"Once chiru became a fashion statement, the demand became so high it became a mass slaughter with organized teams and jeeps and automatic weapons just mowing the herds," Schaller said.
In addition to Ridgeway and Rowell, the expedition team included climbers Conrad Anker of Bozeman, Montana, and Jimmy Chin of Jackson, Wyoming.
Embarking last May, the mountaineers drove for five days from Llasa, Tibet, to Tose Kangiri, a 20,000-foot (6,100-meter) peak at the start of the chiru's 200-mile (320-kilometer) spring migration route.
The team covered the next 275 miles (440 kilometers) on foot, each pulling a 30-day supply of provisions in custom-built, two-wheeled aluminum rickshaws, across the trackless and often icy or muddy terrain.
"Each day was a slow burn of our bodies' reserve and an additional strain on our mental fortitude," Ridgeway said.
Aided by GPS units, Russian topographic maps, and Schaller's field notes, the expedition found a group of 70 female chiru on the sixth day of their trek.
For the next week, the team followed the antelope caravan until they reached the western herd's northern calving ground: a high plain where they observed two large groups of chiru, perhaps more than 4,000 animals.
For two days the team photographed and filmed the calving herduntil dwindling supplies forced them to move on.
Ridgeway said the expedition "filled my expectations, good and bad."
At the end of the month-long trek, Rowell, Ridgeway's friend for more than three decades, told him that the expedition had been among the "top two or three trips of his life."
"He said with more distance and reflection he anticipated it might be the best trip of life," Ridgeway said. "And I find some compromised satisfaction in that."
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