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Planet Earth

81. Longest Mammal Migration Tracked

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Humpback whales migrate farther than any other mammal, say researchers who tracked them along their more than 5,000-mile route. But why do they go so far? Although some believe the humpbacks do it to avoid killer whales, these scientists conclude that water temperature alone is what guides them.

Researchers at the Cascadia Research Collective in Olympia, Washington, tracked seven whales—which they recognized by the markings on their tail flukes—from their summer feeding grounds in the Antarctic Ocean to their winter breeding grounds off the Pacific coast of Central America. They also determined sea surface temperatures at similar breeding grounds all over the world, using satellite readings from the National Oceanographic Data Center.

The researchers found that humpbacks reproduce only in warm waters, 70 to 83 degrees Fahrenheit, regardless of latitude. Coastal upwelling in the Southern Hemisphere results in cool waters as far north as the equator in the Pacific, driving the whales all the way to Panama and Costa Rica for the southern winter.

The long journey, contrary to expectations, may actually end up conserving energy. Calves born in these warm waters, where they feed exclusively by nursing, can put their energy into growing rather than into keeping warm. This could make for larger adults that have more offspring.

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