Review of approaches and development of a decision framework for SPA boundary extensions in the UK MIKETOMS Fri, 14/08/2026 - 08:31

Feather, A., Woodward, I.D., Burton, N.H.K., Frost, T.M. & Bowgen, K.M.

rr-817-feather-et-al-spas-final.pdf

Special Protection Areas (SPAs) protect rare, vulnerable and migratory birds, together with the habitats on which they depend. Many of these birds also rely on areas located outside SPA boundaries, using these for feeding, roosting and refuge. Such areas, referred to as Functionally Linked Land, may be essential to maintaining the bird populations for which SPAs were designated.

This report reviews methods for identifying Functionally Linked Land, particularly for non-breeding waterbirds, and considers how these could inform future SPA boundary extensions. Existing approaches range from simple thresholds to predictive modelling and analyses of bird movements. Although these methods can identify important supporting habitats, differences in definitions, data quality and analytical complexity limit consistency and comparability.

The report proposes a structured decision-support framework, based on connectivity, abundance and frequency of use, categorising areas as ‘core’, ‘primary support’ or ‘secondary support’. This approach provides a transparent basis for prioritising areas for potential inclusion, while recognising that ecological evidence must be considered alongside proportionality, practicality and policy context.

The framework could strengthen UK conservation policy by making decisions on SPA boundaries more evidence-based, consistent and reproducible. The work promotes a more connected and adaptable approach to protected-site management.

Special Protection Areas (SPAs) are sites classified under UK law to protect essential habitats (i.e. breeding, wintering) for rare, vulnerable and migratory bird species. Some habitats (e.g. agricultural), however, are frequently located outside existing boundaries despite the crucial resources they provide (e.g. feeding, roosting) for the species for which SPAs were designated. These areas are referred to as Functionally Linked Land (FLL), defined as habitat outside a site boundary that supports populations for which the site was classified. This report reviews current approaches for identifying FLL, which may assist with developing an approach to inform SPA boundary extensions in the UK, specifically where these areas comprise habitats that are important for non-breeding waterbirds. The review synthesises methodologies from recent studies; approaches range from threshold-based classifications to predictive modelling using environmental variables and connectivity analyses informed by movement data. While these methods successfully identify key supporting habitats, they vary in complexity and consistency, creating challenges for comparability and scalability.

Strengths of current approaches include flexibility, integration of multiple data sources (e.g. structured long-term monitoring schemes, unstructured citizen science records, expert knowledge), and predictive capability through statistical models. Some studies incorporate connectivity metrics using tracking data or coordinated visual surveys, thereby providing a better description of ecological networks. Limitations include reliance on incomplete or biased datasets, inconsistent definitions, and limited empirical evidence of connectivity. Gaps in nocturnal data and biases in citizen science reporting create further uncertainty. Future frameworks should prioritise standardisation of definitions, thresholds, and scoring systems, enabling consistent and transparent decision-making. Expanding beyond SPA qualifying species to multi-species or assemblage-based approaches will deliver broader biodiversity benefits. Climate change adaptation is also essential, as rising sea levels and shifting species distributions will alter habitat requirements.

To address these challenges, the report outlines a decision‑support framework based on three core metrics: connectivity, site abundance, and usage frequency. Sites are classified into three categories (‘core’, ‘primary support’, ‘secondary support’) to guide prioritisation. The framework also clarifies attribution of records to SPA populations and treatment of additional birds, recognises contingency or refuge sites used under specific conditions, and sets out how classification informs boundary inclusion and delineation. Classification informs, but does not alone determine, boundary inclusion; proportionality, practicality, and policy context are applied alongside ecological evidence. Given typical data contexts, assumed connectivity (e.g. known foraging distance and suitable habitat) may often serve as the starting point, with coordinated observations or telemetry used, where proportionate, to increase confidence in connectivity. All assumptions, data limitations, and reasons for inclusion/exclusion should be documented to ensure decisions are transparent and reproducible. The framework also indicates how to identify potential future FLL (e.g. inland refuges under sea‑level rise) to support network resilience, while focusing boundary change on areas with evidence of current or recent functional use. Use of such a structured approach will help ensure that future decisions on SPA boundary extensions are evidence‑based, ecologically robust, and transparent, while remaining adaptable to species ecology, SPA setting, data context, and future environmental change.

Protected Areas Special Protection Area functionally linked land waterfowl Brent Goose Pink-footed Goose Curlew Golden Plover Reports

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