Aerial photo taken on April 27, 2022 shows Dongzhaigang National Nature Reserve, south China's Hainan Province. Dongzhaigang National Nature Reserve, the first wetland nature reserve dominating mangrove forest in China, started to conduct bird diversity monitoring in order to learn the changes and rules of bird population here. (Xinhua/Zhang Liyun)

Photo taken on April 27, 2022 shows mangrove seedlings at Dongzhaigang National Nature Reserve, south China's Hainan Province. Dongzhaigang National Nature Reserve, the first wetland nature reserve dominating mangrove forest in China, started to conduct bird diversity monitoring in order to learn the changes and rules of bird population here. (Xinhua/Zhang Liyun)

Aerial photo taken on April 27, 2022 shows Dongzhaigang National Nature Reserve, south China's Hainan Province. Dongzhaigang National Nature Reserve, the first wetland nature reserve dominating mangrove forest in China, started to conduct bird diversity monitoring in order to learn the changes and rules of bird population here. (Xinhua/Zhang Liyun)

Aerial photo taken on April 27, 2022 shows Dongzhaigang National Nature Reserve, south China's Hainan Province. Dongzhaigang National Nature Reserve, the first wetland nature reserve dominating mangrove forest in China, started to conduct bird diversity monitoring in order to learn the changes and rules of bird population here. (Xinhua/Zhang Liyun)

Photo taken on April 27, 2022 shows mangrove seedlings at Dongzhaigang National Nature Reserve, south China's Hainan Province. Dongzhaigang National Nature Reserve, the first wetland nature reserve dominating mangrove forest in China, started to conduct bird diversity monitoring in order to learn the changes and rules of bird population here. (Xinhua/Zhang Liyun)

Staff members and volunteers monitor birds at Dongzhaigang National Nature Reserve, south China's Hainan Province, April 27, 2022. Dongzhaigang National Nature Reserve, the first wetland nature reserve dominating mangrove forest in China, started to conduct bird diversity monitoring in order to learn the changes and rules of bird population here. (Xinhua/Zhang Liyun)

Photo taken on April 27, 2022 shows a black-winged stilt (Himantopus himantopus) at Dongzhaigang National Nature Reserve, south China's Hainan Province. Dongzhaigang National Nature Reserve, the first wetland nature reserve dominating mangrove forest in China, started to conduct bird diversity monitoring in order to learn the changes and rules of bird population here. (Xinhua/Zhang Liyun)

Aerial photo taken on April 27, 2022 shows Dongzhaigang National Nature Reserve, south China's Hainan Province. Dongzhaigang National Nature Reserve, the first wetland nature reserve dominating mangrove forest in China, started to conduct bird diversity monitoring in order to learn the changes and rules of bird population here. (Xinhua/Zhang Liyun)