162
Physiological aspects of magnetite-based receptors as well as their distribution
in birds are described in detail by Beason and Semm ( 1987 ). For example, “in the
bobolink [Dolichonyx oryzivorus] , a migratory bird. In this case, magnetic material
thought to be magnetite has been detected in an area of the upper beak. As in the
trout, the region that contains the putative magnetite appears to be innervated by the
ophthalmic branch of the trigeminal nerve. Specifi c neurons in the trigeminal ganglion, to which the ophthalmic nerve projects, respond to changes in vertical fi eld
intensity as small as about 0.5 % of the Earth’s fi eld,” (Lohmann and Johnsen 2000 ;
see also Semm and Beason 1990 ).
Recently, Cadiou and McNaughton ( 2010 ) described differences between birds
and fi sh concerning the putative magnetoreceptor cells as follow:
(i) “in birds, magnetite is located in nerve terminals, whereas in the fi sh it appears
to be located in the cell soma;
(ii) birds appear to use SPM magnetite, while fi sh use single-domain magnetite;
(iii) the magnetoreceptors are in the beak of birds but in the olfactory mucosa in
fi sh,” (Cadiou and McNaughton 2010 ).
Very recently, Treiber et al. ( 2012 ) showed, however, that the iron-rich cells with
location in the rostro-medial upper beak of the pigeon Columbia livia are not
magnetosensitive neurons. They are rather microphagous! Here, the sensation as
reported: “Ultrastructure analysis of these cells, which are not unique to the beak,
showed that their subcellular architecture includes ferritin-like granules, siderosomes,
haemosiderin and fi lopodia, characteristics of iron-rich macrophages,” (Treiber
et al. 2012 ). Thus, this novel publication necessitates a traditional view for the true
magnetite-dependent magnetoreceptors in birds. Recording from the brainstem
within conscious pigeons, it was shown the presence of specialized neurons in the
pigeon’s brain that “encode the inclination angle and intensity of the geomagnetic
fi eld,” (Vignieri 2012 ). These authors suggested that birds “can develop an internal
model of geopositional latitude to facilitate spatial orientation and navigation based
on magnetoreception,” (Vignieri 2012 ; see also Wu and Dickman 2012 ).
The debate about optical pumping boils down to whether or not there is magnetite in the retina of Vertebrates. Walker reported that in Fish (Kirschvink et al.
1985a ) and note that none of the ‘critical’ experiments using Rf magnetic fi elds on
birds was done using double-blind techniques (Kirschvink et al. 2010 ). Numerous
papers have been published on magnetite and magnetoreception in birds (Kirschvink
1982 ; Alerstam and Hogstedt 1983 ; Wiltschko and Wiltschko 1988 ; Edwards et al.
1992 ; Munro et al. 1997 ; Lohmann and Johnsen 2000 ; Wiltschko et al. 2002 , 2009 ;
Ritz et al. 2000 , 2004 ; Davila et al. 2003 ; Mouritsen and Ritz 2005 ; Cadiou and
McNaughton 2010 ; Falkenberg et al. 2010 ), however, with dominance to pigeons
(Viguier 1882 ; Keeton 1971 ; Walcott and Green 1974 ; Bookman 1977 ; Leask 1977 ;
Hanzlik et al. 2000 ; Winklhofer et al. 2001 ; Fleissner et al. 2003 ; Mora et al. 2004 ;
Biro et al. 2007 ; Tian et al. 2007 ; Dennis et al. 2007 ; Treiber et al. 2012 ; Wu and
Dickman 2012 ) and migratory songbirds (see for review Wiltschko and Wiltschko
1972 ; Beason et al. 1995 ; Wiltschko et al. 2002 ; Deutschlander and Muheim 2010 ).
Unfortunately, to my best knowledge, there are no papers on magnetite in sea birds.
3 Biocomposites and Mineralized Tissues
Physiological aspects of magnetite-based receptors as well as their distribution
in birds are described in detail by Beason and Semm ( 1987 ). For example, “in the
bobolink [Dolichonyx oryzivorus] , a migratory bird. In this case, magnetic material
thought to be magnetite has been detected in an area of the upper beak. As in the
trout, the region that contains the putative magnetite appears to be innervated by the
ophthalmic branch of the trigeminal nerve. Specifi c neurons in the trigeminal ganglion, to which the ophthalmic nerve projects, respond to changes in vertical fi eld
intensity as small as about 0.5 % of the Earth’s fi eld,” (Lohmann and Johnsen 2000 ;
see also Semm and Beason 1990 ).
Recently, Cadiou and McNaughton ( 2010 ) described differences between birds
and fi sh concerning the putative magnetoreceptor cells as follow:
(i) “in birds, magnetite is located in nerve terminals, whereas in the fi sh it appears
to be located in the cell soma;
(ii) birds appear to use SPM magnetite, while fi sh use single-domain magnetite;
(iii) the magnetoreceptors are in the beak of birds but in the olfactory mucosa in
fi sh,” (Cadiou and McNaughton 2010 ).
Very recently, Treiber et al. ( 2012 ) showed, however, that the iron-rich cells with
location in the rostro-medial upper beak of the pigeon Columbia livia are not
magnetosensitive neurons. They are rather microphagous! Here, the sensation as
reported: “Ultrastructure analysis of these cells, which are not unique to the beak,
showed that their subcellular architecture includes ferritin-like granules, siderosomes,
haemosiderin and fi lopodia, characteristics of iron-rich macrophages,” (Treiber
et al. 2012 ). Thus, this novel publication necessitates a traditional view for the true
magnetite-dependent magnetoreceptors in birds. Recording from the brainstem
within conscious pigeons, it was shown the presence of specialized neurons in the
pigeon’s brain that “encode the inclination angle and intensity of the geomagnetic
fi eld,” (Vignieri 2012 ). These authors suggested that birds “can develop an internal
model of geopositional latitude to facilitate spatial orientation and navigation based
on magnetoreception,” (Vignieri 2012 ; see also Wu and Dickman 2012 ).
The debate about optical pumping boils down to whether or not there is magnetite in the retina of Vertebrates. Walker reported that in Fish (Kirschvink et al.
1985a ) and note that none of the ‘critical’ experiments using Rf magnetic fi elds on
birds was done using double-blind techniques (Kirschvink et al. 2010 ). Numerous
papers have been published on magnetite and magnetoreception in birds (Kirschvink
1982 ; Alerstam and Hogstedt 1983 ; Wiltschko and Wiltschko 1988 ; Edwards et al.
1992 ; Munro et al. 1997 ; Lohmann and Johnsen 2000 ; Wiltschko et al. 2002 , 2009 ;
Ritz et al. 2000 , 2004 ; Davila et al. 2003 ; Mouritsen and Ritz 2005 ; Cadiou and
McNaughton 2010 ; Falkenberg et al. 2010 ), however, with dominance to pigeons
(Viguier 1882 ; Keeton 1971 ; Walcott and Green 1974 ; Bookman 1977 ; Leask 1977 ;
Hanzlik et al. 2000 ; Winklhofer et al. 2001 ; Fleissner et al. 2003 ; Mora et al. 2004 ;
Biro et al. 2007 ; Tian et al. 2007 ; Dennis et al. 2007 ; Treiber et al. 2012 ; Wu and
Dickman 2012 ) and migratory songbirds (see for review Wiltschko and Wiltschko
1972 ; Beason et al. 1995 ; Wiltschko et al. 2002 ; Deutschlander and Muheim 2010 ).
Unfortunately, to my best knowledge, there are no papers on magnetite in sea birds.
3 Biocomposites and Mineralized Tissues