I was discussing this with another friend and it got me thinking (I know, a dangerous thing!)... here is part of the conversation:
ACME wrote:yes, many birds, sea mammals, reptiles, fish have migratory ranges that rely on something other than google navigation for getting to the right place 2,000- 5,000 miles away. . . not sure magnetic fields is the most efficient intraplanet guidance construct; seems there'd be a fair amount of variation over time, and a fair number of gravitational lines that don't look discrete to the undiscerning eye .
lots of insects have multi thousand mile migrations, also. . . guess it could all be the same mechanism; guess we'll have to wait to find out whether locusts and monarchs have the same proteins as birds. . .
somehow, i think it has to be something more sensitive, discrete & constant than magnetic perception. . . a quelea may migrate thousands of miles, but it also has pretty fine abilities to find its own nest when nests can be stacked 10 - 20 per cubic meter in a flock of a couple million birds. . do you think ordinary magnetism is the right base guidance grid for that kind of precision?
There are probably a number of mechanisms at work for nest location. I grew up on the Connecticut shore and spent plenty of time on the ocean; my father loved sailing and my grandfather loved to fish. I know how to do celestial navigation, but that is only an approximation of position--you still need to find some physical landmark to get home. I think magnetic perception is similar--it allows approximate positioning, but then other factors take over to identify a nest in the "near field," just like spotting the lighthouse at Montauk point will always get you home.
Another seaman analogy would be that magnetism is a volumetric function, and if you could sense it, all you would get is a "fog." And if you've been on the ocean, you cannot navigate in fog--yet birds are doing it. They must have developed a way to see through the magnetic fog and determine lines of force at a distance.
The only analogy I can find in nature comes from whales and dolphins that use echo-location. The deep ocean is very much like a fog as well; visibility is very limited so another mechanism needs to be used to get around. We know from electric eels and pistol shrimp that nature can develop some interesting organs... I suspect that birds are also "transmitting" some kind of magnetic echo-location against the magnetic field, perhaps looking for magnetic anomalies as reference points. The Earth's magnetic field is far from smooth--it is polyhedral and there are "magnetic vortices" all over--places like Sedona or the Bermuda triangle being some of the large ones. There may actually be a "magnetic terrain" that is invisible to us--but visible to them. Of course, our technology is damaging that, but if the changes are slow enough, I'm sure they adapt.
The concept of a magnetic terrain (and perhaps electric one, too) is not something I have considered before. Gravity does it (mascons
in astronomy), so why not a 2D and 1D version of the same thing?
I do not know if there is any commercial application, but it would be nice for my magnetic experiments to actually SEE the fields interacting in the basement, from the wiring, planet and other sources. Then one could find ways to isolate the system (magnetic-cancelling headset, so to speak), which could also have huge health benefits, since more and more research is showing that EM fields are massively disrupting biological function--invisibly. Heck, France has now banned wireless in schools because of it.
Every dogma has its day...