As the spring arrives, migratory birds are heading to their annual breeding grounds. The Chongming Dongtan National Nature Reserve in Shanghai, which is located in the middle of the East Asian-Australasian Flyway, is a major stopover point for migratory waterbirds making the long journey.

These wetlands on the eastern coast of Chongming Island are also home to the reserve's staff and research teams from Fudan University, who are busy banding birds, a decades-long task that involves attaching identification tags to the birds to track them and their routes.

"About 1 million visits by migratory birds — including those that fly past as well as stop over — are recorded at Dongtan every year," says Ma Zhijun, in his early 50s, a professor at Fudan University's School of Life Sciences, adding that an increasing number of waterbirds have been observed.

"We have been working together for more than 20 years. Through bird banding, we can better monitor the birds and carry out in-depth research on migration, getting to know more about them, conserving them, and protecting the whole ecosystem," Ma adds.

Zhao Yexi, 22, a doctoral student at Fudan University, says that bird banding involves fitting a small ring and a colored leg flag to a bird's leg. The ring is stamped or engraved with a unique code, and each colored flag represents a specific region.

The bands are usually loose enough to turn around the leg but not so loose they slip past the ankle. In addition, the banding process also involves identifying and recording each bird's basic information, such as species, age, sex, as well as morphological measurements of the length of wings and weight. The banding data is linked to the bird with its identification number. It is then registered on a database, and shared around the world for use in large-scale, long-term studies to track migratory movements, population dynamics, life span and behavior.

Newer technology also permits placing a positioning tracker on select birds, which allows researchers to precisely track the bird's continental, hemisphere-wide or even global movements.

"Bird banding is a common and effective means of monitoring the movement of birds, charting their migratory patterns, and supporting conservation," Zhao says.

"Over the past 20 years, more than 50,000 birds have been banded at the Chongming Dongtan reserve," Ma adds. "We are able to collect firsthand data and study their migratory routes, major stopover sites and timings. The data also helps us gain in-depth understanding, as well as new understanding of the natural history of migratory birds, and their link to the environment."