The population of the endangered Tibetan antelopes in Tibet has expanded to about 150,000, a double increase from the late 1980s, according to a latest forestry survey report.

The survey, which lasted 18 years in Tibet, found the population of the rare animal has been growing at 7.9 percent annually over the past six years, in this southwest China autonomous region.

"Tibet currently has 149,930 Tibetan antelopes in a 698,000-sq-km area across 103 villages and 18 towns," said Liu Wulin, a research fellow at the regional forestry survey institute.

Tibetan antelopes are mostly found in Tibet, Qinghai Province and the western part of Xinjiang Uygur Autonomous Region. About 80 percent of China's Tibetan antelopes live in Qiangtang area of northern Tibet, which is home to about 70 percent of all the Tibetan antelopes worldwide.

The mating season for Tibetan antelopes lasts from November to January, and about 80,000 of the animals enter oestrum every year, said Liu.

"Their communities are polygamous," he said. "An adult male antelope has one to four mates on average."

Unlike many other animals, however, Tibetan antelopes are not prone to attack during their oestrum, he said. "When one of them seems aggressive, all the others will flee. So they rarely get injured amongst themselves."

Liu and his 118 colleagues have completed a report on the bioecology of Tibetan antelopes in Tibet at the end of their survey and used more precise scientific calculation devices to headcount the rare species.

"We have taken into consideration different factors that may affect the authenticity of the headcount, including the animal's mass seasonal migration and human activities," Liu told Xinhua in an interview Thursday.

The final calculation, he said, was based on the subtotals of Tibetan antelopes in every habitat, taking into account variables such as their population density in different seasons and different habitats.

Liu and his team have found in the survey that most Tibetan antelopes live in a vast area that expands from Nagqu Prefecture that borders Qinghai Province westward to the Gangdise Mountains and northward across the Hoh Xil, China's largest area of uninhabited land bordering Tibet, Qinghai and Xinjiang.

Forestry authorities said in 1989 there were more than 50,000 Tibetan antelopes in Tibet. The population was estimated to be at least 70,000 in 2000.

In Tibet there used to be several million Tibetan antelopes, but excessive poaching and human encroachment of their habitat caused their population to shrink sharply in the past decades.

International traffickers hunt the antelopes to make shahtoosh shawls, a luxury item that requires three to five pieces of antelope fur to make just one shawl.

Since 1979, the animal has been recognized as an endangered species and protected under the Convention on the International Trade in Endangered Species.

"Effective protection is the main reason for the Tibetan antelope population to expand," said Liu. "Until the mid 1990s, about 4,000 antelopes in Tibet were killed by illegal poachers a year. To date, illegal poaching has been curbed by at least 90 percent year-on-year."

Since 1998, Tibet has tightened supervision and patroling at the antelopes' habitats.

China has established three nature reserves to protect the rare creatures, covering a total of more than 600,000 sq km, an area 40 times the size of Beijing.

How to build the Qinghai-Tibet Railway, the world's most elevated railway that opened on July 1, through the homes of Tibetan antelopes was one of the biggest challenges confronting the railway designers and builders.

For the first time in any railway project, the Chinese government spent heavily to build 33 green passageways for animals.

Construction work was suspended for several consecutive nights when female antelopes crossed the site while migrating to and from their breeding site in June and August of 2003, when the Hoh Xil section of the railway was being built.

About 1,000 antelopes have crossed the railway via special passages so far, according to Gelai, an official with the Hoh Xil nature reserve administration.

The Tibetan antelope is also among the five doll mascots of the 2008 summer Olympiad to be held in Beijing.