Photo taken on April 26, 2020 shows relict gulls (larus relictus) in a national wetland park in Kangbao County, north China's Hebei Province. Every year, over 7,000 relict gulls, which is under first-class state protection, fly to the wetland park. (Xinhua/Yang Shiyao)

Photo taken on April 26, 2020 shows relict gulls (larus relictus) flying in a national wetland park in Kangbao County, north China's Hebei Province. Every year, over 7,000 relict gulls, which is under first-class state protection, fly to the wetland park. (Xinhua/Yang Shiyao)

Photo taken on April 26, 2020 shows relict gulls (larus relictus) flying in a national wetland park in Kangbao County, north China's Hebei Province. Every year, over 7,000 relict gulls, which is under first-class state protection, fly to the wetland park. (Xinhua/Yang Shiyao)

Photo taken on April 26, 2020 shows relict gulls (larus relictus) in a national wetland park in Kangbao County, north China's Hebei Province. Every year, over 7,000 relict gulls, which is under first-class state protection, fly to the wetland park. (Xinhua/Yang Shiyao)

Photo taken on April 26, 2020 shows a relict gull (larus relictus) flying in a national wetland park in Kangbao County, north China's Hebei Province. Every year, over 7,000 relict gulls, which is under first-class state protection, fly to the wetland park. (Xinhua/Yang Shiyao)

Photo taken on April 26, 2020 shows relict gulls (larus relictus) flying in a national wetland park in Kangbao County, north China's Hebei Province. Every year, over 7,000 relict gulls, which is under first-class state protection, fly to the wetland park. (Xinhua/Yang Shiyao)