The existing guidance specification for the selection of SSSIs for birds includes the quality of the breeding bird assemblages of different habitats occurring in Britain. This guidance was based, to some extent, on Bird Habitats in Britain and, at that time, the BTO Register of Ornithological Sites. Bird populations, distribution and habitat preferences have changed greatly since 1989 and the current breeding bird assemblage guidance is no longer entirely suitable for SSSI selection. 

All elements of the guidance required reviewing and updating, including habitat definitions, component species and resulting ‘threshold scores’ for each habitat. The process for calculating ‘threshold scores’ for assessing the quality of the breeding bird assemblage within any particular habitat type is described in section 4. 

In this document we update the breeding bird assemblage guidelines using the latest available information for all relevant bird species. The details include the most recent estimates and information for Great Britain on population size, distribution and habitat requirements. All data sources and methods used to update the guidelines are described. 

Tables are produced for each habitat showing the component species, amended species rank scores based on their current population size and the suggested overall threshold scores required for individual site designation. Entirely new guidelines are created for breeding bird assemblages of lowland farmland (arable, grassland and mixed) and upland in-bye (e.g. rough pastures, pastures and meadows) and Welsh ffridd habitats which tend to be mosaics of bracken, grassland and scrub.