Posted on 09/27/2007 4:01:04 PM PDT by blam
Birds Can "See" Earth's Magnetic Field
John Roach
for National Geographic News
September 27, 2007
To find north, humans look to a compass. But birds may just need to open their eyes, a new study says.
Scientists already suspected birds' eyes contain molecules that are thought to sense Earth's magnetic field. In a new study, German researchers found that these molecules are linked to an area of the brain known to process visual information.
In that sense, "birds may see the magnetic field," said study lead author Dominik Heyers, a biologist at the University of Oldenburg.
Magnetic Orientation
Human-made compasses work by using Earth as an enormous magnet and orienting a tiny magnet attached to a needle to the planet's north and south poles.
Scientists have thought for years that migratory birds may use an internal compass to navigate between their nesting areas and wintering grounds, which can be separated by thousands of miles. (Related news: "Migrating Birds Reset 'Compasses' at Sunset, Study Says" [April 15, 2004].)
The new research helps explain how this natural compass may work.
Heyers and his colleagues injected migratory garden warblers with a special dye that can be traced as it travels along nerve fibers.
The team put one type of tracer dye into the eyes and another in a region of the brain called Cluster N, which is most active when birds orient themselves.
When the birds got their bearings, both tracers traveled to and met in the thalamus, a region in the middle of the brain responsible for vision.
"That shows there is direct linkage between the eye and Cluster N," Heyers said.
The finding strongly supports the hypothesis that migratory birds use their visual system to navigate using the magnetic field.
"The magnetic field or magnetic direction may be perceived as a dark or light spot which lies upon the normal visual field of the bird," Heyers said, "and which, of course, changes when the bird turns its head."
The study was published in a recent issue of the Public Library of Science journal PLoS ONE.
Scientists not involved with the study said it is impressive and well done, but cautioned that there are more pieces to the puzzle of how birds navigate on their long migrations.
"An animal that has to migrate over great distances needs to have both a compass and a map," said Cordula Mora, a biologist who recently completed her postdoctoral research at the University of North Carolina, Chapel Hill.
Mora's work suggests that birds may use magnetic crystals in their beaks to sense the intensity of the magnetic field and thus glean information on their physical location. (Related news: "Magnetic Beaks Help Birds Navigate, Study Says" [November 24, 2004].)
"If you have a compass, you know where north, south, east, [and] west [are], but you don't know where you are, so you don't know where you should be going," she said.
Study author Heyers said "both [map and compass] systems may act in concert."
Robert Beason is a wildlife research biologist with the U.S. Department of Agriculture in Sandusky, Ohio, and an expert on bird navigation.
He noted that stars may also either fully or in part provide the birds with their visual bearing—not the magnetic field.
The next step is to figure out where all this information comes together in the bird brain, he noted.
"That's probably going to tell us where the navigation center for birds is," he said.
God sure is something.
Amen
They got the thalamus wrong. The thalamus contains the lateral geniculate bodies, nuclei that serve to relay visual information from the optic nerve to the occipital (visual) cortex.
In another article an Atlantic tern which migrates from Nova Scotia to the North shore of South America were tested in a different manner. They were encased in a sphere which was painted black. Inorder to test the thesis, the scientists changed the day night cycle to get the bird on a standard time. When migration is about to begin the bird's genetalia shrink. Thus there is less body weight for the long migration. The sphere that housed the birds had minute holes which were made so that the Northern Hemisphere Celestial Sphere was portrayed. The inside of the shpere was covered with carbon paper and as the migration began the birds would try to launch themselves southward. From the bird tracks in the sphere the scientists concluded that these birds also performed a rudimentary form of celestial navigation.
Ain't it amazin'?
So all we have to do is figure out a way to manipulate the earth’s magnetic field and we can drive all these dammed Canadian Geese from the South?
We already knew that birds could read Earth's manetic lines, and celestial navigation would be important as birds migrate at night. That birds see magnetic lines and navigate by stars is new.
By the way, UNC/Chapel Hill, is active in some elegant studies to determine just how closely birds evolved from dinosaurs. I don't agree with their findings, but their bird limb ontogony observations were very nicely done. I agree with this observer: http://www.dinosauria.com/jdp/archie/paulfed.html
What happens if the Earth’s magnetic field reverses?
Nature adapts. The field has changed a lot during earth’s history, and life is still here! BTW, bird may be able to see the magnetic field, and shark can sense it in other ways, but us Humans got the wonder of the color spectrum.
So, what are the birds going to do when the magnetic field drops to near zero the next few years?
Or, in a equally bad case, when the north magnetic pole moves sideways from Hudson Bay so far the birds end up in Seattle rather than mid-Manitoba.
All birds will fly backwards?
Where you gonna drive them? Here in Michigan they're all over the darn place, we don't have any room left for your geese. Maybe thats why they're down with you.........
They return north the same way, using the air currents.
It might be possible to train a bird to respond to radio signals. Someone with lots of time on their hands could put out bird food randomly along with various strong radio signals and see who shows up. Hmmm, I'll change my voter registration to Democrat, apply for a government grant and take a really long vacation. I have to work global warming into the grant request somehow.
Very cool!
Changing the magnetic field wouldn't help a bit around here.
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