HONG KONG — Squeezed tightly between two megacities with a combined population of 20 million are some of East Asia’s most important wetlands, where rare birds sing out amid traditional shrimp ponds.

Look up, and looming right above this rustic setting are the crush of skyscrapers in Shenzhen, China, almost close enough to touch. Just out of view behind some hills to the south are the congested streets of Kowloon and Hong Kong Island.

But in this corner of northwest Hong Kong, tens of thousands of cormorants, herons, egrets, sandpipers and other birds, including endangered species like the black-faced spoonbill, gather each winter to feed on the mud flats. Eucalyptus trees line a path that cuts along the shrimp and fishponds, where small restaurants serve up the day’s harvest.