Streng and Wallraff, 1992). Birds that have been
raised in lofts with a view of the landscape home faster when
they are allowed to view the landscape around the release site
before beginning their flight home (Braithwaite and Newman,
1994; Braithwaite and Guilford, 1995). Clearly the birds are
learning something about the release site itself. In contrast,
pigeons released at Jersey Hill show no great improvement in
either their orientation or homing success on subsequent
releases.
Pigeons released at magnetic anomalies, once outside the
magnetically disturbed area, turn and head for home. Much the
same is true of pigeons released at Castor Hill. These birds
headed off on an incorrect course that they later corrected. In
contrast, birds tracked from Jersey Hill continued steadfastly
on their incorrect course, with only a small percentage
correcting it towards home (B. Moore and R. Madden, personal
communication). What is especially surprising about these
Cornell birds released at Jersey Hill is that they often flew over
C. WALCOTT

25Pigeon homing: sensory cues
areas from where, had they been released there in the first
place, they would have homed well. This is also true of clock-
shifted birds; airplane tracking shows that they continue on
their shifted course even over presumably familiar terrain. The
difference is that clock-shifted pigeons seem to correct their
courses, whereas birds released at Jersey Hill do not. This
difference implies that the clock-shifted birds continually
update their knowledge of the home position whereas birds
released at Jersey Hill seem to have no idea where home is
located. Why Cornell birds have such problems at Jersey Hill
is completely mysterious.
If the map is based on the comparison of some factor at the
release site with its remembered value at the home loft, then
there seem to be two categories of places. First, there are
locations where this comparison is agreed upon by all birds
from a specific loft and where they predominantly choose some
direction other than home. At Castor Hill, on the Tug Hill
plateau, Cornell birds are all agreed about the direction to fly
even though it is not the correct direction to home. Here, the
comparison of some mysterious cues leads to a consensus,
even if it is wrong (Keeton, 1973). In the second category are
release sites where the comparison does not yield useful
information. Each pigeon comes to a different conclusion
about the direction towards home, and the pigeons vanish at
random. The releases at magnetic anomalies, as well as the
Jersey Hill releases, belong to this second category. They
differ, however, in that Cornell birds released at Jersey Hill
never correct their courses and few home successfully, whereas
birds from magnetic anomalies correct their courses and home
normally.
A further interesting observation was made when pigeons
from our old Lincoln, Massachusetts, lofts that were
disoriented by magnetic anomalies were released at
magnetically normal sites but had to fly over a magnetic
anomaly on their way home. Generally, such pigeons flew on
normal, straight homeward courses. Occasionally, a pigeon
gave evidence of being disoriented by the anomaly (Fig. 6a in
Gould, 1982). This exception provides further evidence that
pigeons determine the direction to home at the release site and
only occasionally check positional information on their
homeward trip.
All of these experiments suggest that the ‘map’ or home
vector sense seems to rely on a comparison of some factor
which may depend on loft location, release site and,
presumably, available cues. Ganzhorn’s (1989, 1992) analysis
of the various release points for Cornell birds divides them into
various clusters according to the vanishing bearings of the
birds. Furthermore, he points out that magnetic manipulations
have an effect at some release sites and olfactory manipulations
at others. Clearly, the pigeons’ behavior depends on multiple
cues. Which cues they use seems to be a function of both the
loft and its location as well as of the release site (Schmidt-
Koenig and Ganzhorn, 1991). Table 1 summarizes the
different potential cues.
Much of the confusion in the pigeon homing story may well
result from the differences among various lofts and release
sites. Even such well-known and agreed upon manipulations
as clock shifts have different effects at different release sites.
Given this degree of variability, it should be no surprise that
different investigators obtain different results with pigeons
living in different areas!
References
ABLE, K. P. (1994). Magnetic orientation and magnetoreception in
birds. Prog. Neurobiol. 42, 449–473.
ALEXANDER, J. R. (1975). The effect of various phase-shifting
experiments on homing in pigeons. PhD thesis, Cornell University,
Ithaca, New York.
BRAITHWAITE, V. A. AND GUILFORD, T. (1995). A loft with a view:
Table 1. Potential cues that might be used by homing pigeons in returning to their lofts
Compass Geographic
Potential cue or map scale Evidence Certainty Review
Sun azimuth Compass Hemisphere Clock-shift High Schmidt-Koenig et al. (1991)
Sun position Map ? None Out Schmidt-Koenig (1972); Walcott (1972)
Odor, mosaic Map Local Detour Medium Papi (1991)
Site simulation
Odor, gradient Map 103km Long-distance Medium Wallraff (1990); Waldvogel (1989)
Magnetic field Compass World Magnets High Wiltschko and Wiltschko (1988)
Magnetic field Map ? Anomalies Medium Able (1994)
Visual landmarks ? Local Frosted lenses High Schlichte (1973); Braithwaite and
Guilford (1995)
Infrasound Map Long None ? Yodlowski et al. (1977); Quine (1982)
Polarized light Compass Hemisphere None Low Waldvogel (1990)
Compass or map refers to whether a cue is likely to be used for direction finding (compass) or position finding (map). Geographic scale is
the size of the region in which the cue is likely to be useful. Evidence is main experimental evidence, and certainty is the degree to which there
is general agreement that the cue is used. Review is the most current or most useful reference to the literature.

26
exposure to a natural landscape during development may encourage
adult pigeons to use visual landmarks during homing. Anim. Behav.
49, 251–253.
BRAITHWAITE, V. A. AND NEWMAN, J. A. (1994). Exposure to familiar
visual landmarks allows pigeons to home faster. Anim. Behav. 48,
1482–1484.
BRAMANTI, M., DALL’ANTONIA, L. AND PAPI, F. (1988). A new
technique to monitor the flight paths of birds. J. exp. Biol. 134,
467–472.
FIASCHI, V., BALDACCINI, N. E., IOALÈ, P. AND PAPI, F. (1981).
Helicopter observations of homing in pigeons with biased
orientation because of deflected winds at the home loft. Monitore
zool. Ital. (N.S.) 15, 139–153.
FULLER, E., KOWALSKI, U. AND WILTSCHKO, R. (1983). Orientation of
homing pigeons: compass orientation vs piloting by familiar
landmarks. J. comp. Physiol. 153, 55–58.
GANZHORN, J. U. (1989). Multivariate analysis of initial orientation in
homing pigeons: Is there a ‘preferred compass direction’? J. Orn.
130, 161–173.
GANZHORN, J. U. (1992). Geographical patterns in the initial
orientation of homing pigeons in upstate New York. Anim. Behav.
44, 931–941.
GOULD, J. L. (1982). The map sense of pigeons. Nature 296, 205–211.
GRAUE, L. C. (1963). The effect of phase shifts in the day–night cycle
on Pigeon homing at distances of less than one mile. Ohio J. Sci.
63, 214–217.
GRAUE, L. C. (1965). Initial orientation in pigeon homing related to
magnetic contours. Am. Zool. 5, 704.
GRIFFIN, D. R. (1952). Airplane observations of homing pigeons. Bull.
Mus. comp. Zool. 107, 411–440.
HITCHCOCK, H. B. (1952). Airplane observations of homing pigeons.
Proc. Am. phil. Soc. 96, 270–289.
HITCHCOCK, H. B. (1955). Homing flights and orientation in pigeons.
Auk 72, 355–373.
IOALÈ, P. (1984). Magnets and pigeon orientation. Monitore zool. Ital.
(N.S.) 18, 347–358.
KEETON, W. T. (1969). Orientation by pigeons: is the sun necessary?
Science 165, 922–928.
KEETON, W. T. (1971). Magnets interfere with pigeon homing. Proc.
natn. Acad. Sci. U.S.A. 68, 102–106.
KEETON, W. T. (1973). Release-site bias as a possible guide
to the map component in pigeon homing. J. comp. Physiol. 86,
1–16.
KRAMER, G. (1953). Wird die Sonnenhohe bei der
Heimfindeorientierung verwertet? J. Orn. 94, 201–219.
KREITHEN, M. L. AND EISNER, T. (1978). Ultraviolet light detection by
the homing pigeon. Nature 272, 347–348.
KREITHEN, M. L. AND KEETON, W. T. (1974). Detection of polarized
light by the homing pigeon, Columba livia. J. comp. Physiol. 89,
83–92.
KREITHEN, M. L. AND QUINE, D. B. (1979). Infrasound detection by
the homing pigeon: A behavioral audiogram. J. comp. Physiol. 129,
1–4.
LEDNOR, A. J. AND WALCOTT, C. (1983). Homing pigeon navigation:
the effects of in-flight exposure to a varying magnetic field. Comp.
Biochem. Physiol. 76A, 665–671.
LEDNOR, A. J. AND WALCOTT, C. (1988). Orientation of homing
pigeons at magnetic anomalies: The effects of experience. Behav.
Ecol. Sociobiol. 22, 3–8.
MICHENER, M. C. AND WALCOTT, C. (1967). Homing of single pigeons
– analysis of tracks. J. exp. Biol. 47, 99–131.
PAPI, F. (1986). Pigeon navigation: solved problems and open
questions. Monitore zool. Ital. (N.S.) 20, 471–517.
PAPI, F. (1989). Pigeons use olfactory cues to navigate. Ethol. Ecol.
Evol. 1, 219–231.
PAPI, F. (1991). Olfactory navigation. In Orientation in Birds (ed. P.
Berthold), pp. 52–85. Basel, Boston, Berlin: Birkhauser.
QUINE, D. (1982). Infrasounds: A potential navigational cue for
homing pigeons. In Avian Navigation (ed. F. Papi and H. G.
Wallraff), pp. 373–376. Berlin, Heidelberg, New York: Springer-
Verlag.
SCHLICHTE, H. J. (1973). Untersuchungen uber die Bedeutung
optischer Parameter fur das Heimkehrverhalten der Brieftauben. Z.
Tierpsychol. 32, 257–280.
SCHLICHTE, H. J. AND SCHMIDT-KOENIG, K. (1971). Zum
Heimfindevermogen der Brieftauben bei erschwerter optische
Wahrnehmung. Naturwissenschaften 58, 257–280.
SCHMIDT-KOENIG, K. (1960). Internal clocks and homing. In
Biological Clocks (ed. L. Frisch), pp. 389–393. Cold Spring
Harbor, NY: The Biological Laboratory.
SCHMIDT-KOENIG, K. (1963). On the role of the loft, the distance and
site of release in pigeon homing (The ‘cross-loft experiment’). Biol.
Bull. mar. biol. Lab., Woods Hole 125, 154–164.
SCHMIDT-KOENIG, K. (1972). New experiments on the effect of clock
shifts on homing in pigeons. In Animal Orientation and Navigation
(ed. S. R. Galler, K. Schmidt-Koenig, G. J. Jacobs and R.
Belleville), pp. 275–282. NASA SP-262.
SCHMIDT-KOENIG, K. (1990). The sun compass. Experientia 16,
336–342.
SCHMIDT-KOENIG, K. AND GANZHORN, J. U. (1991). On the problem
of bird navigation. In Perspectives in Ethology, vol. 9 (ed. P. P. G.
Bateson and P. H. Klopfer), pp. 261–283. New York, London:
Plenum Press.
SCHMIDT-KOENIG, K., GANZHORN, J. U. AND RANVAUD, R. (1991). The
sun compass. In Orientation in Birds (ed. P. Berthold), pp. 1–15.
Basel: Birkhauser Verlag.
SCHMIDT-KOENIG, K. AND WALCOTT, C. (1978). Tracks of pigeons
homing with frosted lenses. Anim. Behav. 26, 480–486.
STRENG, A. AND WALLRAFF, H. G. (1992). Attempts to determine the
roles of visual and olfactory inputs in initial orientation and homing
of pigeons over familiar terrain. Ethology 91, 203–219.
TALKINGTON, L. (1967). Bird navigation and geomagnetism. Am.
Zool. 7, 199.
VISALBERGHI, E. AND ALLEVA, E. (1979). Magnetic influences on
pigeon homing. Biol. Bull. mar. biol. Lab., Woods Hole 156,
246–256.
WALCOTT, C. (1972). The navigation of homing pigeons: do they use
sun navigation? In Animal Orientation and Navigation (ed. S. R.
Galler, K. Schmidt-Koenig, G. J. Jacobs and R. E. Belleville), pp.
283–292. NASA SP-262.
WALCOTT, C. (1977). Magnetic fields and the orientation of homing
pigeons under sun. J. exp. Biol. 70, 105–123.
WALCOTT, C. (1992). Pigeons at magnetic anomalies: the effects of
loft location. J. exp. Biol. 170, 127–141.
WALCOTT, C. AND BROWN, A. I. (1989). The disorientation of pigeons
at Jersey Hill. In Orientation and Navigation: Birds, Humans and
Other Animals. Cardiff, Wales: Royal Institute of Navigation.
WALCOTT, C. AND GREEN, R. P. (1974). Orientation of homing pigeons
altered by a change in the direction of an applied magnetic field.
Science 184, 180–182.
WALDVOGEL, J. A. (1989). Olfactory orientation by birds. In Current
Ornithology (ed D. M. Power), pp. 269–321. New York: Plenum.
C. WALCOTT

27Pigeon homing: sensory cues
WALDVOGEL, J. A. (1990). The bird’s eye view. Am. Sci. 78, 342–353.
WALLRAFF, H. G. (1979). Goal-oriented and compass-oriented
movements of displaced homing pigeons after confinement in
differentially shielded aviaries. Behav. Ecol. Sociobiol. 5, 201–225.
WALLRAFF, H. G. (1980). Does pigeon homing depend on stimuli
perceived during displacement? I. Experiments in Germany. J.
comp. Physiol. 139, 193–201.
WALLRAFF, H. G. (1990). Navigation by homing pigeons. Ethol. Ecol.
Evol. 2, 81–115.
WALLRAFF, H. G. AND FOÀ, A. (1981). Pigeon navigation: Charcoal
filter removes relevant information from environmental air. Behav.
Ecol. Sociobiol. 9, 67–77.
WALLRAFF, H. G., FOÀ, A. AND IOALÈ, P. (1980). Does pigeon homing
depend on stimuli perceived during displacement? II. Experiments
in Italy. J. comp. Physiol. 139, 203–208.
WAR DEPARTMENT (1921). United States Manual for all Pigeoneers.
Signal Corps, U.S. Army.
WAR DEPARTMENT (1945). The Homing Pigeon, Technical Manual.
Washington, DC: U.S. Government Printing Office.
WILTSCHKO, R., SCHOPS, M. AND KOWALSKI, U. (1989). Pigeon
homing: wind exposition determines the importance of olfactory
input. Naturwissenschaften 76, 229–231.
WILTSCHKO, R. AND WILTSCHKO, W. (1978). Evidence for the use of
magnetic outward-journey information in homing pigeons.
Naturwissenschaften 65, 112–113.
WILTSCHKO, R. AND WILTSCHKO, W. (1989). Pigeon homing:
Olfactory orientation – a paradox. Behav. Ecol. Sociobiol. 24,
163–173.
WILTSCHKO, W. AND WILTSCHKO, R. (1988). Magnetic orientation in
birds. In Current Ornithology, vol. 5 (ed. R. F. Johnston), pp.
67–121. New York, London: Plenum Press.
YODLOWSKI, M. L., KREITHEN, M. L. AND KEETON, W. T. (1977).
Detection of atmospheric infra-sound by homing pigeons. Nature
265, 725–726.