Photo taken on March 31, 2020 shows migrant birds at the Wolong Lake wetland in Kangping County of Shenyang, capital of northeast China's Liaoning Province. (Xinhua/Long Lei)

Photo taken on March 31, 2020 shows migrant birds at the Wolong Lake wetland in Kangping County of Shenyang, capital of northeast China's Liaoning Province. (Xinhua/Long Lei)

Photo taken on March 31, 2020 shows migrant birds at the Wolong Lake wetland in Kangping County of Shenyang, capital of northeast China's Liaoning Province. (Xinhua/Long Lei)

Photo taken on March 31, 2020 shows migrant birds at the Wolong Lake wetland in Kangping County of Shenyang, capital of northeast China's Liaoning Province. (Xinhua/Long Lei)

Photo taken on March 31, 2020 shows migrant birds at the Wolong Lake wetland in Kangping County of Shenyang, capital of northeast China's Liaoning Province. (Xinhua/Long Lei)