Metapopulation dynamics of roseate terns

Metapopulation dynamics of roseate terns: Sources, sinks and implications for conservation management decisions
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As part of the Roseate Tern LIFE project, we have analysed ringing and recovery data for the three main roseate tern colonies in NW European metapopulation i.e. Rockabill and Lady’s Island Lake in Republic of Ireland and Coquet in the UK. French colonies could not be included for the lack of sufficient data. The aim of the study was to determine which demographic parameters were responsible for the growth of the colonies.
 
The study, which was published late October 2018 in the Journal for Animal Ecology, was led by Adam Seward and Mark Bolton from RSPB Centre for Conservation Science and funded by EU LIFE Programme and Natural England.

Roseate Tern by Paul Morrison

Authors found that Ireland’s Rockabill colony, where 1,642 pairs of roseate terns nested this year, is the only site in the UK and Ireland which is currently effectively “exporting” roseate terns to other colonies and its growth has relied on good productivity and survival. On the other hand, for over 20 years the growth of the roseate tern colony on Coquet Island was sustained by birds from the Rockabill. This meant that Coquet Island 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.

Roseate terns on Rockabill by Brian Burke

​Despite the reliance of the Coquet Island colony on immigration from Rockabill, Coquet Island has played an important role in maintaining the species in the UK, achieving yet another record of 118 nesting pairs in 2018. 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. Moreover, 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, and this year the number had climbed to 60%.

Roseate tern terraces on Coquet Island by Paul Morrison

​Without demography data, it is tricky to choose and invest into sites, where roseate terns could eventually disperse to. 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. 

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Seward A, Ratcliffe N, Newton S, et al. Metapopulation dynamics of roseate terns: Sources, sinks and implications for conservation management decisions. J Anim Ecol. 2018;00:1–16.
https://doi. org/10.1111/1365-2656.12904