161
of leatherback sea turtle ( D. coriacea ) because of their excellent orientation using
geomagnetic fi eld. These observations suggest that “light- dependence is not a
universal feature of vertebrate magnetic compasses,” (Lohmann and Lohmann 1993 ).
Young turtles that reside in coastal feeding grounds make a more sophisticate use of
Earth’s magnetic fi eld. Instead of simply responding to boundaries delineated by
magnetic fi elds, older turtles appear to learn the magnetic topography of their feeding
grounds (Perry 1982 ). Magnetic cues aide them in navigating back to particular sites.
These magnetic maps were shown to exist by subjecting juvenile green turtles
( Chelonia mydas ) to magnetic fi elds situated in locations to the north or south of their
territory (Perry 1982 ). Turtles tethered in water close to their familiar feeding areas
that were exposed to the northern fi elds swam south, and those exposed to a fi eld in
the south swam north (Perry 1982 ). This seems to indicate that the turtles were gaining
positional information from the Earth’s magnetic fi eld and using this as a map to aid
in their navigation (Perry 1982 ). It is not known if adults use this magnetic map for
homing in on their natal beaches. It is reasonable to theorize that turtles imprint on
the magnetic fi ngerprint for their birth territory, and use this information to guide
them back to these regions when it comes time to reproduce (Lohmann and Lohmann
2006 ). If used, these magnetic maps may also be combined with chemical and visual
landmarks to provide more accurate navigation (Lohmann and Lohmann 2006 ).
There are numerous works regarding magnetite and related topics in turtles
(Kirschvink 1980 ; Perry et al. 1985 ; Mathis and Moore 1988 ; Lohmann 1991 ;
Lohman and Lohman 1994 ; Courtillot et al. 1997 ; Lohmann et al. 2001 , 2004 ).
It seems clear that turtles use a ferromagnetic receptor, however, how sea turtles can
sense the Earth’s magnetic fi eld in detail remains a mystery.
3.5.3 Magnetite in Sea Birds
There are two hypothesis concerning bird’s “magnetic feeling”. According to the
fi rst suggestion, specialized iron-rich cells are responsible for the phenomenon.
The second theory “involves the spin of electrons, which is known to be affected
by magnetic fi elds. Because this process requires light, molecules in birds’ eyes
may be receptive to magnetism,” (Hamzelou 2012 ; see for more information
Phillips 1996 ; Deutschlander and Muheim 2010 ). Thus, the magnetic compass of
several bird species has been characterized as a so-called inclination compass,
since it is based “on the axial course of the fi eld lines and their inclination in
space,” (Davila 2005 ). According to the inclination compass model, the polarity
of the vector is irrelevant: reversing the horizontal component has the same effect
as reversing the vertical component. Reversal of both components, implying an
inversion in the polarity of the fi eld while maintaining the direction of the fi eld
lines, does not alter the behavior of the birds (Wiltschko and Wiltschko 1972 ).
Behavioral and electrophysiological experiments in migrating and homing birds
suggest that the inclination compass of birds may be related to the optic system
(Wiltschko and Wiltschko 1981 ).
3.5 Biomagnetite in Marine Vertebrates
of leatherback sea turtle ( D. coriacea ) because of their excellent orientation using
geomagnetic fi eld. These observations suggest that “light- dependence is not a
universal feature of vertebrate magnetic compasses,” (Lohmann and Lohmann 1993 ).
Young turtles that reside in coastal feeding grounds make a more sophisticate use of
Earth’s magnetic fi eld. Instead of simply responding to boundaries delineated by
magnetic fi elds, older turtles appear to learn the magnetic topography of their feeding
grounds (Perry 1982 ). Magnetic cues aide them in navigating back to particular sites.
These magnetic maps were shown to exist by subjecting juvenile green turtles
( Chelonia mydas ) to magnetic fi elds situated in locations to the north or south of their
territory (Perry 1982 ). Turtles tethered in water close to their familiar feeding areas
that were exposed to the northern fi elds swam south, and those exposed to a fi eld in
the south swam north (Perry 1982 ). This seems to indicate that the turtles were gaining
positional information from the Earth’s magnetic fi eld and using this as a map to aid
in their navigation (Perry 1982 ). It is not known if adults use this magnetic map for
homing in on their natal beaches. It is reasonable to theorize that turtles imprint on
the magnetic fi ngerprint for their birth territory, and use this information to guide
them back to these regions when it comes time to reproduce (Lohmann and Lohmann
2006 ). If used, these magnetic maps may also be combined with chemical and visual
landmarks to provide more accurate navigation (Lohmann and Lohmann 2006 ).
There are numerous works regarding magnetite and related topics in turtles
(Kirschvink 1980 ; Perry et al. 1985 ; Mathis and Moore 1988 ; Lohmann 1991 ;
Lohman and Lohman 1994 ; Courtillot et al. 1997 ; Lohmann et al. 2001 , 2004 ).
It seems clear that turtles use a ferromagnetic receptor, however, how sea turtles can
sense the Earth’s magnetic fi eld in detail remains a mystery.
3.5.3 Magnetite in Sea Birds
There are two hypothesis concerning bird’s “magnetic feeling”. According to the
fi rst suggestion, specialized iron-rich cells are responsible for the phenomenon.
The second theory “involves the spin of electrons, which is known to be affected
by magnetic fi elds. Because this process requires light, molecules in birds’ eyes
may be receptive to magnetism,” (Hamzelou 2012 ; see for more information
Phillips 1996 ; Deutschlander and Muheim 2010 ). Thus, the magnetic compass of
several bird species has been characterized as a so-called inclination compass,
since it is based “on the axial course of the fi eld lines and their inclination in
space,” (Davila 2005 ). According to the inclination compass model, the polarity
of the vector is irrelevant: reversing the horizontal component has the same effect
as reversing the vertical component. Reversal of both components, implying an
inversion in the polarity of the fi eld while maintaining the direction of the fi eld
lines, does not alter the behavior of the birds (Wiltschko and Wiltschko 1972 ).
Behavioral and electrophysiological experiments in migrating and homing birds
suggest that the inclination compass of birds may be related to the optic system
(Wiltschko and Wiltschko 1981 ).
3.5 Biomagnetite in Marine Vertebrates