A giant “sandcastle” has been constructed to encourage sand martins to nest at a nature reserve for the first time in 25 years, Surrey Wildlife Trust has said. The 400-tonne sand installation at Spynes Mere, near Merstham, Surrey, was built by professional sand sculptors who used a “giant bucket mould” made from wooden boards, as well as the help of diggers and dumper trucks. Sand martins visit the nature reserve when they migrate from sub-Saharan Africa each year, arriving from mid-March to feed until September, but they have not nested there for 25 years. The 20-metre--long construction will allow hundreds of the tiny 12cm birds to nest and raise their young at the reserve. Conservationists warn there has been a decrease in natural inland nest sites for sand martins, which dig burrows 50-90cm into the sand with their claws and make a small chamber at the end to lay their eggs in. It is hoped the scale of the scheme at the nature reserve will enable the sociable birds to roost together, and that the curved vertical face of the sandbank will allow them to peep out of the nest holes to find mates. James Herd, project manager at Surrey Wildlife Trust, said: “Sand martin numbers have plummeted twice in the last 50 years as a result of droughts in their wintering grounds in Africa. “In the UK, the natural nesting inland habitat along riverbanks has decreased as rivers pass through more urbanised areas and under roads, and quarrying has ceased,” he added. “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.” The structure, said Herd, would give the sand martins the chance to return to nest safely year after year at Spynes Mere, a part of the Nutfield Marshes that was originally created from a restored sand extraction site. To create the nest bank, in a method similar to using a bucket and spade on a beach, Surrey Wildlife Trust worked with sand sculptors from Sand in Your Eye to build several test sandcastles in mid-January before beginning the main construction in February. Jamie Wardley, a sand sculptor and the director of Sand in Your Eye, said: “We have only used sand from the site to create the structure from a giant bucket mould made from wooden boards. We added water to create the right mix, compacted the sand, and three to four weeks later the boards were removed. “The new ‘des res’ is ready for sand martins to move in, leaving nature and the sand martins to do the work of sculpting hundreds of nesting burrows.” The landowner, Sibelco, supported the conservation project by clearing the site of scrub and offered to supply extra personnel, diggers and dumper trucks for the build. Nick Allman, the site manager, said sand martins liked to nest in active extraction sites because of their fresh vertical sand faces, but if nesting birds were found it forced work to stop. “The sand martin bank is a way of naturally drawing them away from the active sites to where it is safer for them to nest,” he said. New vertical faces carved out at the site will provide 100 sq metres for sand martin homes, as well as a habitat for insects such as solitary wasps and bees, Surrey Wildlife Trust said. Up to a metre of the sandbanks will be shaved off the face annually to cut down on nest parasites; after five or six years, sand will be recycled to rebuild the bank so that it can provide a lasting home for the birds.