LANZHOU, Feb. 21 (Xinhua) -- A migratory whooper swan wearing an identification collar was spotted for the first time in Lanzhou, capital of northwest China's Gansu Province, where dozens of such birds are wintering.

Last week, researchers discovered that the number of wintering whooper swans at a habitat on the local section of the Yellow River has slightly increased from 17 a year ago to 23. After days of observation, they found that one of the birds has a blue collar with the serial number "1T83" on its neck and it had arrived with its family.

"This was the first time for us to see a banded whooper swan inhabiting Lanzhou," said Zhang Zhe, who works with the local forestry bureau.

Bird banding is a common practice for identifying individual birds and monitoring their migration, population, distribution, and levels of environmental pollutants, among other information, to provide a scientific basis for protecting endangered species and preventing bird flu, said Zhang Lixun, head of the wildlife biodiversity monitoring and protection team from Lanzhou University.

He said "1T83" was among over 100 swans banded and then released in western Mongolia in 2011. The bird was spotted in Gansu's neighboring province of Qinghai in December 2021, indicating that its wintering site is not fixed.

The "1T83" family is expected to leave Gansu by the end of February, according to experts. The local forestry bureau will continue monitoring and data reporting.

Gansu is located on two international bird migration routes, which are from Central Asia to India and from East Asia to Australia. With the onset of autumn, a good number of migratory birds fly to Gansu and stay till the end of winter.