Accredited official statistics

Status of all-species: relative abundance

Updated 10 December 2024

Applies to England

© Crown copyright 2024

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This publication is available at https://www.gov.uk/government/statistics/england-biodiversity-indicators/status-of-all-species-relative-abundance

Last updated: 2024

Latest data available: 2022

Introduction

This indicator shows changes in the relative abundance of all species in England for which suitable data are available. The all-species indicator mainly represents species found in terrestrial and freshwater environments. The all-species indicator was developed with the aim of producing an index to summarise trends in abundance for the broadest possible set of organisms that are representative of English biodiversity, although the species coverage is limited by data availability. Presented in this indicator are values of abundance relative to the starting year (set to a value of 100), rather than absolute abundance. Changes to this value reflect the average change in species abundance; if on average species experienced a doubling in abundance, the indicator would rise to 200, if they halved it would fall to a value of 50.

First published in Indicators of species abundance in England publication, the method for calculating this indicator is not yet finalised and two smoothing options are presented. When fully developed, the all-species abundance measure will be used to track the government’s progress towards meeting the statutory target of halting the decline in species abundance by 2030, and then reversing these declines by 2042. Currently this measure includes data for 1,177 species, plans for developing the indicator further are detailed in the Development Plan.

Data for this indicator can be found in the published datafile.

Type of indicator

State indicator

Type of official statistics

Official statistics in development – indicator under development: The England biodiversity indicators project team would welcome feedback on the novel methods used in the development of this indicator, please email us. For more information, please visit the UK Statistics Authority’s website on Types of official statistics – UK Statistics Authority.

Assessment of change

Measure Assessment Time period Result
All species Long term 1970 to 2022 Deteriorating
All species Medium term 2012 to 2022 Little or no overall change
All species Short term 2017 to 2022 Little or no overall change

Key results

The all-species indicator draws on data for 1,177 species for which we have suitable data. See the Technical annex for more information about the standards applied for data inclusion.

By 2022, the index of change of relative abundance of species in England had declined to 69% of its 1970 value. Over this long-term period 37% of species showed a strong or weak decline, while 34% showed a strong or weak increase.

More recently, between 2017 and 2022, the relative abundance index did not change significantly, changing from 64 in 2017 to 69 in 2022. Over this short-term period, 48% of species showed a strong or weak increase and 37% showed a strong or weak decline.

Figure 1: Change in the relative abundance of all species for which we have data in England, 1970 to 2022

Source: Bat Conservation Trust, Bees, Wasps and Ants Recording Society, Botanical Society of Britain and Ireland, British Trust for Ornithology, Bumblebee Conservation Trust, Butterfly Conservation, Defra, Environment Agency, Joint Nature Conservation Committee, Natural England, NatureScot, Natural Resources Wales, Northern Ireland Environment Agency, People’s Trust for Endangered Species, Plantlife, Queen Mary University of London, Rare Breeding Birds Panel Secretariat, Rothamsted Research, Royal Society for the Protection of Birds, UK Centre for Ecology & Hydrology, University of Kent

Notes about Figure 1

  • Figure 1 shows the two options for the smoothed trend (solid line) with their 95% credible intervals (shaded area).
  • Index values represent change from the baseline value in 1970, the credible interval widens as the index gets further from the 1970 value and confidence in the estimate of change relative to the baseline falls.
  • The credible intervals capture uncertainty in the trends of individual species that contribute to the index. They do not capture uncertainty associated with the spatial locations of sample points, nor about the degree to which the species represent wider biodiversity. The credible intervals partially capture uncertainty in the species abundance estimates.
  • Several different levels of smoothing were considered, with Option 1 being smoothed on a ten-year timescale and Option 2 being smoothed on a three-year timescale (see discussion of smoothing in Technical annex).

Source: Bat Conservation Trust, Bees, Wasps and Ants Recording Society, Botanical Society of Britain and Ireland, British Trust for Ornithology, Bumblebee Conservation Trust, Butterfly Conservation, Defra, Environment Agency, Joint Nature Conservation Committee, Natural England, NatureScot, Natural Resources Wales, Northern Ireland Environment Agency, People’s Trust for Endangered Species, Plantlife, Queen Mary University of London, Rare Breeding Birds Programme Secretariat, Rothamsted Research, Royal Society for the Protection of Birds, UK Centre for Ecology & Hydrology, University of Kent

Notes about Figure 2

  • Figure 2 shows the percentage of species within the indicator that have increased (weakly or strongly), decreased (weakly or strongly) or shown little change in abundance based on set thresholds of change (see [Methodology] for more detail).
  • Due to rounding, the data labels may not sum exactly to 100%.
  • There are seven species for which a short term assessment of change isn’t available.

Further detail

The headline indicator (Figure 1) masks variation between the taxonomic groups. Figure 3 shows the index for each taxonomic group separately, generated using the same methods as the headline indicator. The relative abundance measure comprises 168 birds species, 16 mammals, 37 fish, 55 butterflies, 446 moths, 11 bumblebees, 235 freshwater invertebrates and 209 vascular plants. The moths have undergone the biggest decline with an index value in the final year (2022) that was only 56% of its value in 1970, although most of the decline occurred prior to 2000. Fish, freshwater invertebrates, mammals and vascular plants have all increased since the baseline year (2000, 2013, 1995 and 2015 respectively). Bumblebees have shown little change compared to their baseline year (2010). Defra already publish species abundance indices for birds and butterflies in its Wild bird populations in England and Butterflies in England publications, so those taxonomic breakdowns are not included in this publication. Data collection for each taxonomic group spans different time periods and so the baseline year for each differs (see Table 1, Technical annex).

Figure 3: Change in relative species abundance by taxonomic group, 2000 to 2022

Source: Bat Conservation Trust, Bees, Wasps and Ants Recording Society, Botanical Society of Britain and Ireland, British Trust for Ornithology, Bumblebee Conservation Trust, Butterfly Conservation, Defra, Environment Agency, Joint Nature Conservation Committee, Natural England, NatureScot, Natural Resources Wales, Northern Ireland Environment Agency, People’s Trust for Endangered Species, Plantlife, Queen Mary University of London, Rare Breeding Birds Programme Secretariat, Rothamsted Research, Royal Society for the Protection of Birds, UK Centre for Ecology & Hydrology, University of Kent.

Notes about Figure 3

  • Figure 3 shows the two options for the smoothed trend (solid line) with their 95% credible intervals (shaded area).
  • Included in Figure 3 are 168 bird species, 11 bumblebee species, 55 butterfly species, 37 freshwater and estuarine fish, 235 freshwater invertebrates, 16 mammals, 446 moths, and 209 vascular plants.
  • Indices for the years prior to the year 2000 are not shown as data for many individual groups are not available prior to that year.
  • Index values represent change from the baseline value for each group; in 2010 for bumblebees, 2000 for fish, 2013 for freshwater invertebrates, 1995 for mammals, 1970 for moths and 2015 for vascular plants. The credible interval widens as the index gets further from the baseline value and confidence in the estimate of change relative to the baseline falls.
  • The credible intervals capture uncertainty in the trends of individual species that contribute to the index. They do not capture uncertainty associated with the spatial locations of sample points, nor about the degree to which the species represent wider biodiversity. The credible intervals partially capture uncertainty in the species abundance estimates.
  • Several different levels of smoothing were considered, with Option 1 being smoothed on a ten-year timescale and Option 2 being smoothed on a three-year timescale. For Option 1, there were several groups where the timeseries was too short to allow for smoothing over ten years: these have been smoothed to the maximum number of years possible (4 years for vascular plants, 5 years for freshwater invertebrates and 6.5 years for bumblebees).
  • Defra already publish species abundance indices for birds and butterflies in their Wild bird populations in England and Butterflies in England publications, so those taxonomic breakdowns are not included in this publication.

Relevance

Monitoring the abundance of species is important for our understanding of the state of the wider environment, particularly as measures of species abundance are more sensitive to change than other aspects of species populations. It should be noted that for a more comprehensive indication of the state of the wider environment, indicators of species abundance should be reviewed alongside species distribution and extinction risk indicators.

International/domestic reporting

When fully developed, the all-species abundance measure will be used to track the government’s progress towards meeting the Environmental Improvement Plan 2023 statutory targets for biodiversity on land. The target seeks to halt the decline in species abundance by 2030, and by the end of 2042, reverse the decline so that species abundance is higher than in 2022 and at least 10% higher than in 2030.

This indicator feeds into the Outcome Indicator Framework, a set of indicators describing environmental change related to the ten goals within the 25 year Environment Plan. As part of the Outcome Indicator Framework, this data contributes towards the evidence base used to prepare the annual progress report for the Environmental Improvement Plan. This indicator contributes to OIF indicator D4: Relative abundance and/or distribution of species.

Acknowledgements

Thank you to the many people who have contributed by providing data and to the many colleagues who have helped produce this indicator.

Technical annex

For a more in-depth discussion of the methodology and data used in this indicator, please see Indicators of species abundance in England. A brief summary of these is presented in the following.

Source data

Much of the data on species abundance is collected through well-established volunteer-based recording schemes, many of which are run through partnerships between government bodies, NGOs and research organisations, or through statutory monitoring schemes. The species have not been selected as a representative sample of species and they cover only a limited range of taxonomic groups. The measure is therefore not fully representative of species in the wider countryside (see Species included).

Three criteria were used to assess whether data was suitable for inclusion in the indicator: that the scheme uses a standarised approach with protocols and appropriate analytical methods, has spatially replicated survey design across England and a taxonomic resolution ideally to species level. More details on these criteria can be found in the full statistical release

Robust English population time-series were sought for as many species as possible to produce the indicator for All Species in England. The measure is a composite indicator of 1,177 species from 4 broad taxonomic groups. The majority of the data in this indicator have previously been published and many of the datasets are currently used elsewhere within the England biodiversity indicators. Table 1 presents the taxonomic coverage and data sources contributing to the indicator. Further information on the analytical methods used by each scheme can be found here.

Table 1: Summary of information on the data collection schemes included in the indicators

Name of scheme Taxonomic coverage Number of species in all-species indicator Timespan included in indicators
Breeding Bird Survey (BBS) Birds 95 1970-2022
Rare Breeding Birds Panel (RBBP) Birds 33 1970-2021
Seabird Monitoring Programme (SMP) Birds 12 1986-2019
Statutory Conservation Agency and RSPB Annual Breeding Bird Scheme (SCARRABS) Birds 8 1971-2016
Wetland Bird Survey (WeBS) Birds 20 1975-2021
BeeWalks Bumblebees 11 2010-2022
UK Butterfly Monitoring Scheme (UKBMS) Butterflies 55 1976-2022
National Fish Population Database (NFPD) and Transitional/Coastal waters Data (TRaC) Fish 37 2000-2022
Freshwater Invertebrates (BIOSYS) Freshwater invertebrates 235 2013-2022
Breeding Birds Survey (BBS) Mammals Mammals 5 1995-2022
National Bat Monitoring Programme (NBMP) Mammals 10 1998-2021
National Dormouse Monitoring Programme (NDMP) Mammals (single species) 1 1995-2022
Priority Moths Moths 11 1995-2021
Rothamsted Insect Survey Light Trap Moths 435 1970-2022
National Plant Monitoring Scheme (NPMS) Vascular plants 209 2015-2022

Notes about Table 1:

  • The Breeding Bird Survey began in 1994 and incorporates the Waterways Breeding Bird Survey and the Heronries Census. Prior to this, data came from the Common Bird Census (CBC).

Species included

The species in the all-species indicator are intended to be as representative as possible of wider biodiversity in England, although the coverage is limited by the availability of data from existing monitoring schemes (Table 2). All native and naturalised species with suitable data were considered for inclusion in the indicator. Invasive non-native species were excluded. All species that were naturalised before 1500 were included, as well as those that colonised England from mainland Europe more recently (for example, the tree bumblebee Bombus hypnorum which arrived in England from Europe in 2001).

The vast majority of the 1,177 taxa in the all-species indicator are individual species. There are 20 species groups and 66 genera – the majority of these species groups and genera are from the freshwater macroinvertebrate dataset. This reflects the fact that many invertebrates are difficult to identify to species level, especially in their larval stage. The decision to include these higher taxa reflects the desire for the indicator to be broadly representative.

The species in the all-species indicator align with those listed in Schedule 2 of The Environmental Targets (Biodiversity) (England) Regulations 2023, which sets out 1,195 species that should be monitored as part of the species abundance targets. Throughout the rest of this publication we will refer to it as Schedule 2. The indicator does not yet include data for all 1,195 these species, as data are not yet ready for inclusion for a small number of species (10 plants, 6 moths, 1 fish and 1 mammal).

Table 2: Taxonomic groups included in the all-species species indicator and their representativeness of UK biodiversity

Higher group Group Number of species in the UK Species included in all-species abundance indicator
Vertebrates Amphibians 7 -
Vertebrates Birds 218 168
Vertebrates Fish 82 37
Vertebrates Mammals 49 16
Vertebrates Reptiles 6 -
Invertebrates Coleoptera (beetles) 4,093 34
Invertebrates Butterflies 59 55
Invertebrates Hymenoptera (bees, ants, wasps) 7,154 11
Invertebrates Moths 2,345 446
Invertebrates Diptera (flies) 7,099 25
Invertebrates Other insects 3,197 132
Invertebrates Non-insect invertebrates 5,369 44
Plants Vascular plants 1,497 209
Plants Bryophytes 1,056 -
Plants Chlorophyta 2,342 -
Fungi Non-lichenised fungi 15,100 -
Fungi Lichens 2,354 -
Total - - 1177

Notes about Table 2:

  • An indicative list of species was only available for the whole of the UK (Burns et al., 2018), rather than for England specifically. The total number of multicellular eukaryotic freshwater and terrestrial species found in the UK is approximately 55,000, as reported in Burns et al., 2018.

Methodology

Pre-smoothing

Species abundance of many organisms tends to fluctuate from one year to the next. These fluctuations make it difficult to reveal the underlying trends. For this reason, some schemes include a statistical smoothing to remove short term stochastic variation. We therefore applied a smoothing term to each species time series, except those for which a smoothed trend was already available (bats and most of the birds). We applied a thin plate spline with 0.3 degrees of freedom for each data point (Fewster et al., 2000) and did this on the log scale. The resultant smoothed trends were then taken forward to the next stage of analysis.

To create the composite index, we used a method specifically developed for creating multispecies indicators from heterogeneous data (Freeman et al., 2020). The resulting index is an estimate of the geometric mean abundance. This is a relatively newly developed method and offers some advantages over older techniques: it is adaptable to different data types and can cope with the issues often presented by biological monitoring data, such as varying start dates of datasets and missing values.

A smoothing process is used to reduce the impact of between-year fluctuations - such as those caused by variation in weather - making underlying trends easier to detect. For this a penalised spline was used with the number of “knots” set to one of two values. Firstly, as has been done for previous iterations of the priority species indicator and as is standard elsewhere (Fewster et al., 2000), we used the total number of years of data divided by 3. Secondly, in order to reveal a more stable long-term trend in the data, we used the total number of years of data divided by 10. These two values were selected to demonstrate the range of plausible indicator values for the purposes assessing meaningful change in species abundance over time.

The overall trend shows the balance across all the species included in the indicator. Individual species within each measure may be increasing or decreasing in abundance (Figure 2). Estimates will be revised when new data or improved methodologies are developed and will, if necessary, be applied retrospectively to earlier years. Further details about the methods used to create the species indicator can be found in the full statistical release.

Confidence and uncertainty

The credible intervals around the multispecies index represent confidence in the degree to which average abundance in any given year is different from the baseline year (1970). They do not provide a clear guidance on the degree to which pairs of years (for example, 2000 versus 2022) differ.

The credible intervals capture uncertainty in the trends of individual species that contribute to the index. They do not capture uncertainty associated with the spatial locations of sample points, nor about the degree to which the species represent wider biodiversity. The credible intervals partially capture uncertainty in the species abundance estimates, inasmuch as the method includes a term to estimate measurement error. However, our approach does not explicitly propagate information about relative uncertainty of different species or years.

Assessment of change

Formal assessment of change is made on the basis of credible intervals for the time period; if the indicator value for the first year falls outside of the credible intervals for the final year then the indicator is deemed to have changed over that time period. This was done for three time periods; long-term (from the beginning of the time series to 2022), medium-term (the most recent 10 years) and short-term (the most recent 5 years).

To illustrate the variation in trends among individual species, an assessment of change is made for each species. Species are categorised into one of five categories on the basis of defined thresholds (Table 3). The five trend thresholds are based on average annual rates of change over the assessment period and are derived from the rates of decline used to assign species to the red and amber lists of Birds of Conservation Concern (Eaton et al., 2015). Asymmetric percentage change thresholds are used to define these classes as they refer to proportional change, where a doubling of a species index (an increase of 100%) is counterbalanced by a halving (a decrease of 50%).

Category Threshold Long term change
Strong increase An increase of more than 2.81% per annum Equivalent to an increase of more than 100% over 25 years
Weak increase An increase of between 1.16% and 2.81% per annum Equivalent to an increase of between 33% and 100% over 25 years
Little change Change is between +1.16 % and -1.14% per annum Equivalent to a change of between +33% and -25% over 25 years
Weak decrease A decrease of between 1.14% and 2.73% per annum Equivalent to a decrease of between 25% to 50% over 25 years
Strong decrease A decrease of more than 2.73% per annum Equivalent to a decrease of more than 50% over 25 years

Development plan

Developments planned for this indicator follow broadly the plans for the full statistical release. Over the short term, these plans include:

  • We will work towards selecting the most appropriate smoothing option and producing a single indicator of species abundance in England. We particularly welcome user feedback on the two options presented in this indicator.
  • We will develop an indicator of all-species distribution in England.

Longer term development plans:

  • We will review on an ongoing basis new species abundance data that may become available.
  • We will continue to review the data that feeds into the indicator. This will include ongoing review of the status of monitoring schemes (including the schemes that provide data that is used in the current indicator, as well as those that may provide new abundance data in future).
  • We will continue to review the representativeness of the indicator. This will include reviewing how well the indicator represents the species groups that are already included in the indicator, as well as identifying opportunities to improve our evidence where there are specific gaps.
  • In this indicator we have broken down the trend by taxonomic group only. In future, we will explore further options for breakdowns that may be useful for users of the statistic (for example, separate trends for generalist and specialist species).
  • We will work towards developing an indicator for the abundance of all-species at the UK scale.
  • We will review our methods for assessing change over short and medium time-scales in the indicators and, if appropriate, refine them further.
  • We will continue to improve the quality of the raw data, representation of the indicator, and methodology, in line with our commitment to the Code of Practice for Statistics.

We are keen to hear from our users about these plans, as well as our published development plan, please email us.

References

  • Burns, F., Eaton, M.A., Hayhow, D.B., Outhwaite, C.L., Al Fulaij, N., August, T.A., Boughey, K.L., Brereton, T., Brown, A., Bullock, D.J., Gent, T., Haysom, K.A., Isaac, N.J.B., Johns, D.G., Macadam, C.R., Mathews, F., Noble, D.G., Powney, G.D., Sims, D.W., Smart, S.M., Stroh, P., Walker, K.J., Webb, J.R., Webb, T.J., and Gregory, R.D. (2018). An assessment of the state of nature in the United Kingdom: A review of findings, methods and impact. Ecological Indicators, 94(1), 226 to 236. doi.org/10.1016/j.ecolind.2018.06.033
  • Eaton, M. A., Burns, F., Isaac, N. J. B., Gregory, R. D., August, T. A., Barlow, K. E., … Williams, J. (2015). The priority species indicator: measuring the trends in threatened species in the UK. Biodiversity, 16(2–3), 108–119. https://doi.org/10.1080/14888386.2015.1068222
  • Fewster, R M., S T. Buckland, G M. Siriwardena, S R. Baillie, and J D. Wilson (2000). Analysis of Population Trends for Farmland Birds Using Generalized Additive Models. Ecology 81, 1970–84.
  • Freeman, S. N., Isaac, N. J. B., Besbeas, P., Dennis, E., B. and Morgan, B, J., T. (2020) A Generic Method for Estimating and Smoothing Multispecies Biodiversity Indicators Using Intermittent Data. Journal of Agricultural, Biological and Environmental Statistics, 26, 71 to 89. doi.org/10.1007/s13253-020-00410-6
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