Effectiveness of a five-year project of intensive, regional-scale, coordinated management for little terns Sternula albifrons across the major UK colonies

Abstract

Little terns in the UK have undergone a population decline of 37 % over the last three decades despite protection efforts at their breeding sites during this time. In 2014, a five-year Little Tern Recovery Project was launched in the UK through the European Union LIFE + funding stream, deploying a more coordinated, comprehensive and strategic programme of conservation measures at 29 breeding sites across England and Wales. We compared little tern productivity (fledging probability per egg) during the project with that experienced in the five years prior to the project and included data from both project sites and reference sites. We found a positive relationship between productivity and colony size as well as differences in productivity between ‘northern’ and ‘southern’ regions of the UK, with colonies in the northern region doing better. There was a positive effect on productivity associated with the project’s enhanced measures, but this interacted negatively with colony size, such that increased productivity was only seen for colonies with ≤91 pairs (which comprised 90 % of our dataset). Although average modelled breeding success across all project sites during the project was low (0.37 chicks/pair), we found it was on average more than double (164 % increase) than it would have otherwise been in the absence of the enhanced management measures. For colonies with ≤91 pairs, the predicted increase was 208 %. However, for colonies >91 pairs, there was a predicted 20 % reduction in breeding success in the presence of enhanced management. This counter-intuitive result may be due to threats at larger sites already being managed as far as practicable prior to the project, and poor breeding success during the project being mainly due to stochastic, less manageable threats such as severe weather. In addition, fewer data were available to inform the model for larger colonies. Overall, we estimate that an additional 1,785 chicks fledged as a result of the project. Those that survive their first few years are expected to recruit back into the UK and Irish population, benefitting from the legacy of protection, habitat restoration and creation measures established as part of the project. However, a simple population model indicates that even if the elevated breeding success levels achieved by the project were maintained, the projected population decline between 2020–2050 would only be slowed by 30 %, so more needs to be done to achieve population stabilisation. However, the project’s beneficial impact has bought valuable time that can be used to further develop and deploy innovative solutions.