Where did the zebras go? Epic migration may be in their DNA

Martin Harvey/WWF-Canon

The migration routes that animals follow might be genetically coded, according to a new study.

World Wildlife Fund researchers tracked the migration of adult female zebras from a conservancy along the Chobe River floodplains in 2012 and 2013. They were interested, study lead Robin Naidoo told CBS News in a phone call, because "the zebras were arriving in the dry season, hanging out for a few months and then disappearing." The researchers wanted to know where the zebras were moving when they left this communal conservancy.

The first time, they tracked the migration of eight adult females that started moving south on December 3, 2012. Most reached the destination by December 27, with the final zebra arriving in the Nxai Pan area on January 9, 2013. An aerial survey of the pan indicated that more than 1,500 zebras make the trek.

The zebras were tracked by GPS collars worn around their necks.
Robin Naidoo/WWF

The animals were much more leisurely in the return trip to the Chobe River floodplains, covering the trip in about 85 days (compared to the average 15-day journey south). They took a much more circuitous route back, covering more than 400 miles. The round-trip journey is about 590 miles, the longest known overland migration in Africa.

The researchers were "really stunned to discover the length of the migration," Naidoo added. "It's not every day that you discover a migration that's among the longest, if not the longest... No one expected a movement like this to be happening."

A year later, all of the surviving zebras made the same migration. It's especially amazing, Naidoo said, that "something as large and well understood as a zebra could be making this kind of migration right under people's noses."

Understanding the length of the migration was only the first step. Now, they're looking to determine why they follow this pattern. One likely reason is access to water. Zebras need to drink water daily. In the dry season, this means they need to be near rivers and floodplains. In the rainy season, they can choose where to go.

When they embarked on the study, the researchers expected that the area where the zebras migrated would be "significantly different" to sites that the zebras passed en route. Interestingly, the zebras bypassed several environmentally similar areas before arriving at their destination. If water was the only catalyst, they could have accessed it without traveling so far.

The migrations will have to be tracked for several years before conclusions can be drawn regarding the relationship between rainfall and migration, but the timing indicated that it has more to do with the amount of rainfall in the destination -- not the origin.

"The fact that they seemed to be responding to [a weather event] that was quite far away was suggestive," said Naidoo. "Previous studies showed that zebras are able to orient to environmental cues that are really far away from where they actually are. We need to track this over subsequent years to see consistency."

There could be an explanation much more interesting than access to water: the migratory patterns may be genetically coded.

Previous research has shown that even after years of interruption, animals will return to historic migration patterns when given the opportunity. For as long as researchers tracked migration, about 15,000 zebras in Botswana followed a long-distance migration pattern each year. They only stopped when a fence blocked their way starting in 1964. When the fence was removed more than 40 years later, they remarkably returned to the long-distance migration pattern previous generations followed decades earlier, according to research conducted in 2008. "This completely separate migration suggests conserved memory of an ancient route that may be genetically encoded," Naidoo wrote.

Additional evidence comes from the patterns followed by pronghorn antelope in the American Grand Teton National Park. The routes have not changed since the Holocene era some 12,000 years ago.

The authors conclude that the evidence supports the need for prioritizing conservation efforts. The full distance of the migration is within the proposed Kavango-Zambezi Transfrontier Conservation Area, an international area that covers parts of Namibia, Botswana, Angola, Zambia and Zimbabwe. The area is about the size of Sweden. Making it a protected zone will help the animals as well as the locals, as it will increase tourism opportunities, he noted.

The fact that such a lengthy migration went unnoticed indicates that there could be others, and measures need to be taken to preserve these natural phenomena. Longer migrations are known to have existed in the past, but they are now extinguished due to human intervention and land use.

"We're losing these things all around the world, so to find a new one brings home the point that we need to conserve these types of things," said Naidoo.

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    Danielle Elliot is a freelance science editor and reporter for CBS News. She holds an M.A. in science and health journalism from Columbia University and a B.A. in broadcast journalism from the University of Maryland. Follow her on Twitter - @daniellelliot.