Cemlyn Bay: A critical summer haven for some of our rarest seabirds
Each spring, as the days lengthen and seas begin to warm, thousands of seabirds end an extraordinary journey on Anglesey.
Flying north from the coasts of West Africa, they cross oceans and continents to return to the places where they were born. For many sandwich terns, that journey ends at Cemlyn Bay – a quiet shingle lagoon that plays an outsized role in their survival. Smaller numbers of Arctic terns also arrive here each year, completing one of the longest migrations in the natural world, travelling from their Antarctic wintering grounds to breed at Cemlyn Bay.
Cemlyn Bay, managed by the North Wales Wildlife Trust, is one of the most important seabird sites in Wales and the UK. Natural Resources Wales (NRW) contributes up to 50% of the annual management costs for the site, funding seasonal wardens, habitat management, predator control, monitoring and public engagement.
The site supports Wales’s only sandwich tern colony and the third largest in the UK. In recent years, around 1,500 pairs have returned to nest here – about 20% of the entire UK population and roughly 3% of the global population. For a single site, that makes Cemlyn exceptionally important.
Sandwich terns are striking birds. Mostly white, with a black cap, a black bill tipped with yellow and a deeply forked tail, they are unmistakable in flight. They are also long-lived and resilient, with some birds reaching their late twenties. Each year, they travel thousands of kilometres between UK breeding sites and wintering grounds in West Africa.
Arctic terns, though fewer in number at Cemlyn, are equally remarkable. They undertake an astonishing annual migration between the polar regions, travelling from Antarctic waters to Arctic breeding grounds and, for those nesting in the UK, to sites such as Cemlyn Bay. This epic round-trip journey, the longest known migration of any bird, highlights the global importance of safe, well-managed breeding habitats along their route.
The journey is perilous. Storms, food shortages and predators can all take their toll. That is why safe, well managed breeding sites like Cemlyn Bay are vital. In the UK, many important tern colonies only survive because they are protected within nature reserves.
Chris Wynne, Senior Reserves Manager, North Wales Wildlife Trust, said:
“The support from NRW is vital to safeguarding this internationally important seabird colony. It enables us to protect more than 2,000 Sandwich tern nests - one of the largest colonies in the UK. Following the first successful breeding of roseate terns here in three decades in 2025, we are hopeful they will return again in 2026.”
Cemlyn is not important in isolation. Terns are highly mobile seabirds that rely on a connected network of safe nesting sites. Alongside Y Skerries (Ynysoedd y Moelrhoniaid) and Ynys Feurig, Cemlyn forms part of the Anglesey Terns Special Protection Area.
Managing a site like Cemlyn takes ongoing effort. Since the Covid pandemic, visitor numbers have increased, bringing new challenges such as dogs off leads disturbing nesting areas. Wardens play a crucial role in protecting birds during the breeding season.
The colony has faced setbacks. In 2023, an outbreak of avian flu hit Cemlyn, and our officers supported the safe disposal of dead birds. Thanks to careful management, the colony has since recovered and returned to strong numbers.
Each year, these birds complete some of nature’s greatest journeys to reach Cemlyn Bay. Protecting this special place ensures they have somewhere safe to land – not just this year, but for generations of terns still to come.
Image: Arctic tern.