Sea turtles have the remarkable ability to identify their geographical location in magnetic terms, and use this knowledge to move in consciously desired directions
IN A life span of 60-70 years, a turtle may
travel thousands of kilometers from its
birthplace, but it always finds its way
back to the same spot or someplace
close to it, whenever it lays eggs. This
intriguing and unerring instinct is now
being attributed to the fact that turtles
rely on the earth's magnetic field to
reach their destination. This finding was
made by Kenneth J Lohmann and
Catherine M F Lohmarni - biologists
at the University of North Carolina in
Chapel Hill, us - who conducted
experiments on just-hatched loggerhead
turtles (large-headed sea turtles of warm
seas). Earlier, the husband-wife team
had demonstrated that loggerheads can
determine the inclination (the dip or
deviation from the magnetic field of the
earth).
According to Kenneth Lohmann,
the intensity of the magnetic field and
the inclination of the region in which
the turtles travel, are both inconstant
because they vary with changing directions. They form a sort of a grid, much
like the on6 made by latitudes and longitudes. Therefore, any 'point on the
earth is marked by both the magnetic
intertsity and inclination. Since turtles
can make out both these features, in all
possibility they must be mentally creating a 'magnetic map' and using it to get
around.
The biologists devised a small circular, pool fitted with an electric coil to
simulate a magnetic field. The loggerheads which the Lohmanns studied,
hatched on the beaches of Florida in the
us and would be speAding their lives
swimming in the subtropical gyre found
between North America and Africa
(Wind stress induces a circulation pattern which is similar for every ocean in
the world. Wind-driven circulation is
divided into large gyres that stretch
across entire oceans. Subtropical gyres
are those that extend from the equatorial current system to a maximum latitude of 50 degrees. And in this case, the
subtropical gyre found in this area is the
gulf stream). Two magnetic fields were
chosen; one that corresponded to a
point off the Carolinas in the Lis on the
western side of the gyre, and the other to
the gyre's eastern edge. When two or
three-day-old hatchlings were placed in
the pool and exposed to the field corresponding to the gyre's western side, the
turtles swam eastwards. And they paddled off in the westerly direction when
the magnetic field was changed and
both these movements were made by
the turtle in an effort to stay within the
gyre. Any aberration and the turtles
would move fatally into the icy waters,
north of the gyre. it was interesting to
note that even these jUst-born turtles
that were being exposed to these
magnetic intensities for the first time,
moved in the manner they did.
Lohmano feels that the newborns
were "pre-programmed to swim in a
particular direction". The couple
suggest that on hatching, the magnetic
features of the nesting ground are
imprinted on the brain of the yourtgone
so that it develops a broader magnetic
map. The creature reaches the vicinity
of the beach with the help of this map,
and thereafter other instincts like its
sense of smell guide it homewards.
According to Kenneth P Able, a
biologist with the State University of
New York at Albany, is, and an expert
on animal navigation, that the animals
use the earth's magnetic field to move in
a certain direction, is not news. Rather,
what is interesting in the Lohmantis'
study, is the ability of the turtle to locate
itself on a map. According to him, "This
is the first good empirical evidence of
the animal doing something sophisticated with the magnetic field".
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