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 2 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
This indicator is not available for reporting in 2024 in a finalised form. Trends for the relative abundance and distribution of priority species at an England-level were presented here for the first time in 2021 as an interim indicator; however, a new relative abundance measure has recently been developed, and it is presented here for the first time in 2024 as a revised interim indicator.
Further details about the new 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 being 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 including a technical background document that describes the data sources and methods in detail and include a list of species within the index, and a spreadsheet that contains a more granular breakdown of the data are published annually as England Biodiversity Indicator 4b – Status of priority species: distribution.
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 and some mammals (one hare, one dormouse and five bats), but does not currently include plants, fungi, amphibians, reptiles, fish or invertebrates other than butterflies and moths; the distribution measure includes priority species of bryophytes, lichens, insects and other invertebrates but does not currently include amphibians, reptiles, birds, fish or mammals.
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 currently available data 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 2022
Table D6ai: Relative abundance of priority species in England, 1970 to 2022
| Year | 95% credible interval lower bound (option 1) | 95% credible interval lower bound (option 2) | 95% credible interval upper bound (option 1) | 95% credible interval upper bound (option 2) | Smoothed index (option 1) | Smoothed index (option 2) |
|---|---|---|---|---|---|---|
| 1970 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 |
| 1971 | 90.30 | 87.10 | 94.30 | 91.80 | 92.30 | 89.40 |
| 1972 | 82.90 | 79.10 | 89.60 | 86.10 | 86.20 | 82.50 |
| 1973 | 77.20 | 74.20 | 85.70 | 82.60 | 81.30 | 78.30 |
| 1974 | 72.70 | 71.50 | 82.40 | 81.10 | 77.40 | 76.10 |
| 1975 | 69.30 | 70.20 | 79.60 | 80.80 | 74.30 | 75.20 |
| 1976 | 66.50 | 69.50 | 77.50 | 81.00 | 71.80 | 74.90 |
| 1977 | 64.20 | 68.00 | 75.60 | 80.40 | 69.70 | 73.80 |
| 1978 | 62.20 | 65.50 | 74.20 | 78.20 | 68.00 | 71.30 |
| 1979 | 60.50 | 62.00 | 72.70 | 74.70 | 66.40 | 67.90 |
| 1980 | 58.90 | 58.80 | 71.50 | 71.70 | 64.90 | 64.80 |
| 1981 | 57.40 | 56.90 | 70.20 | 69.80 | 63.50 | 62.80 |
| 1982 | 55.90 | 55.50 | 68.70 | 68.80 | 62.00 | 61.70 |
| 1983 | 54.10 | 54.50 | 67.30 | 67.90 | 60.40 | 60.70 |
| 1984 | 52.40 | 53.00 | 65.80 | 66.40 | 58.70 | 59.20 |
| 1985 | 50.60 | 50.70 | 64.00 | 64.40 | 56.90 | 57.00 |
| 1986 | 48.60 | 48.20 | 61.90 | 61.60 | 54.90 | 54.40 |
| 1987 | 46.60 | 45.50 | 59.70 | 58.70 | 52.70 | 51.60 |
| 1988 | 44.40 | 43.20 | 57.20 | 55.90 | 50.50 | 49.10 |
| 1989 | 42.20 | 41.30 | 54.80 | 53.70 | 48.10 | 47.10 |
| 1990 | 40.00 | 39.80 | 52.20 | 52.10 | 45.70 | 45.40 |
| 1991 | 37.80 | 38.20 | 49.60 | 50.50 | 43.30 | 43.80 |
| 1992 | 35.50 | 36.50 | 47.10 | 48.30 | 40.90 | 41.80 |
| 1993 | 33.60 | 34.60 | 44.60 | 46.00 | 38.60 | 39.80 |
| 1994 | 31.50 | 32.80 | 42.20 | 43.90 | 36.40 | 37.70 |
| 1995 | 29.60 | 30.80 | 39.90 | 41.40 | 34.40 | 35.60 |
| 1996 | 27.90 | 28.70 | 37.90 | 38.80 | 32.50 | 33.20 |
| 1997 | 26.40 | 26.30 | 36.00 | 35.60 | 30.80 | 30.50 |
| 1998 | 25.10 | 24.00 | 34.40 | 32.60 | 29.30 | 27.80 |
| 1999 | 23.90 | 22.30 | 33.00 | 30.40 | 28.00 | 25.80 |
| 2000 | 22.90 | 21.50 | 31.80 | 29.60 | 27.00 | 25.00 |
| 2001 | 22.20 | 21.50 | 30.90 | 29.70 | 26.10 | 25.10 |
| 2002 | 21.60 | 21.90 | 30.20 | 30.30 | 25.40 | 25.60 |
| 2003 | 21.10 | 22.20 | 29.70 | 30.80 | 24.90 | 26.00 |
| 2004 | 20.80 | 22.20 | 29.20 | 30.90 | 24.60 | 26.00 |
| 2005 | 20.50 | 21.60 | 29.10 | 30.20 | 24.30 | 25.30 |
| 2006 | 20.30 | 20.70 | 28.90 | 29.00 | 24.10 | 24.30 |
| 2007 | 20.00 | 20.00 | 28.70 | 28.00 | 24.00 | 23.50 |
| 2008 | 19.90 | 19.90 | 28.50 | 27.80 | 23.80 | 23.40 |
| 2009 | 19.60 | 20.20 | 28.30 | 28.30 | 23.60 | 23.80 |
| 2010 | 19.40 | 20.40 | 28.00 | 28.80 | 23.30 | 24.20 |
| 2011 | 19.10 | 20.20 | 27.70 | 28.70 | 23.10 | 24.00 |
| 2012 | 18.80 | 19.30 | 27.30 | 27.60 | 22.70 | 23.10 |
| 2013 | 18.40 | 18.40 | 26.90 | 26.20 | 22.30 | 21.90 |
| 2014 | 18.10 | 17.60 | 26.50 | 25.00 | 22.00 | 20.90 |
| 2015 | 17.80 | 16.90 | 26.10 | 24.30 | 21.60 | 20.20 |
| 2016 | 17.50 | 16.60 | 25.70 | 24.00 | 21.20 | 19.90 |
| 2017 | 17.20 | 16.80 | 25.40 | 24.20 | 20.90 | 20.10 |
| 2018 | 17.00 | 17.10 | 25.30 | 24.80 | 20.70 | 20.50 |
| 2019 | 16.90 | 17.30 | 25.20 | 25.30 | 20.60 | 20.90 |
| 2020 | 16.90 | 17.50 | 25.20 | 25.70 | 20.60 | 21.10 |
| 2021 | 17.00 | 17.60 | 25.50 | 25.80 | 20.80 | 21.10 |
| 2022 | 17.30 | 17.20 | 26.10 | 25.50 | 21.10 | 20.90 |
Trend description for D6ai
By 2022, the index of change in the relative abundance of priority species in England had declined to around 21% of its baseline value in 1970, with the majority of these changes taking place in the last 3 decades of the 20th century. More recently, between 2017 and 2022, the relative abundance index showed no significant change over the latest 5 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.
Change since 2018 has also been assessed using the same methodology as the source publication. There has been little or no change in the index for relative abundance of priority species in England since 2018. However, this result is based on only 5 data points so should be considered as indicative and not evidence of a clear trend.
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 | 2017 to 2022 | 0.96 to 3.98 | Smoothed data | Little or no change |
| D6ai | Smoothed index (options 1 and 2) | Medium term | 2012 to 2022 | -7.05 to -9.52 | Smoothed data | Little or no change |
| D6ai | Smoothed index (options 1 and 2) | Long term | 1970 to 2022 | -78.90 to -79.10 | 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 2022
Table D6aii: Long-term and short-term changes in the relative abundance of individual priority species in England, 1970 to 2022
| Period | Little or no change | Strong decrease | Strong increase | Weak decrease | Weak increase |
|---|---|---|---|---|---|
| Long term (1970–2022) | 18.79 | 42.95 | 9.40 | 25.50 | 3.36 |
| Short term (2017–2022) | 10.42 | 29.17 | 43.75 | 9.03 | 7.64 |
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, 68% of which showed a strong or weak decrease and 13% of which showed a strong or weak increase in abundance since 1970. Over the short-term period (between 2017 and 2022), the situation is more favourable with 51% of species showing a strong or weak increase and 38% showing a strong or weak decrease in abundance over the latest 5 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 | 95% credible interval lower bound | 95% credible interval upper bound | Smoothed index |
|---|---|---|---|
| 1970 | 100.00 | 100.00 | 100.00 |
| 1971 | 98.65 | 102.18 | 100.37 |
| 1972 | 97.80 | 102.56 | 100.14 |
| 1973 | 97.02 | 102.47 | 99.71 |
| 1974 | 96.56 | 102.20 | 99.33 |
| 1975 | 96.37 | 102.16 | 99.28 |
| 1976 | 96.07 | 101.77 | 98.93 |
| 1977 | 94.60 | 100.27 | 97.46 |
| 1978 | 93.50 | 99.20 | 96.36 |
| 1979 | 92.60 | 98.47 | 95.56 |
| 1980 | 91.72 | 97.52 | 94.62 |
| 1981 | 90.95 | 96.74 | 93.78 |
| 1982 | 91.20 | 97.06 | 94.06 |
| 1983 | 91.42 | 97.32 | 94.34 |
| 1984 | 91.12 | 96.93 | 93.96 |
| 1985 | 89.99 | 95.71 | 92.79 |
| 1986 | 89.16 | 94.70 | 91.89 |
| 1987 | 88.92 | 94.37 | 91.61 |
| 1988 | 88.59 | 94.06 | 91.32 |
| 1989 | 89.00 | 94.58 | 91.79 |
| 1990 | 89.60 | 95.21 | 92.35 |
| 1991 | 89.65 | 95.11 | 92.32 |
| 1992 | 89.24 | 94.62 | 91.92 |
| 1993 | 88.97 | 94.26 | 91.56 |
| 1994 | 89.43 | 94.73 | 92.10 |
| 1995 | 90.72 | 96.14 | 93.39 |
| 1996 | 91.45 | 96.86 | 94.13 |
| 1997 | 91.79 | 96.98 | 94.33 |
| 1998 | 90.73 | 95.94 | 93.25 |
| 1999 | 90.65 | 95.77 | 93.14 |
| 2000 | 90.98 | 96.23 | 93.61 |
| 2001 | 91.97 | 97.24 | 94.55 |
| 2002 | 92.67 | 97.90 | 95.21 |
| 2003 | 93.33 | 98.64 | 95.95 |
| 2004 | 92.91 | 98.14 | 95.49 |
| 2005 | 92.80 | 97.97 | 95.31 |
| 2006 | 92.51 | 97.81 | 95.12 |
| 2007 | 89.12 | 94.42 | 91.74 |
| 2008 | 88.20 | 93.47 | 90.79 |
| 2009 | 89.32 | 94.67 | 91.90 |
| 2010 | 89.50 | 95.20 | 92.29 |
| 2011 | 89.49 | 95.13 | 92.26 |
| 2012 | 86.24 | 92.12 | 89.06 |
| 2013 | 86.96 | 93.05 | 89.86 |
| 2014 | 85.28 | 91.52 | 88.24 |
| 2015 | 82.71 | 89.65 | 86.15 |
| 2016 | 79.39 | 87.94 | 83.68 |
Trend description for D6bi
By 2016, the index of distribution of priority species in England had declined to just under 84, a statistically significant decrease of 16% from its 1970 value. More recently, between 2011 and 2016, the distribution index declined from a little over 92 to just under 84 (by 9% of the 2011 value), again a statistically significant decrease over the latest 5 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. No results are currently available for the medium-term assessment period using the England Biodiversity Indicators methodology, although this will be considered for future publications.
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 4b 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 | -9.31 | 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 | Little or no change | Strong decrease | Strong increase | Weak decrease | Weak increase |
|---|---|---|---|---|---|
| Long term (1970–2016) | 37.57 | 17.13 | 14.92 | 20.99 | 9.39 |
| Short term (2011–2016) | 28.18 | 31.49 | 4.97 | 27.07 | 8.29 |
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 and 24% of species showing an increase in distribution since 1970. The individual results are more unfavourable over the short-term period (2011 to 2016), with 59% of priority species showing a decrease and 13% of species showing an increase in distribution over the latest 5 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.