LONDON (AP) - It wasn't love. It could have been adventure. Or maybe she just got lost.
It remains a mystery why a female humpback whale swam thousands of miles from the reefs of Brazil to the African island of Madagascar, which researchers believe is the longest single trip ever undertaken by a mammal - humans excluded.
While humpbacks normally migrate along a north-to-south axis to feed and mate, this one - affectionately called AHWC No. 1363 - made the unusual decision to check out a new continent thousands of miles to the east.
Marine ecologist Peter Stevick says it probably wasn't love that motivated her - whales meet their partners at breeding sites, so it's unlikely that this one was following a potential mate.
"It may be that this is an extreme example of exploration," he said. "Or it could be that the animal got very lost."
Stevick laid out the details of the whale's trip on Wednesday in the Royal Society's Biology Letters, calculating that, at a minimum, the whale must have traveled about 6,200 miles to get from Brazil to Madagascar, off the coast of east Africa.
"No other mammal has been seen to move between two places that are further apart," said Stevick, who works at the Maine-based College of the Atlantic. And while he said "the distance alone would make it exceptional no matter where it had gone," there was an added element of interest.
Humpbacks are careful commuters, taking the same trip from cold waters where they hunt plankton, fish and krill to warm waters where they mingle and mate "year after year after year," he said. The location of their feeding and breeding spots sometimes varies, but their transoceanic commute doesn't usually change much.
Swapping a breeding ground in Brazil for one in Madagascar was previously unheard of.
"That's almost 90 degrees of longitude - so a quarter of the way around the globe," Stevick said. "Not only is this an exception, but it's a really remarkable exception at that."
Humpback whales are powerful swimmers, and the 40-ton behemoths typically clock up 5,000 miles in their trips from the frosty waters of the North Atlantic and the Antarctic to more temperate areas around the equator. They're known for their eerie songs - composed of moans and cries - which travel huge distances underwater and whose precise function remains a mystery.
They're also cherished by whale-watchers for their spectacular out-of-the-water jumps, called breaching.
Their numbers have recovered since they were almost hunted to extinction in the mid-20th century. But improvements have been uneven and scientists have been studying the whales and their movements to understand why.
It's to that end that Stevick and other experts have been trawling the Web for photos taken by tourists and whale-watchers, hoping to help build on a worldwide catalog of humpback whales which can be used to track where they travel.
It was by browsing photo-sharing site Flickr that one of Stevick's colleagues found a photo of this particular humpback, taken by a Norwegian tourist from a whale-watching vessel off the coast of Madagascar in 2001. The photo had been taken with a film camera and the negative sat undeveloped in a drawer for years. Eventually, it was scanned and posted to the Web, where it was spotted and added to the catalog.
Stevick's colleagues matched the Flickr photo to a picture of the whale taken two years earlier in Abrolhos, an area of small volcanic islands off the Brazilian coast.
So how did Stevick and his colleagues recognize the whale as the same one photographed by researchers in 1999? Carole Carlson, Stevick's colleague, said the key to identifying humpback whales is in their tails.
Humpbacks have big tail fins called "flukes," which are spotted and ridged. Carlson compared them to "huge fingerprints."
Stevick elaborated: "There's an enormous amount of information in those natural markings. There's the basic underlying pattern of the black and white pigment on it, numerous scars across the tail, and the edge is very jagged - each of those things provides a piece of information."
"The likelihood that two animals would have every single one of those things identical would be vanishingly small."
Simon Ingram, a professor of marine conservation at the University of Plymouth in southern England, expressed confidence the two photos showed the same whale, saying that photo identification was a "very, very powerful technique."
But Ingram, who wasn't involved in the research, said he was less excited by the length of the whale's trip than its destination.
"To my mind, the remarkable thing isn't the distance but the difference," he said. Whale communities were sometimes thought of as discrete communities, seldom mixing. This shows that's not always the case, he said.
As to why the whale went the way it did, Ingram said that, "the fact is, we just don't know.
"You can track them, but you don't know what's motivating them."