[Paleopsych] SW: Pigeon Homing and Highways
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Animal Cognition: Pigeon Homing and Highways
http://scienceweek.com/2005/sc050211-1.htm
The following points are made by H-P. Lipp et al (Current Biology 2004
14:1239):
1) The most widely accepted explanation for pigeon homing over
distances of 20 km and more is that they rely on a "map-and-compass"
strategy. It has remained undisputed that pigeons have an internal
clock and an internal sense of compass direction home and that this
latter sense depends on the position of the sun, if visible. Yet
directional knowledge alone is not sufficient for successful homing,
and so pigeons must also have a large-scale mental map containing
information about their current position with regard to their loft
[1].
2) Mechanisms of position determination and the nature of the mental
map used by homing pigeons have remained controversial for decades.
Supporters of the magnetic theory of pigeon homing claim a predominant
role of the earth's magnetic field for both compass and map mechanisms
[2]. Others propose a major role of the olfactory system and
atmospheric gradients [3,4]. Although vision is helpful yet not
mandatory for successful long-distance homing [5], there is general
agreement that pigeons rely at least partially on visual cues for
flights within their familiar home range, 2-4 km around the loft.
Whether the local visual information is used by the birds for homing
from distant release sites -- a strategy coined "pilotage" -- has been
equally controversial [2].
3) Likewise, the nature of the objects used by pigeons for pilotage
has been debated. Breeders of racing pigeons have often observed that
large flocks of homing pigeons fly along major highways, and it is a
familiar observation for most pigeon breeders that the birds often do
not approach the home loft according to a straight compass direction
from the release site. Early attempts to identify topographic
guide-rails used by homing pigeons (e.g., roads, railways, powerlines)
by means of airplane tracking have yielded equivocal results. Some
studies reported positive evidence; helicopter tracking studies even
found that pigeons were circling over road crossings. However, even in
these positive cases, observations were rare and anecdotal.
4) The authors present an analysis of 216 GPS-recorded pigeon tracks
over distances up to 50 km. Experienced pigeons released from familiar
sites during 3 years around Rome, Italy, were significantly attracted
to highways and a railway track running toward home, in many cases
without anything forcing them to follow such guide-rails. Birds often
broke off from the highways when these veered away from home, but many
continued their flight along the highway until a major junction, even
when the detour added substantially to their journey. The degree of
road following increased with repeated releases but not flight length.
Significant road following (in 40%-50% of the tracks) was mainly
observed from release sites along northwest-southeast axis.
5) The authors suggest their data demonstrate the existence of a
learned road-following homing strategy of pigeons and the use of
particular topographical points for final navigation to the loft.
Apparently, the better-directed early stages of the flight compensated
the added final detour. During early and middle stages of the flight,
following large and distinct roads is likely to reflect stabilization
of a compass course rather than the presence of a mental roadmap. A
cognitive (roadmap) component manifested by repeated crossing of
preferred topographical points, including highway exits, is more
likely when pigeons approach the loft area. However, it might only be
expected in pigeons raised in an area characterized by navigationally
relevant highway systems.
References (abridged):
1. Gould, J.L. (2004). Animal navigation. Curr. Biol. 14, R221-R224
2. Wiltschko, R. and Wiltschko, W. (2003). Avian navigation: from
historical to modern concepts. Anim. Behav. 65, 257-272
3. Papi, F. (1990). Olfactory navigation in birds. Experientia 46,
352-363
4. Wallraff, H.G. (2004). Avian olfactory navigation: its empirical
foundation and conceptual state. Anim. Behav. 67, 189-204
5. Schmidt-Koenig, K. and Schlichte, H.-J. (1972). Homing in pigeon
with impaired vision. Proc. Natl. Acad. Sci. USA 69, 2446-2447
Current Biology http://www.current-biology.com
--------------------------------
Related Material:
ANIMAL BEHAVIOR: ON MAGNETORECEPTION IN THE HOMING PIGEON
The following points are made by C.V. Mora et al (Nature 2004
432:508):
1) Two conflicting hypotheses compete to explain how a homing pigeon
can return to its loft over great distances. One proposes the use of
atmospheric odors[1] and the other the Earth's magnetic field[2-4] in
the "map" step of the "map and compass" hypothesis of pigeon
homing[5]. Although magnetic effects on pigeon orientation provide
indirect evidence for a magnetic "map", numerous conditioning
experiments have failed to demonstrate reproducible responses to
magnetic fields by pigeons. This has led to suggestions that homing
pigeons and other birds have no useful sensitivity to the Earth's
magnetic field.
2) The authors made a series of modifications to an existing operant
conditioning procedure to fulfill two conditions that seem to be vital
for magnetic discrimination learning in non-avian species. These are
that (1) the magnetic stimulus discriminated is a localized,
non-uniform magnetic anomaly superimposed on the uniform background
field of the Earth, and (2) movement by the experimental subjects is
necessary to produce the behavioral response measured in the
experiments. Although this combination of experimental parameters
mitigates against rapid achievement of powerful discrimination by
separating the stimulus, response and reinforcement in both space and
time --compared with standard key-pecking experiments -- failure to
fulfill either or both of the above conditions has characterized all
the unsuccessful or irreproducible attempts to condition pigeons and
many other species to magnetic fields.
3) Using a Yes-No signal-detection procedure, four individually
trained pigeons were required to discriminate between the presence and
absence of an induced magnetic field anomaly while freely walking in a
wooden tunnel. The intensity profile of the anomaly was "wave-shaped"
and peaked in the center of the tunnel at 189 micro tesla (microT)
(background level of 44 microT) with an inclination of -80 deg
(background level of -64 deg). The birds were conditioned to jump onto
a platform at one end of the tunnel when the anomaly was present and
onto an identical platform at the other end of the tunnel when the
anomaly was absent. Choice of the correct platform was rewarded with
food whereas incorrect choices were punished with a time penalty.
4) In summary: The authors demonstrate that homing pigeons (Columba
livia) can discriminate between the presence and absence of a magnetic
anomaly in a conditioned choice experiment. This discrimination is
impaired by attachment of a magnet to the cere (part of the beak),
local anaesthesia of the upper beak area, and bilateral section of the
ophthalmic branch of the trigeminal nerve, but not of the olfactory
nerve. These results suggest that magnetoreception (probably
magnetite-based) occurs in the upper beak area of the pigeon.
Traditional methods of rendering pigeons anosmic might therefore cause
simultaneous impairment of magnetoreception so that future orientation
experiments will require independent evaluation of the pigeon's
magnetic and olfactory systems.
References (abridged):
1. Papi, F., Fiore, L., Fiaschi, V. & Benvenuti, S. Olfaction and
homing in pigeons. Monit. Zool. Ital. (N.S.) 6, 85-95 (1972)
2. Gould, J. L. The case for magnetic sensitivity in birds and bees
(such as it is). Am. Sci. 68, 256-267 (1980)
3. Moore, B. R. Is the homing pigeon's map geomagnetic? Nature 285,
69-70 (1980)
4. Walcott, C. Magnetic orientation in homing pigeons. IEEE Trans.
Magnet. 16, 1008-1013 (1980)
5. Kramer, G. Wird die Sonnenhöhe bei der Heimfindeorientierung
verwertet? J. Ornithol. 94, 201-219 (1953)
Nature http://www.nature.com/nature
--------------------------------
Related Material:
MAGNETITE IN A VERTEBRATE MAGNETORECEPTOR
Notes by ScienceWeek:
An enormous variety of what are essentially experiments in viability
has occurred during the more than 3.5 billion years of biological
evolution on Earth, and among these experiments is a striking
diversity of biological devices that function to sense changes in the
environment of the organism. Consider, for example, magnetic field
detection:
The following points are made by C.E. Diebel et al (Nature 2000
406:299):
1) The key behavioral, physiological, and anatomical components of a
magnetite-based magnetic sense have been previously demonstrated in
rainbow trout (Oncorynchus mykiss), with candidate receptor cells
located within a discrete sub-layer of the olfactory tissues
(olfactory lamellae) in the nose of the trout. These receptor cells
were shown to contain iron-rich crystals similar in size and shape to
magnetite crystals extracted from salmon.
2) The authors now demonstrate that these crystals, mapped to
individual receptors by *confocal and atomic force microscopy, are
magnetic: the crystals are uniquely associated with dipoles detected
by *magnetic force microscopy. Analysis of their magnetic properties
identifies the crystals as *single-domain magnetite particles. In
addition, 3-dimensional reconstruction of the candidate receptors
using confocal and atomic microscopy imaging confirm that several
magnetite crystals are arranged in a chain of approximately 1 micron
length within the receptor, and that the receptor is a multi-lobed
single cell.
3) The authors suggest these results are consistent with a
magnetite-based detection mechanism, since 1-micron chains of
single-domain magnetite crystals are highly suitable for the
behavioral and physiological responses to magnetic intensity
previously reported for the trout.
4) The authors conclude that "understanding should now be sought of
how the chains of crystals could transduce a magnetic field into an
electrical signal in the nervous system."
Nature http://www.nature.com/nature
--------------------------------
Notes by ScienceWeek:
confocal and atomic force microscopy: In general, a "confocal
microscope" is a microscope in which an aperture in the illuminating
system confines the illumination to a small spot on the specimen, and
a corresponding aperture in the imaging system (which may be the same
aperture in reflecting and fluorescence devices) allows only light
transmitted, reflected, or emitted by the same spot to contribute to
the image. By suitable mechanical or optical means, the spots are made
to scan the specimen as in a television raster. Compared to
conventional microscopy, confocal techniques offer improved resolution
and improved rejection of out-of-focus noise. In atomic force
microscopy, a tip is fixed to a cantilever whose position is monitored
while the tip scans the surface. The force between the tip and the
surface determines the position of the cantilever. When recorded in
atomic resolution, the image represents a map of atomic forces at the
surface. The advantage of atomic force microscopy is that the probed
surface does not need to be electrically conducting.
magnetic force microscopy: This technique is capable of determining
magnetic domain structure in a variety of magnetic materials,
including small particles with a spatial resolution of less than 100
nanometers. Because it is sensitive to magnetic forces, the technique
can also image magnetic structures that are covered by a layer of
non-magnetic material.
single-domain magnetite particles: An oxide of iron, magnetite
(magnetic iron ore) is attracted by a magnet but does not attract
particles of iron to itself. In this context, the term "domain" refers
to a region in which magnetic moments are uniformly arrayed.
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