The city cluster in Guangdong province, an economic powerhouse in South China, has seen the rise of many urban wetlands, drawing large numbers of migratory birds and bird-loving citizens.
The provincial forestry bureau said the number of wetland parks in the Pearl River Delta, which houses one of China's super city clusters, rose to 123 by the end of 2018 from just three in 2012.
It means half of the province's wetland parks are now in this densely populated urban area, the bureau said. In China, wetlands are usually in the countryside or remote suburbs of cities.
In early May, several cities in the province are the sites of foraging waterside birds that are taking a rest in local wetland parks before continuing their seasonal migration.
In the Futian Mangrove Nature Reserve in Shenzhen, bird lovers can be seen training their cameras and telescopes on small waders meandering against the backdrop of high-rises.
As China's only national nature reserve located in a city, Futian has polished Shenzhen's fame as a paradise for migratory birds in recent years, officials said.
"Shenzhen has now become an important 'transit station' and 'gas station' for birds migrating on the Australia-Siberia route," said Wang Mengqi, deputy chief of the Futian administration for the nature reserve.
Guangdong launched a campaign in 2013 to conserve and restore wetlands around cities, and the improved wetland ecosystem has been credited for purifying rivers, mitigating the urban heat island effect and enhancing the region's appeal to investors.