Monitoring winter birds on the Mersea Harbour recharge beaches

Posted by Megan Jones, RSPB Old Hall Marshes Residential Volunteer, April 2026

On a breezy but sunny February morning we set out from West Mersea aboard Stacey Belbin’s boat Lady Grace to survey the Mersea Harbour Protection Trust (MHPT) recharge beaches in the Blackwater Estuary. The survey covered all four MHPT recharge sites: Cobmarsh Island, Packing Marsh Island, Old Hall Point and Tollesbury Wick.
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These shingle beaches were created using sand and gravel dredged from the approaches to Harwich Harbour as part of the Mersea Harbour and Tollesbury Wick Climate Change Adaptation Project completed in 2022, building on earlier recharge work carried out by the Environment Agency in the 1990s. As well as helping to protect the harbour and surrounding coastline from erosion and storm waves, the raised beaches also provide valuable habitat for wildlife, particularly high tide roosting areas for birds.

When the tide rises and the mudflats and marshes birds use for feeding become covered, they need somewhere safe to rest above the water until the tide falls again. Historically the Blackwater Estuary has had relatively few suitable high‑tide roost sites, something that is expected to become more of a challenge as sea levels rise. The recharge beaches help address this by creating raised areas where birds can gather and wait out the tide.

Bird surveys have been carried out since 2018 to monitor how birds use the recharge sites, and this survey was the final high‑tide roost count within the monitoring programme following the completion of the recharge works. Using the British Trust for Ornithology’s Wetland Bird Survey (WeBS) ‘look‑see’ method, we slowly travelled past each recharge area about an hour before high tide, counting birds through binoculars as we went while keeping a careful distance to avoid disturbing them.

We recorded a wide range of coastal bird species during the survey, with 940 birds counted in total. The most numerous were oystercatchers, with 358 counted across the sites, and dunlin, with 187 recorded. Many of the dunlin were gathered on the newer Tollesbury Wick recharge where large flocks were roosting on the shingle above the incoming tide. Oystercatchers were also widely spread, particularly on the newer recharge areas at Cobmarsh Island and Tollesbury Wick.

​One of the highlights of the morning was a single Purple Sandpiper roosting on the Tollesbury Wick recharge. Blending in amongst the Turnstones and Dunlin, it was easy to miss at first as it rested quietly on the shingle. Purple Sandpipers are hardy coastal wading birds more often associated with rocky shorelines, and they only appear along this stretch of the Essex coast occasionally, so this was a particularly memorable sighting.
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These surveys have helped build a clearer picture of how birds are using the recharge habitats and whether projects using the beneficial use of dredged sediment (BUDS) are delivering the intended benefits for wildlife. Monitoring the sites over time will also help inform future work in the estuary – including the new BUDS in the Blackwater Estuary project, which will build on the MHPT recharge work, continuing to use dredged sediment to help protect coastal habitats and communities while also creating valuable habitat for birds and other wildlife.