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Researchers Propose New Theory of Long-Distance Animal Navigation

Some members of the animal kingdom never venture far from home. Others, however, may migrate tens of thousands of kilometers, flying or swimming to distant destinations, and some of them - almost magically - return to the place of their birth, where they reproduce. Scientists are learning more about how animals perform these amazing feats of navigation, and as we hear from VOA's Art Chimes, the latest research is focusing on Earth's magnetic field.

Certain animals manage to find their way without benefit of map, compass or GPS. University of North Carolina professor Ken Lohmann says it fills him with "a sense of wonder."

"Animal navigation turns out to be remarkably complex," he says. "Animals that have been studied so far use more than one type of information. And in some cases, animals may draw upon even eight or more different types of information in the environment and use those interchangeably."

Information such as visual cues, the sun, smells and Earth's magnetic field.

The ability to use the magnetic environment - something we humans need a compass to exploit - is the topic of Lohmann's paper published this week in the Proceedings of the National Academy of Sciences. In the article, Lohmann and his colleagues propose a new theory about how certain animals they study - salmon and sea turtles - use magnetism to find their way across vast distances of open ocean and then return to where they were born.

"The idea that we propose is based on two findings. The first of these is that sea turtles and salmon are both able to sense the Earth's magnetic field. They both have well-developed magnetic senses," Lohmann says. "The second finding is that it turns out that different areas of coastline have associated with them slightly different magnetic fields."

Neither of these ideas individually is new, but Lohmann says his research team has put them together in a way that explains some amazing feats of animal navigation.

"And what we're proposing is that salmon and sea turtles, at the beginning of their lives, learn the magnetic field of their home area, and then retain this information as they migrate far away across thousands of kilometers of ocean, and finally, when it's time for them to return, they can exploit this information to help guide themselves back into the correct part of the world."

Lohmann stresses that he hasn't proved his theory, though he says it's the "first plausible explanation" of this kind of amazing animal navigation. Actually proving the theory would be challenging, in part because of the sea turtles' life cycle.

"The turtles take about 20 years to mature, and also only about one out of 4,000 or so young turtles actually survive to adulthood. But it might be possible to do this kind of a study with salmon."

Professor Lohmann says it's not clear exactly how the animals sense the magnetic field. One theory is that tiny particles of the magnetic mineral magnetite in the animals' brains may be acting as a kind of compass. The other involves some unusual chemistry in the vision process.

"So as an animal looks out at the world, it would see more or less everything that we see, but superimposed on that it would see a pattern of small lights or colors," Lohmann says. "So animals in effect could see the magnetic field or at least see a distinctive visual pattern when they face in different directions."

For salmon and sea turtles, magnetic navigation might not be the whole story. The Earth's magnetic field changes over time, and the magnetic signature a turtle remembers - somehow - from birth won't be the same when she returns to the same beach years later, but Lohmann says it would be close enough.

"These animals can potentially use the field to get back into the right general area. They would not be able to go directly to a highly-specific site, which is why we think that additional information has to be used at the end of the migration."

In the case of salmon, for example, they might be able to use the unique chemical signature or smell of a stream to identify it as the one where they were born.

Lohmann says with a better understanding of the process, it might be possible to exploit magnetic navigation for conservation purposes, for example by inducing salmon to spawn in rivers that have lost their native salmon population.