Tern for the better

New research has shown that the growth of the Roseate Tern population on Coquet Island in Northumberland, the species’ only regular and reliable nesting site in the UK, has been supported for more than 20 years by birds moving from Rockabill in Ireland.

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The summer of 2018 saw record numbers of nesting Roseate Terns on Coquet Island, with more than half of the birds nesting there now home-grown. It’s now hoped the growing colony, and another thriving population at Lady’s Island Lake, Ireland, will also start to ‘export’ birds to found new colonies.

The authors of a paper just published in the Journal of Animal Ecology found that Ireland’s Rockabill colony, where 1,633 pairs of Roseate Terns nested this year, is the only site in the UK and Ireland currently ‘exporting’ terns to other colonies.

‘Cryptic sink’

The research, co-funded by the EU LIFE Programme, RSPB and Natural England, shows that for more than 20 years the growth of the Roseate Tern colony on Coquet Island was sustained by birds from the Rockabill colony. This meant Coquet was, between 1992 and 2016, a ‘cryptic sink’, attracting more young birds to nest there than have fledged from it and survived to breed at the species’ other colonies.

Co-author Dr Mark Bolton, from the RSPB’s Centre for Conservation Science, said: “Our research highlights the complex decisions conservationists face when deciding how to improve the fortunes of seabirds like Roseate Terns.

“Despite the reliance of the Coquet Island colony on immigration from Rockabill, this nature reserve has played an important role in maintaining the species in the UK, thanks to management by the RSPB, including building nest boxes and protecting the colony.

“Having an additional nesting colony, the UK and Irish population as a whole is better protected against catastrophes like severe weather events, disturbance or disease, that might hit any one colony.”

It’s hoped that the successful colony on Coquet will eventually contribute to Roseate Terns settling at new sites, or re-colonising some of their old haunts. Since the research was carried out, it appears that the Coquet Island Roseate Terns are now beginning to sustain their own numbers. In 2016, 50% of terns nesting on the island had been hatched there, but this year, the number had climbed to 60%. This summer, 118 pairs nested there, in the most successful UK breeding season in 40 years.

The RSPB’s Daniel Piec, who manages the EU Roseate Tern LIFE project, says: “With birds moving between colonies across borders, international co-operation is vital to their conservation. We’re working across Britain, Ireland and France with BirdWatch Ireland, National Parks and Wildlife Service, North Wales Wildlife Trust, Bretagne Vivante and other partners which means we are learning a great deal about what the terns need, and the areas they use.”

This shared knowledge will mean conservationists are better able to identify suitable sites to attract them to nest.

Co-author Dr Richard Caldow from Natural England says: “We now know that where coastal colonies of other tern species, such as Common Terns, are doing well and feeding predominantly in the marine environment, there is probably enough food and safe nesting areas for Roseate Terns to thrive there, too.

“The next step is to look for such potential nesting sites and consider ‘Coquet-style’ management to give Roseate Terns a helping hand to colonise them.”