XINING -- A growing number of pregnant Tibetan antelopes are migrating to the heart of northwest China's Hoh Xil National Nature Reserve to give birth, according to the reserve's management bureau.

On Monday morning, a group of nearly 50 Tibetan antelopes was seen gathering by the side of the road at a section of the Qinghai-Tibet Highway. As a precautionary measure, the staff of the nature reserve implemented temporary traffic control to ensure safety.

Once the leading antelope carefully assessed the safety of the surroundings, the entire flock swiftly crossed the road and proceeded towards the vast hinterland of Hoh Xil.

Every year, tens of thousands of pregnant Tibetan antelopes start their migration to Hoh Xil in around May to give birth and leave with their offspring in late July.

"As weather conditions improved, there has been an uptick in the number of Tibetan antelopes crossing the highway to Zonag Lake in Hoh Xil," said Gyaom Dorge, a staffer with the Wudaoliang protection station of the Hoh Xil management bureau.

Over 1,000 Tibetan antelopes have traversed the vicinity near the station en route to Hoh Xil since this year's migration began on April 26, nine days earlier than last year.

Patrolling and monitoring along the migration route have been stepped up to ensure the species reach their breeding spots undisturbed.

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. Their population has increased over the past three decades thanks to the ban on illegal hunting and other measures implemented to improve its habitat.