Sandwiches arrive late for Cemlyn’s Picnic!

Terns at Cemlyn Nature Reserve

No matter how well you think you might know a place and its wildlife, there are always surprises! This year, the terns of Cemlyn have really kept us guessing. Alison Brown, Roseate Tern LIFE Project Engagement Officer, gives an update on the remarkable changes in fortune at Cemlyn’s tern colony.

It was once said that if you ‘buy a Sandwich tern colony and make it into a nature reserve … they will probably repay you by nesting somewhere else the following year’.  Rob Hume’s comments were telling.  Between 2012 and 2016, the average breeding population of Sandwich terns at Cemlyn was 2400 pairs of adult birds, raising nearly 1000 chicks each year.  These Cemlyn Sandwiches are, or were, 20% of the UK population for Sandwich terns and 3% of the whole world population.  They were also the only Sandwich tern colony in Wales.  This springtime, however, Cemlyn was relatively peaceful and the loud, discordant calls of ‘ERIC’ which normally announce the arrival of summer to northern Anglesey were quieter than usual.  What happened?

Visit Cemlyn Nature reserve to see Terns for yourself

Sandwich terns are the largest and heaviest of the British breeding species of terns but are, despite their size, fairly timid when defending their nests and react strongly to disturbance, predation and, it would seem to human eyes, mere whim.

In 2017, the fast growth of the Sandwich tern colony at Cemlyn raised concerns that there might be competition for nesting space with Cemlyn’s other species of terns.  Artificial rafts were put into place on Cemlyn’s lagoon to provide ‘overspill’ nesting sites for any common and Arctic terns displaced by their larger cousins.  However, as it turned out, the additional nesting sites were not needed.  The summer of 2017 saw a complete break in Sandwich tern nesting, due (mostly) to predation and disturbance by a family of otters (and other species ).  Breeding failed and, by early June of 2017, all the adult Sandwich terns dispersed away from Cemlyn and northern Anglesey without raising young.

Cemlyn is part of a European network of sites for birds and wildlife habitats; the Natura 2000 network.   Each of these sites has a bespoke management plan aimed at protecting, conserving and building resilience for wildlife and natural habitats.  For Cemlyn, the statutory management plan includes specific goals of providing nesting habitat for terns, whether or not they are present.  In early 2018, in accordance with this management plan and the long-term international goals of tern protection and management, North Wales Wildlife Trust undertook a number of projects including building climate change resilience, ‘predator-proofing’ for nesting habitats and non-lethal control of predators.  This work was funded through the LIFE Programme of the European Union and the project ‘improving the conservation prospects of the priority species, the Roseate Tern, throughout its range in the UK and Ireland’.

Despite these efforts and the creation of new and safer nesting habitat, 2018 has again been a truly remarkable year – but for the wrong reasons.  This springtime, Sandwich terns returned to Cemlyn in much lower numbers than in 2017 and we were not quite sure where these truly beautiful birds with the dreadful screechy voices might have gone, although Hodbarrow in Cumbria had a bumper start to the year. There are many factors that influence tern distribution and breeding success, not least being changing climate and weather around their breeding grounds in north-western Europe but also in their over-wintering territories in West Africa.

The late winter of 2017-18 saw the arrival of the so called ‘Beast from the East’, a prolonged period of extreme cold across the UK.  Whilst this cold would not have directly affected Sandwich terns that, at the time, would have still been in their winter quarters around the coasts of West Africa, the extreme cold and prevalence of northerly and easterly winds may have affected their northward migration as well as sea temperatures and fish distribution.  Terns arriving in the UK after long and arduous migrations rely on sand eels to ‘refuel’ before breeding, present to their mates as incentives to breeding and, ultimately, to feed young chicks.  In the spring of 2018, north-easterly winds continued to dominate weather patterns and informal discussions with sea anglers and charter boat fishermen around Anglesey’s coasts reported an absence of sand eels in coastal areas as well as unusually cold water temperatures in April and May.  As the summer progresses, the sand eels and small fish which form the basis of the terns’ feeding will return – however, it may be too late to encourage large numbers of Sandwich Terns to settle and breed at Cemlyn this year.

It is true that predator disturbance in 2017 probably led to the abandonment of nesting by all the three tern species which come to Cemlyn. However, it would be simplistic to suggest that this predation had ‘caused’ the Sandwich terns to initially avoid the site this year.  North Wales Wildlife Trust have undertaken substantial works to deter predators and our summer wardens, Tim and Tarik, have reported that no otters have been seen on the lagoon islands this spring.  Despite the troubles of 2017, Cemlyn still attracted Sandwich, common and Arctic terns.  In early June, a count indicated some 300 Sandwich Terns nests – 10% of previous years’ counts.  However, the return and presence of terns and black-headed gulls to Cemlyn in the spring reassured us that the Cemlyn site, with its new and improved and ‘safer’ nesting habitat, is a worthwhile place to breed and raise young.

The weather in 2018 has been, to put it mildly, unpredictable.  On 14 June, the west coast of the UK bore the brunt of Storm Hector and, the further north you were that day, the worse the wind.  On 18 and 19 June, Cemlyn received an influx of about 500 adult Sandwich Terns.  The end of June has seen similarly unusual weather with very high temperatures and a pronounced lack of rain, especially in the north and west.  On 30 June, another 200 or so Sandwich terns arrived at Cemlyn.  These new birds take the overall estimate for Sandwich terns up to 1500 to 1800 and many of the late arrivals appear to be making an ambitious attempt to breed!

Better late than never!