Sea-level rise is keeping exhausted migratory shorebirds flying round and round like aeroplanes in holding patterns, with nowhere to land and rest. The solution: artificial roosts fashioned from oyster bags…

Far Eastern Curlew (Endangered) resting on a floating roost © Chris Purnell

By Ding-Li Yong

The Geum Estuary, located on the coast of Seocheon, South Korea and abutting the Yellow Sea, is a crucial section of the East Asian-Australasian migratory flyway for birds. It regularly supports internationally significant populations of globally threatened shorebirds such as Spoon-billed Sandpiper Calidris pygmaea (Critically Endangered) and Far Eastern Curlew Numenius madagascariensis (Endangered). For this reason, it has been recognised as a Ramsar site (a wetland of international importance). However, along the Geum Estuary, as with other areas along this imperilled flyway, roosting sites for migratory shorebirds have been, and in some cases are still being, destroyed by coastal development and sea-level rise. Migratory shorebirds, which require these crucial roosting sites to rest during their long migration, are losing valuable habitat as a result.

Observing 10-15,000 shorebirds desperately circling the coast at high tide is a magical but disturbing sight,” says Chris Purnell, the Roost Trial Project Manager. “It’s like planes in a holding pattern: every moment they remain in the sky burns fuel they require to complete their onward journey.”

The optimal solution is to effectively manage, conserve, and if possible restore the natural roosting sites that are so crucial to these migratory birds. However, when that is impossible, one last-resort option is to try to build artificial roosting sites. Building these sites often involves significant construction and even possibly altering coastal ecology, but after seeing shorebirds roosting in infrastructure designed to support oyster aquaculture, BirdLife Australia came up with an idea: taking commercially-available oyster bags and turning them into floating roosts.

There are many advantages to floating roosts. They are not affected by sea-level rise caused by climate change, they do not become submerged when the tide changes, and they are even immune to terrestrial predators. But would the oyster bag floating roosts work? Tests were proposed in three different Ramsar sites in Australia, but it was the Geum Estuary that was considered the true proving ground.

An artificial roost in action at Geum Estuary © Chris Purnell

The Geum roosts were set up earlier this year, with oyster bags filled with locally-sourced empty shells that were towed out into coastal waters near the mudflats. Local staff kept an eye on the roosts to see if birds would begin to use them. The first sign of success came on May 8th, when around 28 shorebirds were recorded using the roosts, joined by another 15 when the tide receded. The next few days were much the same, with 35 shorebirds arriving at high tide, and a handful more as the tide ebbed. By the end of May the true potential of the roosts could be seen, as footage captured the roosts with nearly 300 birds using them.

As the project moves forwards, we will continue to monitor the roosts to see if these hopeful beginnings are signs of a long-term trend. With the southern migration now underway, the biggest question is whether birds will use the roosts on their journey down to Australia. In 2020 results of the trial will be reviewed to determine whether to remove, adapt or extend the trial. The teams are also studying the use of traditional craft materials created by indigenous communities to form the roosts, in order to reduce the use of plastics and support heritage and local economies.

We are optimistic that the roost trials in both Korea and Australia will be extended with the successful results from the initial trials,” says Young-Min Moon, project coordinator for BirdLife Asia. “We are already hearing that some local governments and stakeholders are interested after seeing that the roost trials have worked very well for shorebirds.”