XINING - Pregnant Tibetan antelopes have begun their annual migration to the heart of Northwest China's Hoh Xil National Nature Reserve to give birth, the reserve's management bureau said Monday.

A video clip released by the bureau showed that the first group of 235 Tibetan antelopes passed the Qinghai-Tibet Highway via a special passage for animals on Sunday afternoon en route to Zonag Lake and other breeding areas in Hoh Xil.

Protection stations have been set up along the migration route, and measures such as temporary traffic control, prohibition on honking and patrolling have been put in place to ensure the species reach their breeding spots undisturbed.

Every year, tens of thousands of pregnant Tibetan antelopes start their migration to Hoh Xil in May to give birth after mating in November or December, and leave with their offspring in around August.

Under the first-class state protection in China, the once-endangered species is mostly found in Tibet autonomous region, Qinghai province, and Xinjiang Uygur autonomous region. It plays a key role in maintaining the ecological balance on the Qinghai-Tibet Plateau.

The population of the Tibetan antelope has increased over the past three decades thanks to the ban on illegal hunting and other measures to improve its habitat.

According to statistics from the National Forestry and Grassland Administration, the population of the species has grown from 60,000 to 70,000 in the early 1990s to around 300,000 now.