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There are, of course, any number of things that remain undiscovered, but one which, uh, I don't know, I've always felt rather overdue for discovery, is how animals have such a good sense of direction we keep hearing new stories about dogs going several hundred kilometers to find their homes, cats, too, sometimes, birds migrating, of course, fish, like salmon, finding their place of birth. Well, new research says that, for some of them anyway, it's all done with magnets, or at least the Earth's magnetic field. U.S. scientists say the fish remember a magnetic field indicating where they first entered the sea from a river. Nathan Patman is, uh, one of those scientists at Oregon State Univercity, who has been working on this. How did they establish that salmon rely on the magnetic field? / Oh, it took advantage of a, uh, serendipitous, uh, geological constraint. So, the Earth's magnetic field is not constant. It varies, uh, over the course of years and decades, and, it varies in, uh, a predictable sort of way. And, what we were able to do was to relate the gradual drift of the Earth's magnetic field to the, sort of, the gradual drift in the migratory routes that salmon were taking out in the open ocean to their home river. / 'Cause they always go back to the same river. That's the point. Do we ... / Yeah, that's the goal. / And you say, when the magnetic field changes, they may get one river out? They go to a next one up the coast? / Uh ... not quite. I mean, the Earth's magnetic field is ... is varying, you know, very subtly. It's not changing much. It's a great strategy for finding your home river even. What we did was to look at the Fraser River in British Columbia. It's like many other rivers, uh, the fish come out of the river, they go up to the sea, spend two years out there, and then they try to come back. But the catch is, when they try to come back to the Fraser river, Vancouver Island, some, you know, 350 or so kilometers obstacle, is blocking their direct access to the river. So, they have to make a detour around it. They have to go either to north or to the south. It's ... / Right. / ... essentially a two-choice test. It's a nice experiment, a natural experiment to see, you know, what is it about the northern route and the southern route that makes the most fish follow that as an entry way. / I see. And when the magnetic change ... field changes, they take a different decision? / Yeah. So, what happens is, when the magnetic field at the northern route is most similar to the magnetic field that they remembered from the Fraser River when they first went into the sea, more fish come in through the northern route. And ... / Wow. That's amazing, isn't it? / Yeah, and the converse is true for the southern, exactly. / How incredible. So, __ that's ... uh ... let ... let me just ask you this: Do other animals use the same thing? I mean, I don't think they do, because I'm looking at some research here. I mean, you / thought / they would all use magnets? / Not all, anyway. I mean, there is a lot that do, so I got my start looking at sea turtle navigation, and they seem to use __ the Earth magnet field to guide their way around, but, even salmon, I mean, they don't use the magnetic field entirely. It's sort of a question of scale. Once they get in the home river they start smelling their way. / If you put a magnet on ... on a turtle's back, would it make a mistake? / It depends on when and where and how you do it, but, uh, some research does indicate that turtles take more circuitous path when they have magnets on their heads. / So, now you know. And that was, uh, Nathan Patman, and it brings us to an end of this edition of Newshour. So, thank you very much for listening, and from Owen Bennett-Jones here in London. Good-bye.

Source : http://www.bbc.co.uk/podcasts/series/newshour newshour_20130207-2221a.mp3