Tens of thousands of birds, including rare and endangered species, flock each year to an unlikely haven sandwiched between high-rise Hong Kong and Shenzhen, the towering frontier of mainland China.
Up to 100,000 birds fly in from as far as Arctic Siberia and Central Asia to winter in marshes squeezed between the two urban giants, or to rest and fatten-up on their annual migration as far south as Australia and New Zealand.
But conservationists say this haven on the "East Asian-Australasian flyway" - one of the world's main migratory routes - is in danger of breaking up, as government and construction companies eye valuable land for development.
The birds descend on a 3,000 hectare (7,400 acre) strip of inter-tidal mudflats, mangrove swamps and traditional shrimp and fish ponds that stretch along the Hong Kong side of the Shenzhen river.
About half of the total area falls within the Mai Po and Inner Deep Bay nature reserve that is protected under an international treaty called the Ramsar convention.
The other half lies outside the reserve boundary.
"The area forms a continuous habitat. If any of the parts are lost, the whole system will be fragmented and isolated," says Hong Kong university ecology professor Billy Hau.
At least 10 species of globally endangered birds use this wetland zone, according to conservation group Birdlife International.
They include the striking blackfaced spoonbill, huge dalmatian pelicans and top predators such as imperial eagles that follow waterbirds for thousands of kilometres on their migration, preying on individuals along the way.
The unprotected section is in part of the Frontier Closed Area, established in the 1950s by the British former rulers of the territory, not for conservation purposes but as a buffer against mainland illegal immigrants.
The security measure kept the area isolated, effectively freezing development, and that was good for birds.
Now, more than a decade since Hong Kong's handover to China, while the border still remains the government is ready to open large swathes of the closed area as calls to develop the land get louder.
Among those hoping to profit are local landowners who have waited years to cash-in on their property, says Hau, as well as big construction firms poised to swoop on lucrative real-estate deals.
The government is conducting a joint study with global engineering giants ARUP with a view to creating a "combined conservation, eco-tourism and cross-boundary development zone" in the wetlands, according to Hong Kong's planning department.
"Low-density private residential or passive recreational development, in exchange for committed long-term conservation and management of the fish ponds or wetland may be permitted," Kenny Lau of the Planning Department told AFP.
This area "forms an integral part of the ecological system of Deep Bay and is worth preserving," he said.
The department says a balance will be achieved through a "public-private partnership," but conservationist Hau believes that the only way to protect the foraging grounds of endangered birds would be for the government to buy-out private landowners in the ecological corridor.
He isn't optimistic.
"Government will put NGOs and local landowners on a stage and allow them to fight it out so they can sit there and do nothing. They always do this," he told AFP.
In another part of the zone, separate from the Closed Area study, a 100-hectare wasteland called the Lok Ma Chau loop that almost bisects the marshes is slated for development.
Spoonbills, herons and raptors regularly fly across the patch, once a dumping ground for toxic mud dredged from the Shenzhen river, to reach fish ponds at the northern end of the wetlands.
Here the government, again with the help of ARUP, is studying plans to build a higher education and high-tech development zone, to be administered jointly with mainland authorities in a project hailed as a step towards Hong Kong's economic integration with mainland China.
"The loop is going to sever the north of the wetland from the south," Bena Smith, director of the WWF office that runs the Ramsar site told AFP.
Smith says the survival of all of Hong Kong's wetlands has become of international importance in the past decade because of rampant development elsewhere in Asia, including the destruction of thousands of hectares of bird habitats in mainland China, Taiwan and South Korea.
"Mai Po is one of the key spots on a regional network of wetlands that link to form the East Asian-Australasian flyway," he said.
ARUP declined to comment when contacted by AFP.
Access roads will cut the slim sliver of wetland that would remain on the southern edge of the loop, Mike Kilburn, vice-chairman of the Hong Kong bird watching society told AFP, adding that otters, leopard cats, civets, turtles and terrapins would also lose habitat.
Kilburn says that ecological realities are being lost in the hot air surrounding the development studies.
"A large bird, such a pelican, needs up to 500 metres to itself to feel secure," he told AFP.
"But you're just progressively shrinking the area and it's death by a thousand cuts. You do a cut here, a cut there, and suddenly you realise there's nothing left to protect."
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