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Endangered zebra life caught on GPS

  • Story Highlights
  • Princeton professor Daniel Rubenstein studies zebra behavior in Kenya
  • GPS collars enable biologists to study interactions between zebras
  • Research may help conservation of Grevy's zebra, which is endangered
  • The Grevy's zebra has a looser social network than the Plains zebra
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By Elizabeth Landau
CNN
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(CNN) -- If you were a zebra, how would you spend your days?

ZebraNet, a research project that began at Princeton, uses GPS collars to study the behavior of zebras.

Daniel Rubenstein, director of the Department of Ecology and Evolutionary Biology at Princeton University, has been pursuing this question for years.

He and collaborators spend their summers in Kenya trying to figure out how endangered zebras form social networks, avoid predators, and interact with the livestock and herders in the area.

ZebraNet, a collaborative project that Rubenstein co-founded with Princeton engineering professor Margaret Martonosi, studies zebra behavior through data from GPS locators on collars around zebras' necks. Photo See photos of ZebraNet in action »

Just like the positioning systems in cars, the collars collect information about the whereabouts of the zebras, as well as their velocities and turning angles.

The team is particularly interested in the Grevy's zebra, an endangered species whose numbers have dropped to only about 2,000. Data from the GPS collars have given Rubenstein and associates an unprecedented view of how Grevy's zebras balance the opportunities for acquiring food and water with the risks of being killed by lions.

The ability to gather data about nocturnal animals has always been limited, but with GPS collars recording data every eight minutes, the researchers learned a lot about zebra behavior at night.

The team, which includes several graduate students, found that zebras graze in the open plains during the day, moving slowly in straight lines, while lions rest under trees in wooded areas.

"They're like grass vacuum cleaners, chip-clipping away at the vegetation as they move," Rubenstein said of the zebras.

When night falls, the lions leave the woodlands to go hunting in the plains, and the zebras move into the woodlands, moving deliberately and quietly. They spend about 60 percent of the night in the woodlands, and the rest of the time in the plains, moving quickly and erratically while the lions hunt there.

"By using this remote sensing ability, we've been able to show the zebras change behavior markedly when they use the plains at night to minimize the risk of being preyed upon by lions," Rubenstein said.

In the past, when collared zebras got close to one another, ZebraNet's GPS technology transferred data between them. Eventually, all the data percolated back to the researchers' cars, which serve as mobile base stations. First getting information about interacting zebras was a thrill for Rubenstein.

"It was way cool to see the location and movements of many individuals from the data downloaded from only one!" he said.

Now, the project uses a similar technology that was recently developed by a German startup company. The new collars have improved battery power, but they don't have the peer-to-peer data swapping feature. They also sample every 15 minutes to an hour instead of every eight minutes, but can collect information over a longer period of time.

With these more power-efficient collars, researchers must track down each individual zebra and download its data. The second generation of these collars will debut this summer.

As a doctoral student at Duke University, Rubenstein was fascinated with how animals make decisions and why their societies form the way they do. He started studying equids -- a family of mammals that includes horses, donkeys, and zebras -- because they form associations among strangers.

He has also examined how the Grevy's zebra social network -- and he doesn't mean Facebook or MySpace -- may contribute to its endangerment. Associations between Grevy's zebras are less close-knit than those of the Plains zebra, whose core societies consist of closed-membership harem-groups and bachelor groups.

In a harem, several females choose to live with one male that protects them against harassment in exchange for sex. Female Grevy's zebras, on the other hand, don't stay with one male for long periods of time, meaning they don't have the benefit of a larger male watching out for them.

With food and water so scattered, female Grevy's zebras with young foals must stay near water to drink every day, while females without young foals wander more. Males, in turn, set up territories on access routes to water to gain mating opportunities with both the wandering females and ones that stay near water.

Lions, which prefer to eat Grevy's zebras, are a major source of endangerment as well. Rubenstein also plans to put collars on them to better understand their interactions with zebras and learn how best to intervene for the sake of zebra conservation.

ZebraNet also pays locals to gather data, which generates income for the communities, Rubenstein said. They put collars on livestock so researchers can examine the relationships between herds and herders, a topic that they will further investigate this summer.

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The project also increases awareness, as people come to understand that wildlife and livestock are not necessarily antagonistic.

"No longer are [zebras] necessarily vermin that are viewed negatively by the community," Rubenstein said. "They now have some economic worth." E-mail to a friend E-mail to a friend

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