Working staff measure the beak length of a crested tern at Jiushan island nature reserve in east China's Zhejiang Province, July 25, 2019. From July 24 to July 26, a total of 34 Chinese and U.S. seabird researchers and volunteers banded the crested terns in Jiushan island nature reserve to learn about the migration pattern of the birds, among which some are Chinese crested terns, the world's most endangered tern species. Nowadays the population of rare Chinese crested tern has exceeded 100. (Xinhua/Yin Xiaosheng)