"The minute you put up a fence you're going to face the issue of overgrazing like in the American West, and gazelles won't be able to migrate," Schaller said. "So careful planning is essential."
The Millennium Highway represents just one link in a proposed Asian highway network designed to promote tourism and trade. One preliminary plan calls for the route to traverse "a strictly protected area" called Nomrog in easternmost Mongolia.
Nomrog's mountainous topography and birch forests set it apart from anywhere else in the country. Schaller fears that opening up Nomrog to the superhighway would lead to similar intrusion into other national reserves.
An alternative route favored by conservationists would redirect the road through Choybalsan a provincial capital and the only major population center in eastern Mongoliathen snake just inside the Chinese-Mongolian border, avoiding pristine steppe grasslands along the way, and entering China before reaching Nomrog.
"This route would cause less environmental havoc," said Teter. "But I can't understand why a cash-strapped government would plan such a massive undertaking anyway, rather than upgrade the existing west-east road network which actually connects population centers."
To provide guidance for a route that sidesteps the timeless, trackless path of the gazelles, the researchers are studying the creatures' habitsand habitats.
Olson has been surveying 950 miles (1,500 kilometers) of transects of the steppe in spring and fall. "I cross dirt roads every now and then, muddy basins, and every 100 miles [160 kilometers] or so I come across nomads in their ger [the traditional round tent, also called a yurt]," he says.
"I drop in and say hello and explain what I'm doing. These guys are happy to tell you where they found gazelles or vice versa."
Olson, Schaller and their colleagues catch gazelles and collar them with mini-transmitters that operate for up to a year. So far they have tracked 100 gazelles and collected more than three years of data about their movements.
In the summer gazelles move northwest, and then reverse their path in late summer and fall. "But it's not cut-and-dry," Olson said. "The gazelles don't really stick to this." Another population of gazelles winters on the Russian border in the north and summers in the south.
"Gazelles need the entire area to keep their traditional travels," Schaller said.
The researchers aren't sure what influences the direction of migration. Olson is taking soil and vegetation samples to figure out what would draw the gazelles to a particular area.
"This is the time to protect and manage the eastern steppe as part of Mongolia's natural heritage for future generations," Olson said.
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