JOHANNESBURG - At a time when mankind's encroachment on natural environments is increasingly a cause of extinction, scientists have discovered a mass migration of animals in Africa. The journey of 2,000 zebras reaches farther than any other documented on the continent.

The zebras travel between Namibia and Botswana, two countries in a sparsely populated part of southern Africa. It was discovered by wildlife experts only after some of the zebras were collared with tracking devices.

The newfound migration is a rare bright spot at a time when mass movements of wildlife are disappearing because of fencing, land occupation and other human pressures. A separate study published by the journal Science reported bad news: species of plants and animals are disappearing at least 1,000 times faster than they did before humans arrived on the scene.

Zebras Follow A Well-Traveled Route

The previously unnoticed trek occurs within the Kavango-Zambezi Transfrontier Conservation Area. This area is the size of Sweden and encompasses national parks in Namibia, Botswana, Zimbabwe, Zambia and Angola.

"It goes to show us that nature still has some surprises," said Robin Naidoo, a conservation scientist at the Washington-based World Wildlife Fund. His organization led the two-year study on the migration. Naidoo said the migration was not detected earlier mainly because it was impossible to know where the animals were going without GPS tracking technology. The technology has become more available and affordable in the last two decades.

The zebras travel a round-trip journey of 500 kilometers, or 300 miles. They start in floodplains near the Namibia-Botswana border at the beginning of the wet season. The animals follow a route across the Chobe River and end at the seasonally full waterholes and nutritional grass of Nxai Pan National Park in Botswana. The zebras spend about 10 weeks there before heading back.

The Secret Is Out

Local residents and conservationists knew the zebras left the Chobe River floodplains and returned months later in the dry season. Until recently, they didn't know where the animals went.

The migration was discovered when researchers put satellite tracking collars on eight zebras and monitored their movements in late 2012 and 2013. The findings were published this week in the conservation journal Oryx.

"This is the longest known land migration in Africa, in terms of distance between endpoints," Naidoo said.

To get the data in a "military-style operation," researchers fired tranquilizer darts at the zebras from a helicopter. Then they landed and attached GPS collars, Naidoo said. He is a professor specializing in the environment at the University of British Columbia.

David Wilcove, a conservation expert at Princeton University, was not involved in the research but still thought the finding was remarkable. He described the migration as an extraordinary discovery at a time when such mass movements are dwindling.

"We are just scratching the surface in terms of understanding which animals migrate, where they go, and how they do it," Wilcove wrote in an email.

Comparing Other Wanderers

Wildebeest in the Serengeti migration in East Africa are also known to wander. They possibly cover more ground and certainly migrate in greater numbers than these zebras.

The southern African zebras move largely in a straight line. The distance between their departure and destination points appears to be an average of 10 to 20 kilometers, or 6 to 12 miles, farther than the wildebeest travel, according to research described by Naidoo.

Caribou in North America and Asia, Tibetan antelope and Mongolian gazelles also travel long migration routes. Other seasonal migrations include North America's monarch butterflies, songbirds in the Americas and humpback whales in the Pacific Ocean.

Tony Sinclair, another professor at the University of British Columbia and an expert on the Serengeti migration, said the zebra research shows that the animals have to move through "human-dominated lands." He says that the migration could be lost if more protective measures are not put in place.

Sinclair wrote in an email that people whose land is traversed by the long migration route may obtain incentives to protect it "with some innovative thinking." One example may be linking to tourism.

In 2004, a fence that had blocked a zebra migration route since the late 1960s was removed in another part of Botswana. Some 15,000 zebras traveled the re-opened route in 2008-2009, according to research.

It Could Be An Ancient Trek

Much remains to be learned about the Namibia-Botswana migration. The World Wildlife Fund said long-term research is needed to confirm if the migration is annual and fixed. They also want to know "whether this is genetically coded or passed behaviorally from mothers to offspring."

The zebras could have reached similar habitats closer to their starting point. Instead they chose the longer trek, raising the possibility that they are following a pattern that is so ancient it has become embedded in their genes, according to the Oryx article.

Mike Chase, who leads Elephants Without Borders, a Botswana-based group that participated in the zebra migration study, said the trek stirs the heart.

"We all yearn for that, the romance of wild, open spaces," Chase said. "There are very few places left on our planet where animals and wildlife have the natural ability to roam in the context in which they evolved over thousands of years."