An American expert attaches a collar to a crested tern in the Jiushan Archipelago National Nature Reserve on July 25. [Photo/Xinhua]

Thirty-four experts and volunteers from China and the United States attach collars onto the ankles of crested terns in the Jiushan Archipelago National Natural Reserve, Ningbo, from July 24 to 26.

The collars will allow the experts to study the migration of different groups of crested terns in order to better protect them, especially the Chinese crested terns.

The Chinese crested tern, a rare type of seabird, has been classified as critically endangered by BirdLife International, a global conservation organization that strives to protect birds.

The bird was first sighted in Indonesia in 1861 and disappeared after the 1940s. It was thought extinct by many bird experts. Fortunately, more than 60 years later, it was found again in China's coastal provinces of Zhejiang and Fujian.

In recent years, the bird's numbers have grown to over 100, according to the experts.