JOHANNESBURG (AP) — At a time when mankind's encroachment on habitats is increasingly leading species to extinction, scientists have discovered a mass migration of animals in Africa that reaches farther than any other documented on the continent.

The journey made by about 2,000 zebra who traveled between Namibia and Botswana, two countries in a sparsely populated part of southern Africa, 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. Species of plants and animals around the planet are being wiped out at least 1,000 times faster than they did before humans arrived on the scene, said a separate study published Thursday by the journal Science.

The previously unheralded trek occurs within the Kavango-Zambezi Transfrontier Conservation Area, which 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, senior conservation scientist at the Washington-based World Wildlife Fund that led the two-year study on the migration. He said the main reason that the migration was not detected earlier was because it was impossible to know where the animals were going without GPS tracking technology, which has become more available and affordable in the last two decades.

The zebra odyssey encompasses a roundtrip journey of 500 kilometers (300 miles), starting in floodplains near the Namibia-Botswana border at the beginning of the wet season. It follows a route across the Chobe River and ends 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.

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

It wasn't until researchers put satellite tracking collars on eight zebras and monitored their movements in late 2012 and 2013 that the migration was discovered. 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, landed and affixed GPS collars, Naidoo said in an interview from Vancouver, Canada, where he is an adjunct professor specializing in the environment at the University of British Columbia.

David Wilcove, a conservation expert at Princeton University, described the migration as an extraordinary discovery at a time when such mass movements are dwindling.

"Even though people have been fascinated by animal migration since the dawn of history, we are just scratching the surface in terms of understanding which animals migrate, where they go, and how they do it," Wilcove, who was not involved in the research, wrote in an email.

Wildebeest in the Serengeti migration in East Africa meander, possibly covering more ground and certainly migrating in greater numbers than the zebra in Namibia and Botswana. But the southern African zebra move largely in a straight line and the distance between departure and destination points appears to be an average of 10 to 20 kilometers (6 to 12 miles) further than in the Serengeti, according to research cited by Naidoo.

Caribou in North America and Asia, Tibetan antelope and Mongolian gazelles are other animals that travel long migration routes. Other seasonal migrations of note include North America's Monarch butterflies, songbirds in the Americas and humpback whales in the Pacific Ocean.

Tony Sinclair, Naidoo's fellow academic 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" and 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," for example by hooking into 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.

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 and "whether this is genetically coded or passed behaviorally from mothers to offspring."

The zebras could have reached similar habitats closer to their starting point but instead 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."