Do some species of birds use the earths magnetic field for navigation?
This has been the subject of debate for over 50 years now--I wrote
about research in this area already in 1978--and the evidence gathered
points in many directions. Some researchers have shown that
star-moon-geomarkers may be involved (again, only in certain species)
while other groups have found bio-magnetic associations. This recent
study from Germany adds more fuel to the debate on birds and bio- and
geo-magnetism. I also enclose info on the PLOS online journals, which
may interest several in this group.

Scott Hill
frontier sciences group
Copenhagen

Migrating Birds "See" the Earth's magnetic Field, Scientists Report

Alyn_walsh_2 Scientists have known for many years that birds use an
internal magnetic compass to navigate on their epic annual journeys.
But exactly how the system works has been a mystery.

Migrating birds, Reuters reports, can "see" the Earth's magnetic field
which they use as a compass to guide them around the globe.
Specialized neurons in the eye, sensitive to magnetic direction, have
been shown for the first time to connect via a specific brain pathway
to an area in the forebrain of birds responsible for vision, German
researchers, Dominik Heyers and colleagues at the University of
Oldenburg report.

Magnetic sensing molecules in the eye, known as cryptochromes, appear
to stimulate photoreceptors depending on the orientation of the
magnetic field.

This strongly suggests migratory birds perceive the magnetic field as
a visual pattern, the researchers said.

"It's a pity we cannot ask them, but what we imagine is that it is
like a shadow or a light spot on the normal vision of the bird,"
Heyers said in a telephone interview.

The German team, which published their findings in the online Public
Library of Science journal PLoS ONE, based their research on
laboratory studies of the garden warbler, a highly migratory bird.

Posted by Jason McManus.

Reuters Story Link

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THE SCIENCE CORNER

by Nigel Bunce and Jim Hunt
College of Physical Science
University of Guelph
Thur. Aug. 9, 1984

ANIMAL MAGNETISIM

The homing and directional abilities of many birds, animals, and
insects has long been a source of wonder to many and a mystery to
scientists. In recent years, some progress has been made in certain
instances. For example, it is now well established that some birds
navigate during migration by observing the shape of the stellar
constellations. It has long been suspected that the Earth's magnetic
field somehow plays a role in this navigational ability but solid
evidence has been hard to find.

It has been known for some time that the heads of pigeons and the
bodies of honey bees contain small amounts of iron oxide. One form of
iron oxide is the mineral "magnetite", which under the name
"lodestone" was used as the first compasses by the Chinese and early
mariners. The presence of magnetic material does not, however,
establish the existence of magnetic sense organs.

A big step forward was made in 1980 with the discovery of magnetic
bacteria. These creatures have solved the difficult problem of
biochemically assembling single crystals of magnetite and using them
to tell north from south and up from down.

In a recent issue of Science, a Hawaii-California group of marine
biologists report the finding of the magnetic sense organ in the
Yellowfin Tuna. The detection and localization of this material is a
very difficult problem. Where do you look, a tuna is a large fish.
Every portion of the body of the tuna had to be treated and sectioned
with non-iron instruments in a very clean environment and magnetic
measurements made on each sample.

At last magnetic material was discovered in the head in special
sinus cavities which are near large and important nerves. The
extracted material is very much like that in the bacteria. It consists
of single crystals of magnetite about two millionths of an inch
across. Somehow the growth of these crystals is biochemically
controlled and then stopped when they are just the right size. If the
crystals were any bigger, they would divide into two (or more)
magnetic domains with opposite magnetization and the magnetic effect
would cancel out. As yet the structure and operation of the whole
sense organ is unknown. Similar crystals have been found in a similar
sinus in the Chinook salmon.

In a recent issue of Nature, two biologists in New York have
reported similar studies on the bobolink which has the longest
migration path of any New World land bird.

In this case, individual crystals of magnetite have not been
isolated, but the chemical, iron oxide, from which magnetite is
made,has been identified. In this study, however, the material has
been more minutely localized. The magnetic material lies in tissues
around the olfactory (smell-sensing) nerve and on tiny bristles which
project into the nasal cavity.

The latter discovery can at least suggest a mechanism for
detecting the direction of the Earth's magnetic field. Imagine that
the bird flies in some direction with respect to the magnetic field
and then changes direction. The change will cause the small magnets in
the bristles to twist the bristles slightly and nerve cells in the
bristle could detect this twist.

It may be that at last we are getting closer to a better
understanding of animal navigation by magnetism.