Information - This Indicator is an official statistic in development and has been published in order to facilitate user involvement in its development – information on how the data have been obtained and how the indicator has been prepared is available via the link(s) in the 'Readiness and links to data' section. We would welcome any feedback, particularly on the usefulness and value of this statistic, via 25YEPindicators@defra.gov.uk.
D6: Relative abundance and distribution of priority species in England
Short Description
Priority Species are those identified as the most threatened or declining species in the UK. They were identified to support UK conservation planning and are published and maintained by the Joint Nature Conservation Committee. Priority species are used as the reference source to produce statutory species lists of principal conservation importance. Such lists are published by the Secretary of State under Section 41 of the Natural Environment and Rural Communities Act 2006. There are 940 priority species recognised in England.
This indicator has two components: (a) changes in the relative abundance of those priority species for which suitable abundance data are available; and (b) changes in the distribution of those priority species for which suitable distribution data are available. The relative abundance of a species will increase when the population of the species grows, and it will decrease when the population of the species declines. The distribution index, also referred to as the occupancy index, measures the number of 1 kilometre grid squares across the country in which species are recorded each year. It will increase when a species becomes more widespread and decrease when a species becomes less widespread.
Readiness and links to data
An interim indicator is presented here showing trends for the relative abundance and distribution of priority species at an England-level. A newly developed relative abundance measure was incorporated into this indicator in 2024. Further details about this abundance measure, including taxonomic breakdowns, a technical background section that describes the data sources and methods in greater detail, and a spreadsheet that contains a list of species within the index together with a more granular breakdown of the data are available in the annual Indicators of species abundance in England statistics release. The data are published as an official statistic in development to gather feedback and facilitate user involvement in the development of the indicator.
Further details about the distribution measure are published annually as England Biodiversity Indicator – Status of priority species: distribution. This includes a technical background document that describes the data sources and methods in detail, a list of species within the index, and a spreadsheet that contains a more granular breakdown of the data.
Methods are being developed to refine the future reporting of this indicator and to expand the taxonomic coverage.
Notes on indicator
The taxonomic coverage of this indicator is limited at present. The relative abundance measure includes priority birds, butterflies, moths, some mammals (one hare, one dormouse, one water vole and five bats), some fish, two freshwater invertebrates, one bumblebee and one vascular plant. It does not currently include any fungi, amphibians, or reptiles. The distribution measure includes priority species of bryophytes, lichens, insects and other invertebrates but does not currently include amphibians, reptiles, birds, fish or mammals. Species will be added to this indicator if they are included on the priority species list and suitable data become available, or if they become recognised as priority species and suitable data is available that meets the criteria set out in the Technical annex of Indicators of species abundance in England.
Two possible versions of the relative abundance measure are currently presented here, 'option 1' with a greater degree of smoothing applied (using a 10-year timescale) and 'option 2' with a lesser degree of smoothing (using a 3-year timescale). Smoothing is applied to the species abundance indicator to identify long-term trends in otherwise noisy data. A greater degree of smoothing may provide a clearer view of the underlying long-term trend, while a lesser degree of smoothing preserves the shorter-term patterns in the data. The results given in the commentary are based on the values of both trends and are intended to communicate the extent to which reliance of these trends are dependent on methodological decisions. Further details on this methodology are available in the Indicators of species abundance in England statistical release.
While the data currently available on the distribution of priority species in England presented in indicator D6b mostly predate the 25 Year Environment Plan, they provide the most recently available assessment of this measure. They also enable a better understanding of a baseline from which to measure progress towards the goals of the 25 Year Environment Plan when the indicator is next updated.
Indicator components
Figure D6ai: Relative abundance of priority species in England, 1970 to 2023
Table D6ai: Relative abundance of priority species in England, 1970 to 2023
| Year | Smoothed index (option 1) | 95% credible interval lower bound (option 1) | 95% credible interval upper bound (option 1) | Smoothed index (option 2) | 95% credible interval lower bound (option 2) | 95% credible interval upper bound (option 2) |
|---|---|---|---|---|---|---|
| 1970 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 |
| 1971 | 92.20 | 90.30 | 94.30 | 89.70 | 87.40 | 92.00 |
| 1972 | 86.10 | 82.80 | 89.50 | 83.00 | 79.60 | 86.50 |
| 1973 | 81.30 | 77.10 | 85.70 | 78.70 | 74.70 | 83.20 |
| 1974 | 77.50 | 72.70 | 82.30 | 76.30 | 71.90 | 81.30 |
| 1975 | 74.40 | 69.20 | 79.80 | 75.20 | 70.20 | 80.80 |
| 1976 | 71.90 | 66.50 | 77.50 | 74.60 | 69.00 | 80.50 |
| 1977 | 69.90 | 64.30 | 75.70 | 73.40 | 67.30 | 79.90 |
| 1978 | 68.10 | 62.50 | 74.10 | 71.00 | 64.70 | 77.60 |
| 1979 | 66.60 | 60.70 | 72.80 | 67.80 | 61.50 | 74.60 |
| 1980 | 65.10 | 59.00 | 71.70 | 64.80 | 58.60 | 71.80 |
| 1981 | 63.70 | 57.40 | 70.40 | 62.90 | 56.60 | 70.00 |
| 1982 | 62.20 | 55.70 | 69.30 | 61.90 | 55.60 | 69.20 |
| 1983 | 60.60 | 54.20 | 67.80 | 60.90 | 54.50 | 68.50 |
| 1984 | 58.90 | 52.40 | 66.10 | 59.40 | 52.90 | 66.80 |
| 1985 | 57.10 | 50.60 | 64.30 | 57.20 | 50.70 | 64.50 |
| 1986 | 55.00 | 48.60 | 62.30 | 54.80 | 48.30 | 61.90 |
| 1987 | 52.90 | 46.60 | 59.90 | 52.20 | 46.00 | 59.30 |
| 1988 | 50.60 | 44.40 | 57.50 | 49.90 | 43.80 | 56.90 |
| 1989 | 48.30 | 42.30 | 55.10 | 47.80 | 41.70 | 54.80 |
| 1990 | 45.90 | 40.10 | 52.60 | 46.00 | 39.90 | 53.00 |
| 1991 | 43.50 | 38.00 | 50.10 | 44.20 | 38.20 | 51.00 |
| 1992 | 41.20 | 35.90 | 47.60 | 42.30 | 36.50 | 49.10 |
| 1993 | 38.90 | 33.80 | 45.10 | 40.20 | 34.50 | 47.00 |
| 1994 | 36.80 | 31.80 | 42.70 | 38.00 | 32.50 | 44.60 |
| 1995 | 34.80 | 30.00 | 40.50 | 35.60 | 30.40 | 41.90 |
| 1996 | 32.90 | 28.30 | 38.40 | 33.00 | 28.00 | 38.90 |
| 1997 | 31.20 | 26.80 | 36.50 | 30.40 | 25.70 | 35.90 |
| 1998 | 29.70 | 25.50 | 34.80 | 28.00 | 23.70 | 33.10 |
| 1999 | 28.50 | 24.40 | 33.50 | 26.20 | 22.10 | 31.00 |
| 2000 | 27.40 | 23.50 | 32.30 | 25.40 | 21.40 | 30.20 |
| 2001 | 26.60 | 22.70 | 31.30 | 25.50 | 21.50 | 30.40 |
| 2002 | 26.00 | 22.10 | 30.70 | 26.20 | 22.00 | 31.20 |
| 2003 | 25.50 | 21.70 | 30.30 | 26.60 | 22.40 | 32.00 |
| 2004 | 25.20 | 21.50 | 29.90 | 26.50 | 22.20 | 31.80 |
| 2005 | 25.10 | 21.30 | 29.70 | 26.00 | 21.80 | 31.10 |
| 2006 | 25.00 | 21.30 | 29.80 | 25.20 | 21.10 | 30.20 |
| 2007 | 25.10 | 21.20 | 29.80 | 24.70 | 20.60 | 29.60 |
| 2008 | 25.10 | 21.20 | 29.90 | 24.70 | 20.60 | 29.60 |
| 2009 | 25.20 | 21.20 | 30.20 | 25.30 | 21.10 | 30.40 |
| 2010 | 25.30 | 21.30 | 30.30 | 26.10 | 21.80 | 31.50 |
| 2011 | 25.30 | 21.20 | 30.30 | 26.50 | 22.10 | 31.90 |
| 2012 | 25.30 | 21.20 | 30.30 | 26.10 | 21.70 | 31.50 |
| 2013 | 25.30 | 21.10 | 30.30 | 25.20 | 21.00 | 30.50 |
| 2014 | 25.20 | 20.90 | 30.20 | 24.20 | 20.20 | 29.40 |
| 2015 | 25.00 | 20.80 | 30.00 | 23.50 | 19.50 | 28.60 |
| 2016 | 24.80 | 20.60 | 29.90 | 23.30 | 19.30 | 28.30 |
| 2017 | 24.60 | 20.40 | 29.60 | 23.30 | 19.30 | 28.40 |
| 2018 | 24.30 | 20.10 | 29.40 | 23.60 | 19.50 | 28.90 |
| 2019 | 24.00 | 19.80 | 29.20 | 24.00 | 19.80 | 29.40 |
| 2020 | 23.80 | 19.50 | 28.90 | 24.10 | 19.90 | 29.70 |
| 2021 | 23.50 | 19.30 | 28.60 | 24.00 | 19.80 | 29.60 |
| 2022 | 23.20 | 19.00 | 28.20 | 23.50 | 19.30 | 29.10 |
| 2023 | 22.90 | 18.70 | 27.80 | 22.70 | 18.50 | 28.00 |
Trend description for D6ai
By 2023, the index of change in the relative abundance of priority species in England had declined to around 23% of its baseline value in 1970, with the majority of these changes taking place in the last three decades of the 20th century. More recently, between 2018 and 2023, the relative abundance index showed no meaningful change over the latest five years for which data are currently available.
Assessment of change
The composite relative abundance of priority species measure is also reported in Indicators of species abundance in England. This statistical release presents a short-, medium- and long-term assessment for the same time periods used in this Outcome Indicator Framework assessment. These assessment results were reused here as the method in the source publication is tailored to the specific composite abundance index and it factors-in information on confidence. The assessment found little or no change in the relative abundance of priority species in England over the short- and medium-term periods and a decline (deterioration) over the long-term.
Details on the assessment methodology used for this indicator can be found in the ‘assessment of change’ section of the Indicators of species abundance in England statistical release. Further information on the standard assessment used in the Outcome Indicator Framework, along with details on the methodology, is provided in the Assessment background page. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results pages.
Table D6ai: Assessment of change
| Component | Subcomponent | Period | Date range | Percentage change | Smoothing function | Assessment of change |
|---|---|---|---|---|---|---|
| D6ai | Smoothed index (options 1 and 2) | Short term | 2018 to 2023 | -5.8 to -3.8 | Smoothed data | Little or no change |
| D6ai | Smoothed index (options 1 and 2) | Medium term | 2013 to 2023 | -9.5 to -9.9 | Smoothed data | Little or no change |
| D6ai | Smoothed index (options 1 and 2) | Long term | 1970 to 2023 | -77.1 to -77.30 | Smoothed data | Deterioration |
Note that smoothed data presented in the indicator charts were used for percentage change calculations. The smoothing method is specific to this indicator and differs from the default Loess smoothing approach adopted for most indicators for the Outcome Indicator Framework assessment. Percentage change refers to the difference seen between the first and last years in the specified date range.
Figure D6aii: Long-term and short-term changes in the relative abundance of individual priority species in England, 1970 to 2023
Table D6aii: Long-term and short-term changes in the relative abundance of individual priority species in England, 1970 to 2023
| Period | Strong decrease | Weak decrease | Little or no change | Weak increase | Strong increase |
|---|---|---|---|---|---|
| Long term (1970–2023) | 45.30 | 20.50 | 17.40 | 5.60 | 11.20 |
| Short term (2018–2023) | 34.00 | 11.30 | 13.80 | 8.80 | 32.10 |
Trend description for D6aii
The long-term decline in the overall abundance of priority species in England shown in D6ai reflects the trends of the individual species within the index, 66% of which showed a strong or weak decrease and 17% of which showed a strong or weak increase in abundance since 1970. Over the short-term period (between 2018 and 2023), 45% showed a strong or weak decrease and 41% of species showed a strong or weak increase in abundance over the latest five years for which data are currently available.
Assessment of change
No assessment of change was undertaken for this indicator as it is based on the same underlying data that are already assessed in D6ai.
Figure D6bi: Distribution of priority species in England, 1970 to 2016
Table D6bi: Distribution of priority species in England, 1970 to 2016
| Year | Smoothed index | 95% credible interval lower bound | 95% credible interval upper bound |
|---|---|---|---|
| 1970 | 100.00 | 100.00 | 100.00 |
| 1971 | 100.37 | 98.65 | 102.18 |
| 1972 | 100.14 | 97.80 | 102.56 |
| 1973 | 99.71 | 97.02 | 102.47 |
| 1974 | 99.33 | 96.56 | 102.20 |
| 1975 | 99.28 | 96.37 | 102.16 |
| 1976 | 98.93 | 96.07 | 101.77 |
| 1977 | 97.46 | 94.60 | 100.27 |
| 1978 | 96.36 | 93.50 | 99.20 |
| 1979 | 95.56 | 92.60 | 98.47 |
| 1980 | 94.62 | 91.72 | 97.52 |
| 1981 | 93.78 | 90.95 | 96.74 |
| 1982 | 94.06 | 91.20 | 97.06 |
| 1983 | 94.34 | 91.42 | 97.32 |
| 1984 | 93.96 | 91.12 | 96.93 |
| 1985 | 92.79 | 89.99 | 95.71 |
| 1986 | 91.89 | 89.16 | 94.70 |
| 1987 | 91.61 | 88.92 | 94.37 |
| 1988 | 91.32 | 88.59 | 94.06 |
| 1989 | 91.79 | 89.00 | 94.58 |
| 1990 | 92.35 | 89.60 | 95.21 |
| 1991 | 92.32 | 89.65 | 95.11 |
| 1992 | 91.92 | 89.24 | 94.62 |
| 1993 | 91.56 | 88.97 | 94.26 |
| 1994 | 92.10 | 89.43 | 94.73 |
| 1995 | 93.39 | 90.72 | 96.14 |
| 1996 | 94.13 | 91.45 | 96.86 |
| 1997 | 94.33 | 91.79 | 96.98 |
| 1998 | 93.25 | 90.73 | 95.94 |
| 1999 | 93.14 | 90.65 | 95.77 |
| 2000 | 93.61 | 90.98 | 96.23 |
| 2001 | 94.55 | 91.97 | 97.24 |
| 2002 | 95.21 | 92.67 | 97.90 |
| 2003 | 95.95 | 93.33 | 98.64 |
| 2004 | 95.49 | 92.91 | 98.14 |
| 2005 | 95.31 | 92.80 | 97.97 |
| 2006 | 95.12 | 92.51 | 97.81 |
| 2007 | 91.74 | 89.12 | 94.42 |
| 2008 | 90.79 | 88.20 | 93.47 |
| 2009 | 91.90 | 89.32 | 94.67 |
| 2010 | 92.29 | 89.50 | 95.20 |
| 2011 | 92.26 | 89.49 | 95.13 |
| 2012 | 89.06 | 86.24 | 92.12 |
| 2013 | 89.86 | 86.96 | 93.05 |
| 2014 | 88.24 | 85.28 | 91.52 |
| 2015 | 86.15 | 82.71 | 89.65 |
| 2016 | 83.68 | 79.39 | 87.94 |
Trend description for D6bi
By 2016, the index of distribution of priority species in England had declined to 83.7, a decrease of around 16% from its 1970 value. More recently, between 2011 and 2016, the distribution index declined from 92.3 to 83.7 (by around 9% of the 2011 value), again a meaningful decrease over the latest five years for which data are currently available.
Assessment of change
An indicator for the distribution of priority species in England is also reported in the England Biodiversity Indicators, which presents a short- and long-term assessment for the same time periods used in this Outcome Indicator Framework assessment. The assessment methodology and results from the England Biodiversity Indicators are reused here as they are more tailored to the specific dataset and factor-in information on confidence. The same methodology is also used to calculate a medium-term assessment. The assessment found a decline (deterioration) in the distribution of priority species in England over the short- and long-term time periods.
Change since 2018 has not been assessed for this indicator as sufficient data are not yet available.
Details on the England Biodiversity Indicators assessment methodology for this indicator can be found in section 2 of the latest England Biodiversity Indicators report. Further information on the standard assessment used in the Outcome Indicator Framework, along with details on the methodology, is provided in the Assessment background page. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results pages.
Table D6bi: Assessment of change
| Component | Subcomponent | Period | Date range | Percentage change | Smoothing function | Assessment of change |
|---|---|---|---|---|---|---|
| D6bi | Smoothed index | Short term | 2011 to 2016 | -9.30 | Smoothed data | Deterioration |
| D6bi | Smoothed index | Medium term | 2006 to 2016 | -12.03 | Smoothed data | Deterioration |
| D6bi | Smoothed index | Long term | 1970 to 2016 | -16.32 | Smoothed data | Deterioration |
Note that smoothed data presented in the indicator charts were used for percentage change calculations. The smoothing method is specific to this indicator and differs from the default Loess smoothing approach adopted for most indicators for the Outcome Indicator Framework assessment. Percentage change refers to the difference seen between the first and last years in the specified date range.
Figure D6bii: Long-term and short-term changes in the distribution of individual priority species in England, 1970 to 2016
Table D6bii: Long-term and short-term changes in the distribution of individual priority species in England, 1970 to 2016
| Time period | Strong decrease | Weak decrease | Little or no change | Weak increase | Strong increase |
|---|---|---|---|---|---|
| Long term (1970-2016) | 17.13 | 20.99 | 37.57 | 9.39 | 14.92 |
| Short term (2011-2016) | 31.49 | 27.07 | 28.18 | 8.29 | 4.97 |
Trend description for D6bii
The long-term decline in the overall distribution of priority species in England shown in D6bi masks the trends of the individual species within the index, with 38% showing a decrease in distribution and 24% of species showing an increase in distribution since 1970. Over the short-term period (2011 to 2016), 59% of priority species showed a decrease in distribution and 13% of species showed an increase in distribution over the latest five years for which data are currently available.
Assessment of change
No assessment of change was undertaken for this indicator as it is based on the same underlying data that are already assessed in D6bi.