Every March, sand martins from sub-Saharan Africa migrate to the inland UK to feed until September when they make their way back. Unfortunately, because there has been a decline of natural inland nest sites in the UK, the birds haven’t nested there for more than 25 years. That’s about to change thanks to an ambitious conservation project.

Led by the Surrey Wildlife Trust, the new project involves the construction of a 400-ton “sandcastle” to tempt the migrating birds back to a nature reserve in Surrey, South East England.

The structure, which aims to encourage sand martins to nest at the reserve, was built by professional sand sculptors who used a “giant bucket mold” made out of wooden boards.

The construction was the result of a partnership between Surrey Wildlife Trust and sand sculptors from Sand in Your Eye who built several test sandcastles in mid-January before starting work on the main construction in February. The 20-meter-long structure will allow hundreds of the tiny 12cm birds to nest and raise their young at the reserve.

In their nesting process, sand martins dig burrows of up to 90cm into the sand and make a small chamber at the end to lay their eggs in. Conservationists working on the project hope the initiative will enable the birds to roost together as well as help them find mates.

“Sand martin numbers have plummeted twice in the last 50 years as a result of droughts in their wintering grounds in Africa,” said James Herd, project manager at Surrey Wildlife Trust.

“In the UK, the natural nesting inland habitat along riverbanks has decreased as rivers pass through more urbanized areas and under roads, and quarrying has ceased,” said Herd. “So creating this nest bank is important to protect them against the boom and bust nature of their nesting sites and give more security for the population to expand.”