Loggerhead turtles have internal GPS

New Scientist has a great set of stories about the extraordinary senses of animals, including the fact that creatures like sea turtles can sense the Earth's magnetic field and use it for navigation.

Young loggerhead turtles, for example, read the Earth's magnetic field to adjust the direction in which they swim. They seem to hatch with a set of directions, which, with the help of their magnetic sense, ensures that they always stay in warm waters during their first migration around the rim of the North Atlantic. Over time they build a more detailed magnetic map by learning to recognise variations in the strength and direction of the field lines, which are angled more steeply towards the poles and flatter at the magnetic equator.

What isn't known, however, is how they sense magnetism. Part of the problem is that magnetic fields can pass through biological tissues without being altered, so the sensors could, in theory, be located in any part of the body. What's more, the detection might not need specialised structures at all, but may instead be based on a series of chemical reactions.

Even so, many researchers think that magnetic receptors probably exist in the head of turtles and perhaps other animals. These might be based on crystals of magnetite, which align with the Earth's magnetic field and could pull on some kind of stretch receptor or hair-like cell as it changes polarity. The mineral has already been found in some bacteria, and in the noses of fish like salmon and rainbow trout, which also seem to track the Earth's magnetic field as they migrate.

Via Nicola Twilley

Image: Loggerhead Turtle, a Creative Commons Attribution (2.0) image from coda's photostream


    1. I’m glad someone has said this.  It’s a pet peeve of mine too, everything is “internal GPS” when usually what is meant is “internal map” or, as in this case something akin to a compass.

      Internal GPS != can navigate

  1. I saw something at Futility Closet a week or so ago on some oysters that were moved from the coast to a location inland, all in the dark.

    The oysters opened their shells twice a day, presumably for feeding, at the time of the high tide in their home beds in Long Island Sound. After two weeks, though, their timing shifted to follow the local tides in Evanston.

    Apparently they had recalibrated using the moon.

    Not having eyes, I assume they were able to detect the moon’s presence through its gravitational pull which, even if Bill O’Reilly doesn’t understand it, is how we get tides. So what else does nature have to teach us?

  2. It seems the “internal compass” people are at loggerheads with the “internal GPS” people.  

  3. I bet it’s present in mammals, too.  How else can cats and dogs find their way home from hundreds or thousands of miles away?

  4. Heinz Lowenstam and Joe Kerschvink were doing research on this stuff back in the ’80s — specifically, the biomineralization of magnetite.

    A lot of creatures, humans included, have magnetite crystals in cells within their brains.

  5. Seems like if this really were internal GPS they’d have a way to sense longitude in addition to latitude.

  6. Birds also have this sense, and it was discovered that they can ‘reset’ their compass with the rising sun.  This was important as the Earth’s field is by no means static, and indeed had repeatedly switched polarity.  I wonder how undersea creatures manage to overcome this.  It would also seem to suggest that it was a trait of a common ancestor.

  7. I have a little problem with the phrasing in your lead paragraph, that may be indicative of a larger problem endemic in science journalism–but you would be a far better judge of that than I.  Maybe the problem is all mine.  You mention “the fact that creatures like sea turtles can sense the Earth’s magnetic field”, but this is followed up in the quoted article with phrases like, “(t)hey seem to hatch with a set of directions”, “(w)hat isn’t known, however, is how they sense magnetism”, “many researchers think that magnetic receptors probably exist”, and “(t)hese might be based on crystals of magnetite”(all emphases mine). 

    There are a few more “might”s and possibilities mentioned, all of which would seem to point to a very believable theory, which, especially in the void of other theories, we might nudge toward fact-hood, in our hearts.  Granted, all the cited uncertainty pertains to the mechanism of this sense of magnetism, not the apparent certainty that turtles and other animals have that sense, to begin with (or that they seem to, anyway).

    Where my beef arises is in that there are other theories.  When we’re already talking about non-material fields, such as magnetism, can we easily discount other such fields, like behavioral fields?  I’m talking, specifically, about Rupert Sheldrake’s theory of morphic resonance, as described in his The Presence of the Past.  I know he’s somewhat poo-poo’d in orthodox science, and I’m just the sort of scientific half-wit that fails to understand why.  As I recall, that book wowed me with it’s opening sections on the history of science and the hazards presumption presents to scientific understanding.  It went on to describe the theory, and itemize the impacts that non-material fields appear to have on organisms, fields which may include morphic resonance, having a bearing on phenomena like animal migration, our experience of memories, the evolution of species, group behavior, and human learning.  Sheldrake’s whole career since then, seems dedicated to developing tests for the theory.

    Anyway, I found it fascinating.  Until we figure out how turtles find their way, I’m inclined to think, “could be morphic resonance”.  Until we figure out how memories are formed and/or stored, “could be morphic resonance”.  Flocks of birds all turning instantaneously on the fly, “could be morphic resonance”.  Until we figure out how magnets work…  Oh no wait, we have that one already, right?  Yeah, well, it’s another non-material field that we can see the effects of, perhaps more easily…  Maybe magnetism explains the rest, too…

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