Two additional nature preserves adjacent to the Chang Tang Reserve have put some 230,000 square miles (600,000 square kilometers) of the antelope's range under protection.
China has made chiru hunting illegal, and officials have collected many of the guns held in local communities, Schaller said.
Chinese authorities have also cracked down on poachers, stringing a net of backcountry patrols and roadside checkpoints to confiscate cars found with chiru hides, he said.
"Some chiru are still being killed and sent to India to make shahtoosh shawls, but the amount is way down from what it was even two or three years ago," Schaller told National Geographic News.
India and the international community have also clamped down on the shahtoosh trade, he noted.
Chiru have not recovered everywhere, however. In the eastern part of their range they have been essentially wiped out, the biologist said.
Schaller, who has studied the chiru since 1983, says scientists still have much to learn about the species (read a profile of George Schaller's lifetime achievements).
"The Chang Tang Reserve alone is bigger than the U.K. and about the size of Germany," he said, "and so you still don't know for sure where the animals all go to have their calves [or] where they migrate."
Schaller's recent expedition was co-sponsored by the National Geographic Society's Committee for Research and Exploration and WCS.
The team drove a small convoy of trucks and Land Cruisers across the northern Chang Tang, tracing a route last traveled in 1896 by two English army officers on horseback.
In addition to the chiru, the team found about a thousand of the region's native wild yak species, which is also highly endangered.
The yaks' rangeland is in decline from overgrazing by domestic yaks and sheep.
"Many families have left or been resettled by the government" because there's not enough grass to feed their herds, Schaller noted in the expedition report.
"Where once ten thousand domestic yaks grazed, only a thousand can now survive."
China promotes fence-building to restore the depleted grasslands. But local herders are fencing animals in rather than out, worsening the damage, the biologist says.
Schaller noted, however, that some nomadic communities living in the Chang Tang region have established local preserves to protect populations of wild yak and other wildlife.
"These wholly local Tibetan initiatives," he said in a media statement, "are the best means of establishing long-lasting conservation efforts, and they should be encouraged in every possible way."
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