Cemlyn Provides a Safe Haven

The tern colony at Cemlyn takes to the air. © Ben Stammers

The Cemlyn tern colony is currently at record numbers - a really wild spectacle. With recent local media coverage about the desertion of the Skerries tern colony, and the question “where have all the birds gone” , our latest blog draws on evidence we have collected and provides at least a partial answer to this question.

Cemlyn Lifeboat for Lighthouse terns

In answer to the question ‘Where have all the Skerries birds gone?’ We are very happy to report that approximately half these have come to Cemlyn – the closest alternative breeding habitat to the Skerries. Last year we had just 25 pairs Arctic and 10 pairs of common terns breeding at Cemlyn. This year the current figures are over 750 pairs of Arctic and at least 250 pairs of common tern, plus hundreds of loafing birds. A total of at least 2300 birds! We have also had sightings of Roseate tern, which like to nest alongside common terns and have similar habitat requirements. All this alongside what we think is now in excess of 2000 Sandwich tern nests.

The two low lying islands in the Cemlyn lagoon are currently looking ‘full’ and it is a truly awesome spectacle of a full-on breeding tern colony with chicks and activity happening at full pelt with constant movement and noise. The influx of these additional birds coincided with the abandonment of the Skerries colony. This circumstantial evidence that at least half of the Skerries birds have come to Cemlyn is borne out by the concrete evidence provided by reading the colour rings tagged on the legs of some of the Arctic and common terns recorded at Cemlyn by our wardens. At least 10 of these ring records confirm that these are indeed Skerries birds.

Skerries Lighthouse

The Skerries lighthouse off north-west Anglesey © Cemlyn wardens

Lighthouse terns

The Skerries, an island of the north-west coast of Anglesey, noted for its lighthouse, is also the UK’s largest colony of Arctic terns – last year it held 2,814 breeding pairs, with several hundred common terns also. The cause of abandonment this year appears to be due to disturbance and predation by peregrines combined with the absence of wardens as a result of the coronavirus lockdown. This serves to highlight how the wardening of tern colonies has become essential as the impact of man has reduced suitable habitat and increased disturbance levels.

But terns can adapt - their ability to be responsive, abandon and re-colonise when necessary is a valuable strategy.  So this does not mean a place will be abandoned for ever – as demonstrated at Cemlyn. In 2017 otter disturbance and predation caused the colony to abandon but look at it now; thanks to careful wardening and site management we now have a thriving colony back. What is important, however, is that alternative colonies are available and are managed in "gap" years. Maintaining this network of potential nesting sites has been an important part of the EU supported roseate tern LIFE project.

The Skerries has had its ups and downs in the past. First records of a tern colony on the Skerries in the 1890’s (when a lighthouse keeper shot four birds – possibly roseates!). A colony of 300 pairs of roseate terns was recorded at the Skerries in 1928. 

In between 1905 and 1935 there are records of an Arctic tern colony of a several thousand pairs on the Skerries (which declined to zero in the 1950s) but this has been thriving again in recent years.      

As desertion, re-colonisiation and adaptation to new sites are a feature of tern ecology, the availability of multiple breeding sites is essential – particularly in the face of a climate crisis with rising sea levels and changing ocean currents and their multiple impacts. The serious nature of the desertion of the Skerries this year can be in some way compensated for by the opportunity provided by Cemlyn and other sites around the Irish sea.

Although it is a disaster for the Skerries this year, much potentially can be learned to the benefit of future tern conservation by observing what happens this year. It has been fascinating to watch the story unfold at Cemlyn. Observing and counting the Sandwich terns nesting among the Black Headed gulls early in the season, then later in May witnessing the arrival of a handful of common and Arctic terns settle down to nest. Then suddenly this much later large influx which has changed everything.

Tern and chick

Arctic tern shelters it's chick © Cemlyn wardens

Finding their own space

The sound of the colony at Cemlyn is now completely different with the added calls of the common and Arctic terns – particularly the non-breeders which are so flighty and constantly ‘dreading.’ The distribution of the late nesting birds is also very interesting as they mingle in amongst the wandering Sandwich tern and black-headed gull chicks. The propensity of the Arctic terns to nest as far away from each other as possible within the safety of the colony can be seen as they space themselves out in the almost tundra-like conditions of the Cemlyn islands. Meanwhile the common terns gather around the nest boxes and among the slightly taller vegetation. But everything is now rammed in and there’s a lot of confusion as Sandwich terns fly in with food for their chicks. It will also be intriguing to find out where else the Arctic terns have gone.

Watch this space.

Lighthouses and Lifeboats - a historical footnote

The Skerries lighthouse was first lit in 1716 and constructed in its current form in the mid nineteenth century. It converted to automatic operation in 1987.  The Cemlyn lifeboat station, constructed in about 1828, was the first on Anglesey and closed in 1918. The buildings were demolished some time in the mid twentieth century. There is now a memorial stone and plinth on the location. 

Lifeboat memorial

Cemlyn lifeboat station memorial © NWWT

A helping hand

If you want to help us ensure that the terns have a future at Cemlyn – you can find out how here,