On April 2, a group of distinguished "guests" black-winged stilts came to the Yanhe River near the Lanjiaping Bridge in the urban area of Yan’an, which were seen flying and foraging for food, attracting many citizens to watch. It is known that this kind of bird typically inhabits fresh water and possesses high requirements for water quality. They breed in the Northeast, Northwest and North China. Their stopover in Yan'an during migration this time also witnessed the improvement of Yan'an's ecology.