C4. Status of UK priority species

C4b. Distribution


Type: State Indicator


Indicator Description

The indicator measures change in the number of 1km grid squares across the UK in which priority species were recorded in any given year – this is referred to as the ‘occupancy index’ and is effectively equivalent to changes in distribution of the species.  The indicator will increase when a species becomes more widespread, and will decrease when a species becomes less widespread.  This indicator should be read in conjunction with C4a which provides data on those species for which abundance information is available.



Between 1970 and 2016, the index was relatively stable; with an even balance of species increasing and decreasing.     

The indicator fell by 10% between 1970 and 1990, this was followed by a steady increase until the early 2000s when the composite trend remained stable up to 2016.  The index value in 2016 was 5% higher than the value in 1970, however this increase is not statistically significant.

Priority species are defined as those on one or more of the biodiversity lists of each UK country (Natural Environmental and Rural Communities Act 2006 - Section 41 (England); Environment (Wales) Act 2016 section 7, Northern Ireland Priority Species List, Scottish Biodiversity List).  The combined list contains 2,890 species in total.  The priority species were highlighted as being of conservation concern for a variety of reasons, including rapid decline in some of their populations.


Figure C4bi.  Change in distribution of UK priority species, 1970 to 2015.

Figure C4bi. Change in distribution of UK priority species, 1970 to 2015


  1. Based on 714 species.  Graph shows the unsmoothed composite indicator trend (dotted line) with variation around the line (shaded) within which we can be 90% confident that the true value lies (credible interval).
  2. Bar chart shows the percentage of species within the indicator that have increased, decreased or shown no change in distribution (measured as the proportion of occupied sites), based on set thresholds of change. 
  3. All species in the indicator are present on one or more of the country priority species lists (Natural Environmental and Rural Communities Act 2006 – Section 41 (England), Environment (Wales) Act 2016 section 7, Northern Ireland Priority Species list, Scottish Biodiversity List).
  4. As a result of methodological improvements in the occupancy model analysis, a greater number of taxonomic groups and species have been able to be included compared to the 2015 C4b indicator.  Therefore, this chart is not directly comparable to previous versions of this indicator.

Source: Biological records data collated by a range of national schemes and local data centres.


Assessment of change in distribution of priority species in the UK


Long term

Short term

Latest year

Priority species – Distribution

2010 indicator stable1970–2016

2010 indicator stable2011–2016

Increased (2016)


Of the 2,890 species on the combined priority species list, the 714 for which robust quantitative time-series of the proportion of occupied sites are available are included in the indicator. Relative change in distribution is measured by the number of 1km grid squares across the UK in which they were recorded – this is referred to as the ‘occupancy index’.

Occupancy of priority species was assessed as stable between 1970 and 2016.  The index in 2016 was 5% higher than in 1970, but taking into account the 90% credible interval this is not considered a significant change.  Similarly between 2011 and 2016 the indicator was stable. Uncertainty in the species-specific annual occupancy estimates are incorporated into the overall indicator; details of how this was done are included in the technical report underpinning this indicator.


Download Fiche

Download Datasheet 

Download Technical background document

Download Technical background document on Bayesian Occupancy Models

Download Evidence statement


Last updated: August 2017

Latest data: 2016