Editor's note: As protection of the planet's flora, fauna and resources becomes increasingly important, China Daily is publishing a series of stories to illustrate the country's commitment to safeguarding the natural world.

July is not only one of the busiest times of year for wildlife rangers on the Qinghai-Tibet Plateau, but also a time of great care and responsibility. Here, rangers and researchers at the Xizang Changtang National Nature Reserve, located at an altitude of 5,000 meters above sea level, observe and monitor the mass migration of Tibetan antelopes.

Some 150,000 Tibetan antelopes, also known as chiru, live high up on the plateau and migrate from Qinghai province to the Changtang reserve to birth their young.

The species used to be listed as endangered due in part to them being hunted for their fur, but years of conservation work has lifted their number and they are now classified as near threatened by the International Union for the Conservation of Nature.

This year, the wildlife rangers have been joined by a team of photographers and filmmakers to document the migration, typically ranging from several hundred kilometers to about 1,000 km, across what is known by many as the "roof of the world".

Starting from a patrol station in Rungma township, documentary filmmaker Zhang Lina and two photographers, Guo Peng and Xu Qianbo, ride by motorcycle across hills and streams for 3 hours to catch up with the migrating herds.

"Although the flow of the rivers along the way is not particularly strong, the river channels are deep and long. Adult Tibetan antelopes can generally leap over easily, but young ones are at high risk of being swept away by the currents and drowning," Zhang said.

"The rangers wait downstream to try and rescue them."