C4. Status of UK priority species

C4b. Distribution


Type: State Indicator



Figure C4bi.  Change in distribution of UK priority species, 1970 to 2012.

Figure C4bi. Change in distribution of UK priority species, 1970 to 2012


  1. Based on 111 species.  The line graph shows the unsmoothed trend (dashed line) and smoothed trend (solid line) with variation around the unsmoothed line (shaded) within which we can be 90% confident that the true value lies (credible interval).
  2. The 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) and Section 42 (Wales), Northern Ireland Priority Species list, Scottish Biodiversity List).

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 declining

2010 indicator stable2007–2012

Decreased (2012)



  • Official lists of priority species have been published for each UK country, and actions to conserve these priority species are included within the respective country strategies.  The species included in the indicator are those on one or more of these priority species lists for which distribution data are available.
  • The indicator shows the average relative change in the distribution of 111 threatened species, as measured by the number of 1km grid squares across the UK in which they were recorded – this is referred to as the ‘occupancy index’.  The indicator will increase when a species becomes more widespread, and will decrease when a species becomes less widespread.
  • Between 1970 and 2012, the occupancy index declined by 35 per cent; 49 per cent of species became less widespread, and 22 per cent became more widespread.
  • The indicator fell by 13 per cent between 2007 and 2012.  Between 2007 and 2012, 55 per cent became less widespread (48 per cent showed a strong decrease), and 42 per cent of species became more widespread (40 per cent showed a strong increase).
  • The measure is a composite indicator of 111 species from the following taxonomic groups for which there are sufficient data to create a time series: bees, wasps, ants, dragonflies, grasshoppers and related insects, ground beetles, moths, bryophytes, and freshwater fish.  Priority species were selected in each country because they are scarce, declining or iconic.  They are not representative of wider species in general.  In addition, the 111 species represent less than 5 per cent of the complete list of priority species, and are not necessarily representative of them.  They do, however, include a range of taxonomic groups, thereby broadening the scope of the priority species indicators, and will respond to the range of environmental pressures that biodiversity policy aims to address, including land-use change, climate change, invasive species, and pollution.

Indicator description

The indicator shows occupancy changes of priority species in the UK: 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) and Section 42 (Wales), Northern Ireland Priority Species list, Scottish Biodiversity List).  The combined list contains 2,890 species in total.  The priority species identified in each of the four UK countries were highlighted as being of conservation concern for a variety of reasons, including rapid decline in some of their populations.  This indicator should be read in conjunction with C4a which provides data on those species for which abundance information is available.

Of these 2,890 species, the 111 for which robust quantitative time-series of the proportion of occupied sites are available are included in the indicator.  These 111 species include bees (40), wasps (15), ants (1), dragonflies (4), bryophytes (7), freshwater fish (3), moths (33), ground beetles (1), grasshoppers and related insects (3), and soldierflies (4).  This selection is taxonomically limited at present.

Occupancy of priority species has declined: between 1970 and 2012 the index fell by 35 per cent.  The index value in 2007 lies within the credible intervals of the index in 2012; therefore the short-term trend is assessed as stable.  Between 2007 and 2012 the indicator declined by 13 per cent.  The credible intervals of the index in 2012 overlapped the index value in 2007, therefore the short-term trend is assessed as 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 background document underpinning this indicator.




Priorities for species and habitat conservation are set at a country level through country biodiversity or environment strategies.  Each country has an identified list of priority species, which are of high conservation concern due, for example, to restricted range or population declines.  The indicator therefore includes a substantial number of species that, by definition, are becoming less widespread.

Measures of distribution are less sensitive to change than measures of abundance (as included in indicator C4a).  Nonetheless, if a species that has been declining starts to recover, its distribution will stabilize, and may start to increase.  If the proportion of species in the indicator that are stable or increasing grows, the indicator will start to decline less steeply.  If the proportion declines, it will fall more steeply.  Success in each country can therefore be judged by reference to trends in indicators C4a and C4b, as well as other information on other priority species for which there are insufficient data for inclusion in the indicator.



The Bayesian occupancy approach enables an estimation of species occurrence even though the data used in this indicator were collected without a standardized survey design (van Strien et al. 2013; Isaac et al. 2014).  For each species, records were extracted at the 1km grid square scale with records on different days being treated separately, and an annual time-series of the proportion of sites occupied was calculated.  Each species-specific time-series was scaled so the first value in 1970 was set to 100.  The annual index was estimated as the arithmetic mean of the scaled species-specific occupancy estimates.  Each species was given equal weighting within the indicator, but because of data gaps not all species contribute to every year of the data.  Uncertainty in the species-specific annual occupancy estimates is represented by the 90 per cent credible intervals.  See the technical background document for further detail on production of the indicator. 

Species were grouped into one of five categories based on both their short-term (over the most recent five years of data) and long-term (all years) mean annual change in occupancy.  The threshold values for each category were based on those of the wild bird indicator.  See the technical background document on the Bayesian indicator development for further detail on the calculation of the species-specific trends.

The trends of the taxonomic groups included within a multi-species indicator are often obscured by its composite nature.  Indicator lines have been generated for a number of sub groups using the same method so that the trends for these groups can be seen more clearly. 

The moths and the “other insects” group (consisting of the grasshoppers and related insects, dragonflies, ground beetles and soldierflies – which were combined due to the small numbers of species included), have undergone the most dramatic decline.  Between 1970 and 2012 the index values fell by 47 per cent for moths, and by 49 per cent for “other insects”.

The bryophytes have also experienced a decline in the proportion of occupied sites since 1970, although over the course of the time series, this is much more variable and the indicator line has a high level of uncertainty.  In 2012, the final index value for bryophytes is 40 per cent of the value in 1970, indicating a decline of 60 per cent.

The bees, wasps and ants group, which contains the greatest number of species, has also experienced an overall decline.  In the final year of the index, this group has an index value of 72 which represents an overall decline of 28 per cent.  However, looking at the indicator as a whole, for the majority of years the index values are just above the baseline of 100, with the decline only being seen in the most recent years.


Figure C4bii.  Change in priority species (probability of occurrence), by taxonomic group, 1970 to 2012.

Figure C4bii. Change in priority species (probability of occurrence), by taxonomic group, 1970 to 2012.


  1. Graphs show the number of species included in brackets, the unsmoothed trend (solid line) and variation around the line (shaded) within which we can be 90% confident that the true value lies.  Freshwater fish are not shown as there are only three species.
  2. 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) and Section 42 (Wales), Northern Ireland Priority Species list, Scottish Biodiversity List).

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

In 2015-16, Defra commissioned a project (reference BE0112), to provide evidence statements to accompany a number of species trend indicators and an overview of the causes of biodiversity change. The output from this project is contained in a methods report, drivers of change report, and summary of evidence.  These are summarised indicator by indicator in a set of Evidence Statements, which aim to ensure that interpretation of trends, casual factors and relationship to policy interventions is rigorous, objective and reflects scientific consensus.

In parallel with the Evidence Statements, Defra also commissioned a Quality Assurance Panel to provide advice on improvements that could be considered to the species based indicators in the UK and England biodiversity indicator sets. The report of the review has led to an action plan of changes to be made as resources allow.


Further development planned

Data are available for a number of additional taxonomic groups which are represented on the combined Four Countries List.  Due to time constraints these could not be added to this year’s indicator, however there is the potential to add these groups in future years. 

Whilst the Bayesian occupancy model is the preferred tool for future indicators, further research is required to assess whether the short-term trends should be evaluated over five years, or over a longer period.  While they may show evidence of change in relation to conservation policy, disentangling this from short-term effects of weather is a challenge.  Currently, a smoothed line has been added to the headline indicator to make the overall trend clear to observe.  An assessment based on the smoothed indicator should be investigated in future iterations of the indicator.  Using a smoothed trend should reduce the influence of short-term weather variation on the indicator.

Further work to investigate how to model the trends for species that failed the data requirements of the Bayesian occupancy model may help to evaluate changes in more priority species.  Initial work using the Frescalo technique (Hill 2012) seems promising. 

As the sample size increases it may become possible to investigate other ways to break down the indicator; possibilities include, by country, upland/lowland, ecosystems/habitats, traits/life history strategies and or by trophic level.


Goals and targets

Aichi Targets for which this is a primary indicator

Strategic Goal C. To improve the status of biodiversity by safeguarding ecosystems, species and genetic diversity.

Aichi icon 12Target 12: By 2020, the extinction of known threatened species has been prevented and their conservation status, particularly of those most in decline, has been improved and sustained.


Aichi Targets for which this is a relevant indicator

Strategic Goal B. Reduce the direct pressures on biodiversity and promote sustainable use.

Aichi icon 5Target 5: By 2020, the rate of loss of all natural habitats, including forests, is at least halved and where feasible brought close to zero, and degradation and fragmentation is significantly reduced.


Strategic Goal C. To improve the status of biodiversity by safeguarding ecosystems, species and genetic diversity.

Aichi icon 11Target 11: By 2020, at least 17 per cent of terrestrial and inland water, and 10 per cent of coastal and marine areas, especially areas of particular importance for biodiversity and ecosystem services, are conserved through effectively and equitably managed, ecologically representative and well connected systems of protected areas and other effective area-based conservation measures, and integrated into the wider landscape and seascapes.


Web links for further information




British Arachnological Society – Spider and Harvestman Recording Scheme

Home page


Bees, Wasps & Ants Recording Society

Identification guides to download


British Bryological Society

Home page


British Dragonfly Society

Recording Dragonflies and Damselflies in the British Isles


British Myriapod and Isopod Group

Centipede and Millipede recording schemes


Butterfly Conservation

Butterflies and moths


Centre for Ecology & Hydrology – Biological Records Centre

Recording Schemes



Diperists Forum


Cranefly and Empididae & Dolichopodidae Recording Schemes


Ground Beetle Recording Scheme

Home page



Hoverfly Recording Scheme

Home page


National Moth Recording Scheme

Home page


Orthoptera Recording Scheme

Home page


Riverfly Recording Schemes:


Home page



Soldierflies and Allies Recording Scheme

Home page


UK Biodiversity Partnership

UK Biodiversity Action Plans


The Scottish Government

Scottish Biodiversity List



Wales Biodiversity Partnership

S42 List of priority species in Wales



Natural England

S41 List of priority species in England



Northern Ireland Environment Agency

Northern Ireland Priority Species List


Defra Evidence Statements project: Method report http://sciencesearch.defra.gov.uk/Document.aspx?Document=13933_BE0112FinalReport.pdf
Defra Evidence Statements project: Drivers of Change http://sciencesearch.defra.gov.uk/Document.aspx?Document=13945_Annex2_DriversOfChange.pdf
Defra Evidence Statements project: Summary of Evidence http://sciencesearch.defra.gov.uk/Document.aspx?Document=13947_Annex3_SummaryOfEvidence.pdf
Defra Quality Assurance Science Panel report View QASP report



Hill, M.0. (2012) Local frequency as a key to interpreting species occurrence data when recording effort is not known. Methods in Ecology and Evolution, 3(1), 195–205.

Isaac, N.J.B., August, T.A., Harrower, C. & Roy, D.B. (2013) Trends in the Distribution of UK native species 1970-2010. Preliminary report to JNCC. JNCC Report No 488. http://jncc.defra.gov.uk/pdf/488_Web.pdf (PDF, 205kb).

Isaac, N.J.B., van Strien, A.J., August, T.A., de Zeeuw, M.P. & Roy, D.B. (2014a) Statistics for citizen science: extracting signals of change from noisy ecological data. Methods in Ecology and Evolution. doi:10.1111/2041-210X.12254

Isaac, N.J.B., van Strien, A.J., August, T.A., de Zeeuw, M.P. & Roy, D.B. (2014b) Extracting robust trends in species’ distributions from unstructured opportunistic data: a comparison of methods. BioRXiv. doi:10.1101/006999.

Van Strien, A.J., van Swaay, C.A.M. & Termaat, T. (2013) Opportunistic citizen science data of animal species produce reliable estimates of distribution trends if analysed with occupancy models. Journal of Applied Ecology, 50(6), 1450–1458. doi:10.1111/1365-2664.12158


Download Datasheet 

Download Technical background document

Download Technical background document on Bayesian Occupancy Models

Download Evidence statement


Last updated: November 2016

Latest data: 2012