New Field Could Explain How Salmon, Turtles, Find Home

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"What we're proposing is the sea turtles and salmon, when they begin life, basically learn, or imprint, on the magnetic field that marks their home area," Lohmann said.

"They retain this information. And years later, when it is time for them to return, they are able to exploit this information in navigating back to their home area."

Once the animals reach their native coastal areas, other senses, such as vision or smell, may guide them the rest of the way. Salmon, for example, are known to use smell to locate spawning grounds once the fish are nearby.

Lohmann and colleagues propose the theory in a paper published this week in a special package about movement ecology in the journal Proceedings of the National Academy of Sciences.

"We are excited about [the theory], because it really is the first plausible explanation for how sea turtles and salmon might be able to return," he said.

An Ancient Idea

Some 2,300 years ago, the Greek philosopher Aristotle searched for common features that unified animal movements of all types, noted Ran Nathan, an ecologist at the Hebrew University, Jerusalem.

This kicked off a long tradition of movement-ecology research.

But over the years, Nathan said, researchers have focused on different types of movement in specific species or landscapes, without looking at how different patterns impacted each other.

These scientists "never meet each other, they never talk to each other, they never go to the same conference, they publish in different journals," Nathan said.

In an effort to bring the scientific community together, Nathan led a yearlong project to establish a unifying framework for studying movement ecology.

Twelve teams of scientists were asked to address four basic questions: Why, how, where, and when do organisms move?

The methodology, Nathan said, applies to all types of organisms, from animals such as salmon, sea turtles, and elephants to bacteria and plants.

"If you give a legitimate field for the study of movement itself ... then people will study movement-related questions more thoroughly," Nathan said.

Martin Wikelski is a zoologist at the Max Planck Institute of Ornithology in Seewiesen, Germany, who specializes in animal movement.

The initiative to raise the prominence of movement ecology is "absolutely essential" to the understanding of wild animals, especially in an era complicated by a changing climate, Wikelski said.

"Every animal moves around and if we don't know the fate of these animals during movement, and how movement contributes to selection, then I think we are pretty much lost," he said.

For example, by understanding what animals encounter as they move about their environment, scientists may be able to determine the factors that cause some to go extinct.

Birds and Bees

James Mandel, an ecologist at Cornell University in Ithaca, New York, said the new paradigm is ideal for his research, which seeks connections between weather patterns and animal movement.

His team outfitted turkey vultures with GPS tags and two-way radio transmitters to collect data on the birds' hourly and daily movements.

One turkey vulture even carried a heart rate monitor to measure how much energy the bird expended during flight.

The researchers combined this data with information on the wind speed, atmospheric turbulence, and cloud height wherever the birds were.

The team found that turkey vultures soar from one billowing updraft of warm air to the next as they migrate thousands of miles between their summer and winter homes.

While many questions remain, Mandel said the data indicate the birds "are highly dependent on favorable weather conditions from energy source to energy source as they go."

Other teams applied the movement ecology framework to the study of elephants in Africa, elk in Canada, lynx in Spain, and butterflies from Estonia, Finland, and China.

Still other groups tested the methodology on seeds in Panama and various plants in the eastern U.S.

The Max Planck Institute's Wikelski, who is also a 2008 National Geographic emerging explorer (the National Geographic Society owns National Geographic News), is pioneering new tracking technology that allows scientists to study the movement of even the smallest creatures, such as bees.

(Related story: "Tiny Radio Tags Offer Rare Glimpse Into Bees' Universe" [November 14, 2008].)

The combination of Nathan's movement-ecology initiative and new technologies, he said, will open "a new era in biology."

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