Volunteer bird protectors monitor the Chinese crested terns of Jiushan Island, Xiangshan county, Zhejiang province. [Photo/chinabluenews WeChat]

Yu Xiaojian and Yan Zhiwen, two volunteer bird protectors, have spent years on Jiushan Island in Zhejiang province's Xiangshan county, closely monitoring the Chinese crested tern, which, with a total population of less than 100, is the world's most endangered tern species.

Once thought extinct, Chinese crested terns were spotted at Jiushan island in 2004, exciting bird lovers around the world.

Since 2013, 15 volunteer bird protectors have been recruited to the island to monitor and safeguard the rare bird, Yu and Yan among them.

Yu Xiaojian, a 61-year-old man responsible for documenting the birds on video, worked in wildlife protection at the Zhejiang Provincial Department of Forestry before his retirement.

"What fascinated me most was the word 'volunteer'; this means I am giving some of myself to the work for protecting the birds," Yu said.

Yan Zhiwen, Yu's 22-year-old partner, monitors and analyzes the migration habits of the birds.

Despite a rough environment, Jiushan Island feels like a paradise to the two volunteers, with their work making a great contribution to research into and protection of the endangered species.

More than 30 Chinese crested terns have been born recently at Jiushan Island, a third of the global population, thanks to the tireless efforts of their volunteer protectors.

Chinese crested terns perch on Jiushan Island, Xiangshan county, Zhejiang province. [Photo/chinabluenews WeChat]