Yanchiwan National Nature Reserve, is a heaven for black-necked cranes, a national first-class protected species that lives in plateau regions.

The nature reserve in Northwest China's Gansu province, is located in the northern part of Qilian Mountain National Park. At the end of March, when Qilian Mountain ushers in an early spring thaw, the black-necked cranes will fly more than 2,000 kilometers back home, breaking the half year-long tranquility of the wetland.

The war for territory among black-necked cranes usually lasts for two months. For the sake of the next generation, their group solidarity disappears.

The length of their mating period is about half a month. During this time, their calls can be heard from time to time over a mountain that stretches for 800 km.

A month later, fledglings hatch out of the shells. Little cranes are hidden in the grass by their parents before they become familiar with the surrounding environment. The grass completely covers the little cranes' bodies, protecting them from danger.

In October, most migratory birds have to head south for the winter. The end of the month is their deadline. Every year, there are some cranes born so late that they can't fly south as others do, and end up freezing to death in the harsh winter.