Humpback whales swim in amazingly straight lines during their seasonal migrations that cross thousands of miles of open ocean, and a new study says it's not clear how they're able to chart such a steady course.
"It's just absolutely remarkable how straight these courses are," says Travis Horton, an environmental scientist at the University of Canterbury in New Zealand, who studies animal migrations. "They're doing something rather precise. They're actively and deliberately navigating within some sort of external reference frame."
He worked with a team of biologists who have spent years tagging humpback whales near Brazil and tracking them as they migrate to Antarctic waters. The whales travel about 50 to 90 miles a day, says Alex Zerbini at the National Marine Mammal Laboratory, Alaska Fisheries Science Center in Seattle.
"You can look at the maps," says Zerbini, "and you see whales moving in a straight line for hundreds of kilometers."
They can do this despite storms and strong ocean currents that could potentially push them off track.
Horton says that decades of experiments on other migrating animals, like birds, suggested two possibilities for what the whales might be using to help navigate: the position of the sun or the Earth's magnetic field. He tested those ideas by analyzing both in relation to the whales' paths.
Neither strategy, on its own, could explain their movements, Horton and his colleagues report in the British journal Biology Letters.
"What we found is that the two leading theories of animal orientation don't necessarily work all that well for humpback whales," says Horton.
He thinks it is possible that the whales might be using a combination of the two strategies, "figuring out the position of the sun relative to the magnetic field or, vice versa, the magnetic field relative to the sun. To me, that's the best new theory as to how animals are migrating with such precision."
Patrick Robinson, a biologist at the University of California, Santa Cruz, says not many people study navigation in marine mammals. "Most of the work has been done on birds and other terrestrial animals," he says, adding that a lot of that work has been artificial experiments, not studies of creatures out in the wild.
"So it's very exciting to see additional work being done on the marine environment," says Robinson.
Robinson wasn't entirely surprised by the whales' navigation abilities, because he's recently been tracking the weeks-long migrations of northern elephant seals that travel from California out into middle of the North Pacific.
"And what's interesting is that we do have animals traveling in near-perfect straight lines, meaning a navigationally perfect straight line — a great circle route, which is different than simply following a straight compass bearing," says Robinson.
He says ocean dwellers clearly are expert navigators — and it will take a lot of scientific expertise to figure out how they do it. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.