Official Statistics

Indicators of species abundance in England

Updated 28 April 2026

Applies to England

Last updated: 2026

Latest data available: 2024

Contact

Enquires on this publication to: biodiversity.statistics@defra.gov.uk

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Lead statistician: Clare Betts

Environmental Statistics and Research team
Department for Environment, Food and Rural Affairs
Seacole Building
2 Marsham St
London
SW1P 4DF

Website: Biodiversity and wildlife statistics – Gov.UK

Quick links

• Technical annex
• Published datafile
• Response to feedback
• Frequently asked questions
• Code for running the analysis

Key changes since the last publication

• New modelling work done by the UK Centre for Ecology and Hydrology and the National Plant Monitoring Scheme has enabled us to include several species of plants in the all-species and priority species indicators. Existing plant species in the indicator have also been updated so that their trends are reflective of their England, rather than full UK, abundance. Please see the Technical annex for the full list of species added and for more detail on how these changes have impacted the indicators.
• Following feedback from last year’s release of these statistics (see Response to feedback), we noted that there was no consensus on a preferred smoothing option and so have retained both levels of smoothing this year. Our refreshed plan for moving towards one smoothing option is reflected in the Development Plan.
• We have adjusted the way we calculate short- and medium-term trends, which now involves re-running the models over that specific time period only. This is to avoid biasing these assessments with the long-term trend and is a more statistically appropriate comparison than used previously due to the propagation of uncertainty.
• An all-species distribution index, plus an updated priority species distribution index, has been published as an official statistic in development in the 2025 publication of the England Biodiversity Indicators.

Summary

On average, England’s monitored species have declined markedly since 1970. Average abundance of species in the all-species indicator has fallen by around 40%, and the corresponding priority species indicator has fallen by around 80%. Although the past decade shows some stabilisation for all and priority species, a particularly poor weather year for invertebrates has led to a recent further decline. Many species respond rapidly to weather conditions, so the future trajectory is uncertain. Some groups, like moths, have seen steep long‑term drops, while others such as mammals and vascular plants have fared better. Within each group, individual species show a variety of trends that underlie the overall assessment.

Official statistics in development

This indicator shows changes in the relative abundance of monitored species in England using available monitoring data from 1970 to 2024. As this is an official statistic in development, the Environmental Statistics and Research team welcomes feedback on the novel methods used in the development of this indicator. For example, feedback on whether this new indicator measures something users feel should be measured, any methodological suggestions or on how the statistics are presented and communicated.

Official statistics in development are official statistics that are undergoing a development; they may be new or existing statistics, and will be tested with users, in line with the standards of trustworthiness, quality, and value in the Code of Practice for Statistics.

To give feedback, email the Environmental Statistics and Research team at biodiversity.statistics@defra.gov.uk.

Introduction

This release covers two measures of species abundance in England:

1. ‘All-species’ - which contains all species for which we have suitable data and are listed on Schedule 2 of the Environmental Targets (Biodiversity) Regulations.
2. ‘Priority species’ - which includes only species which are deemed priority species.

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.

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 indicator includes data for 1,185 species, although some of these species are in fact aggregates or groups of multiple species that are difficult to distinguish, as is the case for some freshwater invertebrates. For simplicity, these are all referred to as species for the remainder of the release. Plans for developing the indicator further are detailed in the Development Plan.

The all-species indicator mainly represents species found in terrestrial and freshwater environments. The species list for this indicator was developed with the aim of producing an index to summarise trends in abundance for the broadest possible set of organisms, although the species coverage is limited by data availability. As a result, the indicator reflects changes in trends of the selected species across England which are included on Schedule 2. Given the complexity of producing a combined species indicator on this scale and its importance to the target, we will continue to take a transparent approach and seek advice from experts, stakeholders and users, the outcomes of which will be detailed in future releases.

Priority species are defined as those appearing on the priority species list for England (Natural Environmental and Rural Communities Act 2006 - Section 41). Currently this indicator includes data on 161 of the 940 priority species in England.

For both the all-species and priority species indicators two possible versions of the indicator are presented, one with a greater degree of smoothing applied and one with a lesser degree of smoothing. Smoothing is applied to reveal long-term trends in otherwise noisy data. Greater smoothing may provide a clearer view of the underlying long-term trend, while lesser 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 portray the extent to which these trends are dependent on methodological decisions. We are interested in users’ feedback on both options as part of the ongoing development of the indicator.

This release also breaks these two measures down by taxonomic group. We already publish species abundance indices for birds and butterflies in our Wild bird populations in the UK and England and Butterflies in the UK and England publications, though those publications use different methods for creating composite indices and species coverage varies. Whilst these species groups are included in the indicators presented here, to avoid confusion their taxonomic breakdowns are not included in this publication.

Presented in this publication are indicators 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.

Assessment of change

Table 1: Results from the assessment of change

Measure	Assessment	Time period	Result
All-species	Long term	1970 to 2024	Deteriorating
All-species	Medium term	2014 to 2024	Deteriorating
All-species	Short term	2019 to 2024	Deteriorating
Priority species	Long term	1970 to 2024	Deteriorating
Priority species	Medium term	2014 to 2024	Deteriorating
Priority species	Short term	2019 to 2024	Deteriorating

Note about Table 1:

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. For short- and medium-term trends, the model is re-run across only the relevant time period to make the assessment. This is a change compared to previous short- and medium-term assessments which compared year pairs from the entire time series. The assessment process will be reviewed as part of the ongoing development of these statistics (see Development Plan for more details).

All species

The all-species indicator is based on data for 1,185 species. These are the species listed on Schedule 2 for which suitable data is available. See the Technical Annex for more information about the standards applied for data inclusion.

Between 1970 and 2024 the index of change in relative abundance of species in England declined by around 40% (Figure 1). Over this long-term period 41% of species declined in abundance, while 30% increased (Figure 2).

More recently, between 2019 and 2024, the relative abundance index declined by around 7% (Figure 1). Over this short-term period, 47% of species declined and 38% increased (Figure 2).

Figure 1: The abundance of monitored species in England has fallen on average by around forty percent since 1970

Notes about Figure 1

• Figure 1 shows the two options for the smoothed trend (solid line) with their 95% credible intervals (shaded area). See discussion of smoothing in Caveats and limitations.
• 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 the variation in trends across species, but not uncertainty in the underlying species abundance indices for individual species. They do not capture uncertainty associated with the spatial locations of sample points, nor about the degree to which the species represent non-sampled species.

Figure 2: More species have declined than increased over both the last five years and since 1970)

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 Background and Methodology for more detail).
• Due to rounding, the data labels may not sum exactly to 100%.
• Short term assessments are based on 1,181 species since short term trends are unavailable for 4 species.

Overall, 2024 ranked as the UK’s fourth warmest and eighth wettest year since the early 1900s, but with a cooler than average June, this combination of factors can disrupt seasonal patterns essential to many species, particularly butterflies, moths and bumblebees. It is known that 2024 was a particularly bad year for bumblebees and butterflies. The adverse weather pattern in 2024 will be partially responsible for the sharp drop in the index in 2024. Further discussion on the impact for the individual groups can be found here.

The trend in the headline indicator (Figure 1) over recent years has changed since the previous publication. This is due to the addition of a new year of data for each species, as well as data updates to other recent years of data for some species. The addition and exclusion of a small number of species will also have had a small impact. Variations in weather and climate will also impact species abundance from year to year. Species abundance data is inherently volatile due to the nature of the ecological systems being measured, as well as the methodological and statistical techniques for drawing inferences about those ecological systems. See the Technical Annex for a more detailed comparison between the indicators since last year.

The headline indicator (Figure 1) masks variation between the taxonomic groups which make up the indicator. 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 bird, 11 bumblebee, 55 butterfly, 37 freshwater and estuarine fish, 235 freshwater invertebrate, 17 mammal, 444 moth and 218 vascular plant species. Moths have undergone the biggest decline with an index value in the final year that is only around 43% of its value in 1970, although most of the decline occurred prior to 2000. Only mammals have increased compared to their baseline year, although the credible interval is only marginally above the baseline value, suggesting the increase should be viewed with caution. Freshwater invertebrates, bumblebees, fish and vascular plants have all shown little change compared to their baseline, or have wide credible intervals which reduces confidence in any observed change. We publish species abundance indices for birds and butterflies in our 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 2).

The width of the credible intervals in Figure 3, shown by the shaded area, is determined by several factors. The most important of these being the number of species: groups with many species, such as freshwater invertebrates, moths, vascular plants, have much narrower credible intervals than those with few species, such as bumblebees, fish, and mammals. A second factor is the degree to which the multispecies trend varies over time: credible intervals will be wider for groups where the trend changes direction over time, such as fish, than for groups where the trend is relatively stable, like mammals. A third factor is the length of the trend: because the uncertainty is measured relative to the baseline year, the width of the credible interval grows steadily over time. For example, this may partly explain why the credible interval for moths is wider than the credible interval for freshwater invertebrates.

Figure 3: Long‑term trends vary across species groups, with some rising and others declining

Notes about Figure 3

• Figure 3 shows the two options for the smoothed trend (solid line) with their 95% credible intervals (shaded area) for each taxonomic group. See discussion of smoothing in Caveats and limitations.
• Trends 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 of 100 in the start year for each group. 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 the variation in trends across species, but not uncertainty in the underlying species abundance indices for individual species. They do not capture uncertainty associated with the spatial locations of sample points, nor about the degree to which the species represent non-sampled species.
• Defra publishes species abundance indices for birds and butterflies in the Wild bird populations in England and Butterflies in England publications, so those taxonomic breakdowns are not included in this publication.

Table 2: All-species indicator values broken down by taxonomic group

Taxon	Number of species	Baseline year	Option 1 index value in 2024	Option 2 index value in 2024
Birds	168	1970	-	-
Bumblebees	11	2010	86.9 (63.6-118.2)	86.7 (64.3-118.9)
Butterflies	55	1976	-	-
Fish	37	2000	153.1 (102.6-236.4)	152.2 (99.1-231.8)
Freshwater invertebrates	235	2013	98.6 (94.4-102.8)	98.5 (94.1-102.8)
Mammals	17	1995	115.5 (100.5-133.5)	116.1 (100.5-132.9)
Moths	444	1970	43.7 (38.8-49.5)	43.4 (38.5-48.7)
Vascular plants	218	2015	103.3 (98.8-108.2)	103.2 (98.4-108.4)

Notes about Table 2:

• Defra publishes species abundance indices for birds and butterflies in the Wild bird populations in England and Butterflies in England publications, so those taxonomic breakdowns are not included in this publication.
• Credible intervals for each value are shown in brackets. Where these include the value 100, we conclude that the index for the taxonomic group has shown little or no change since its baseline year.

Species level trends can be further aggregated into taxonomic groups (Figure 4). These groups are ordered by the proportion of strongly declining species in the long term, with bumblebees at 45%, fish at 32% and moths at 27%. In the short term, the patterns of groups in strong decline remain similar to long term patterns, but in general at increased levels. This includes 64% of bumblebees, 51% of fish, 44% of moths and freshwater invertebrates in short-term strong decline. This is contrasted by the increase in the number of strongly increasing species in some groups, including vascular plants, for which 16% of species are strongly increasing in the long term compared to 37% in the short term.

Figure 4: Strong short-term declines can be seen for invertebrates, but with some plants increasing

Notes about Figure 4

• Figure 4 shows the percentage of species within the taxonomic groups of 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 Background and Methodology for more detail).
• Due to rounding, the data labels may not sum exactly to 100%.
• Short term assessments are based on 1,181 species since short term trends are unavailable for 4 species.

Priority species

The priority species abundance indicator draws species observation data for species which are deemed a conservation priority. Priority species are defined as those appearing on the priority species list for England (Natural Environmental and Rural Communities Act 2006 - Section 41). The priority species were highlighted as being of conservation concern for a variety of reasons, including rapid decline in some of their populations. The indicator therefore includes a substantial number of species that, by definition, are becoming less abundant. In England there are 940 species and 3 subspecies on the priority species list, and this indicator shows the average change in the 161 species for which abundance trends are available in England. Most of the 161 species included in this priority species indicator also appear on Schedule 2 and therefore are included in the all-species indicator. A full breakdown of species and their inclusion in the two indicators can be found in the published datafile.

By 2024, the index of change in relative abundance of priority species in England had declined by around 80% since 1970 (Figure 5). Over this long-term period, 17% of species increased and 70% declined (Figure 6).

More recently, between 2019 and 2024, the relative abundance of priority species declined by around 4% (Figure 5). Over this short-term period, 36% of species increased and 54% declined (Figure 6).

Figure 5: The abundance of priority species in England has declined on average by eighty percent since 1970

Notes about Figure 5

• Figure 5 shows the two options for the smoothed trend (solid line) with their 95% credible intervals (shaded area). See discussion of smoothing in Caveats and limitations.
• 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 the variation in trends across species, but not uncertainty in the underlying species abundance indices for individual species. They do not capture uncertainty associated with the spatial locations of sample points, nor about the degree to which the species represent non-sampled species.

Figure 6: More than half of 161 priority species are declining in the long and short term

Notes about Figure 6

• Figure 6 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 Background and Methodology for more detail).
• Due to rounding, the data labels may not sum exactly to 100%.
• Short term assessments are based on 158 priority species since short term trends are unavailable for 3 species.

The unusual weather conditions in 2024 which will have impacted the 2024 estimate of the all-species abundance indicator will have also impacted the priority species abundance indicator.

The headline indicator (Figure 5) masks variation between taxonomic groups. Figure 7 shows the trend for each taxonomic group separately, generated using the same methods as the headline indicator. The relative abundance measure comprises 44 bird species, 21 butterflies, 8 mammals and 76 moths. In 2025 we also added 1 bumblebee, 8 fish, 2 freshwater invertebrates and 1 vascular plant. The moths have undergone the biggest decline with an index value in the final year (2024) that was around just 13% of its value in 1970. Butterflies and birds have also experienced strong declines in 2024, with butterflies having an index value that was roughly 34% of the 1976 baseline, and birds at around 28% relative to the 1970 baseline. The mammal and fish indices have not changed significantly from their baseline values. We do not present breakdowns of the vascular plants, bumblebees or freshwater invertebrates as there are too few species to be representative of these groups.

Figure 7: Most priority groups remain in long-term decline, particularly priority moths, where species have dropped on average to one eighth of their initial abundance

Notes about Figure 7

• Figure 7 shows the two options for the smoothed trend (solid line) together with their 95% credible intervals (shaded area) for each of the four taxonomic groups included in the composite indicator (see discussion of smoothing in Caveats and limitations).
• Index values represent change from the baseline value for each group. 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 the variation in trends across species, but not uncertainty in the underlying species abundance indices for individual species. They do not capture uncertainty associated with the spatial locations of sample points, nor about the degree to which the species represent non-sampled species.
• Priority fish are shown on a different y-axis scale to the other taxonomic groups as the credible intervals almost exceed 1,000.

The priority fish trends have very large credible intervals in places, almost reaching 1,000 in the early 2010’s. This likely reflects the low number of species included (8 priority fish species) and the high proportion of coastal and estuarine species in this group. Recording effort for coastal and estuarine fish species varies more from year-to-year than for freshwater species. Due to the nature of fishing, the data produced tend to be more uncertain than those for other species.

Table 3: Priority species indicator values broken down by taxonomic group

Taxon	Number of species	Baseline year	Option 1 index value in 2024	Option 2 index value in 2024
Birds	44	1970	28.5 (23.0-35.7)	28.6 (22.9-36.1)
Butterflies	21	1976	35.0 (20.4-60.3)	34.5 (20.8-58.3)
Fish	8	2000	140.2 (52.7-387.6)	144.5 (55.8-370.2)
Mammals	8	1998	112.7 (94.2-134.2)	112.7 (94.9-133.9)
Moths	76	1970	12.7 (9.5-16.9)	12.6 (9.5-16.6)

Note about Table 3:

• Credible intervals for each value are shown in brackets. Where these include the value 100, we conclude that the index for the taxonomic group has shown little or no change since its baseline year.
• The priority species indicator also includes 1 vascular plant, 1 bumblebee and 2 freshwater invertebrate species for which we do not present taxonomic breakdowns.

Priority species level trends can be further aggregated into taxonomic groups (Figure 8). These groups are ordered by the proportion of strongly declining species in the long term, which include priority moths at 57%, priority fish at 50% and priority birds at 45%. In the short term, the percentage of priority fish in strong decline has increased to 75% and the percentage of priority butterflies rose from 33% in the long term to 62% in the most recent five years.

Figure 8: Priority moths remain a concern in the long and short term, with high percentages of priority fish and butterflies also strongly declining in the short term

Notes about Figure 8

• Figure 8 shows the percentage of species within the taxonomic groups of 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 Background and Methodology for more detail).
• Due to rounding, the data labels may not sum exactly to 100%.

Discussion

All-species and priority species indicators

Both indicators capture a decline in abundance across species in England since 1970. For the all-species indicator, this trend appears to level around the year 2000, but with a more recent decline to 60% of the 1970 value. Since 1970, 41% of species showed a strong or weak decline, while 30% showed a strong or weak increase. The priority species indicator has declined much further than the all-species, to just under 20% of the 1970 value, but with a similar leveling off period from 2000. There is a similar period of decline at the end of the priority species indicator, although it is not as pronounced as in the all-species trend. Over this long-term period, 70% of priority species showed a strong or weak decline, while only 17% of priority species showed a strong or weak increase.

There are several contributing factors to the differences in the two indicators. Firstly, their taxonomic composition is very different, with many additional species included in the all-species indicator compared to the priority species indicator. The criteria for selection of species were also different. For the all-species indicator, the list includes the broadest range of relevant species for which we have suitable abundance data available. In comparison, the priority species list is based upon species which have been identified as being of conservation concern, many of which are very likely to be those which have already experienced declines.

Change in relative species abundance by taxon

As shown in Figure 4 and Figure 8, different patterns of change were observed between taxonomic groups. Further work is needed to fully explore these changes, but existing publications provide an indication of the drivers of change for specific taxonomic groups. Defra publishes species abundance indices for birds and butterflies in the Wild bird populations in the UK and England and Butterflies in the UK and England publications, so to avoid confusion, those taxonomic breakdowns are not discussed here.

Birds

Detail on the factors affecting different birds species can be found in detail in the Wild Bird publication.

Bumblebees

The bumblebee species included in the all-species indicator initially increased in abundance, then declined to near the baseline value in 2024. The BeeWalk 10-year report (Comont & Dickinson, 2022) describes the impact of changes in weather on bumblebee abundance. This reports a drop in abundance in 2018, likely due to the summer heatwave that year, and a further decline in 2021 as the cold spring hindered colony establishment. Recent changes in abundance are likely to be driven by the heatwave in 2022, as well as the variable weather in 2023 (Comont & Dickinson, 2023). Overall, 2024 was the worst year on record since the BeeWalk scheme began, with lower than average counts of bumblebees recorded. There was some variation among individual species, with declines in those early-peaking species in June/July, such as white-tailed and red-tailed bumblebees, and a mixed picture for late-peaking species with some weather improvements by August. Other drivers of bumblebee declines in England include habitat loss and degradation, use of pesticides, and climate change (Whitehorn et al., 2022). The data included for bumblebee species in these indicators of species abundance are a relatively short time series, which combined with the natural variability in the populations of these species makes it challenging to confidently detect change.

Butterflies

Detail on the factors affecting different butterfly species can be found in detail in our Butterflies publication. In 2024, Butterfly conservation reported the lowest recorded number of butterflies in the Big Butterfly Count, but early indications suggest that there was some recovery for some species in 2025.

Fish

Since 2000, the freshwater and estuarine fish species included in the all-species indicator have steadily increased in abundance up until around 2012, and then declined to near the baseline value in 2024. We are not aware of any existing analysis of the drivers of these abundance trends, but common pressures on freshwater fish include hydromorphological alterations, loss of connectivity, pollution, climate change and invasive species. A recent study assessing freshwater fish in England found that 7 out of the 34 species assessed were classified as threatened with extinction according to IUCN Red List criteria (Nunn et al., 2023). Those under particular threat included the European eel and Atlantic salmon.

Data for freshwater and estuarine fish can be volatile, in part due to shoaling species which tend to either not be found at all at a particular site, or found in very high numbers. This can make it challenging to draw inferences about long- and short-term trends in abundance for some species. In addition to this, the volume of data collection by the Environment Agency has been variable in recent years, in part due to the COVID-19 pandemic.

Freshwater invertebrates

The freshwater invertebrates included in the all-species indicator have shown an initial increase in abundance since 2013 and then a more recent decline to around their baseline level. This aligns with existing evidence for complex, although mostly stable or increasing trends, of freshwater invertebrates in England (Sadykova et al., 2025, Johnson et al., 2026). For example, a recent analysis demonstrated that overall freshwater macroinvertebrate species richness increased throughout England between 1989 and 2018 (Qu et al., 2023). Pharoah et al. (2023) also found an increase in taxonomic richness in English and Welsh river macroinvertebrate communities between 1991 and 2019, with a shift towards more pollution-sensitive taxa over time. These trends may be linked to improvements in water quality in some places, such as reduced concentrations of some pollutants (Whelan et al. 2022). As well as pollution, freshwater invertebrates are impacted by pressures such as hydromorphological alterations, loss of connectivity, climate change and invasive species.

Mammals

The mammal species included in the all-species indicator have shown a slight increase in abundance since 1995, while those in the priority species index have shown little to no change since 1998. Of the 17 mammal species in the all-species indicator, 10 are species of bat. On average bat species in England have increased since 1999 (Widespread bats in England). However, these trends reflect relatively recent changes in bat populations. It is generally considered that prior to this there were significant historical declines in bat populations dating back to at least the start of the 20th century. This suggests that current legislation and conservation actions to protect and conserve bats have had a positive impact. Bats and their roosts have had legal protection since 1981, and all species of bat are protected in England.

Other mammals in the all-species indicator come from a wide variety of taxa, all of which are threatened by human activities, changing habitats and disease, consequently many have shown strong declines (for example hazel dormice and red fox). However, some have shown strong increases, such as brown hare.

Moths

The moth species included in both the all-species and priority species indicators have declined overall since 1970. A large proportion of the moth species in the all-species indicator are macromoths (a very small number are micromoths). The State of Britain’s Larger Moths 2021 (Fox et al., 2021) also reported declines in moth abundance over the long term. The causes of change in moth abundance are not fully understood. Habitat destruction and deterioration remain pressing concerns for moths, driven by land-use change and chemical pollution. Many moths are heavily reliant on particular plant species for their larval life stage, and these plants species themselves will be affected by habitat deterioration and climate change. Artificial light at night has negative effects on moth development and behaviour, but links to population-level decline are yet to be proved. There is also growing evidence of negative impacts of climate change, particularly on moths that are adapted to cooler conditions in northern, western and upland Britain (Fox et al., 2021, Martay et al., 2017).

Vascular plants

The vascular plant species included in the all-species indicator have shown little change overall since 2015. In 2025, the England Biodiversity Indicators reported new trends in the abundance of plant species considered indicative of good habitat condition in England (Plants of the wider countryside). Trends are presented for four broad habitat types: arable field margins; broadleaved woodlands and hedges; bog and wet heath; and lowland grassland. Within each habitat plant species abundance trends considered indicative of good condition are averaged to provide an indication of the habitat’s current state. Since 2015, plant species among:

• Arable field margins is at 105% of the baseline value
• Bog and wet heath is at 95% of the baseline value
• Broadleaved woodland and hedges is at 103% of the baseline value
• Lowland grassland is at 108% of the baseline value

The pressures driving changes in plant species abundance can vary between habitats, but include changes in land use, agricultural practices, and the climate (Walker et al. 2023).

Official statistics in development designation

Our statistical practice is regulated by the Office for Statistics Regulation (OSR). OSR sets the standards of trustworthiness, quality and value in the Code of Practice for Statistics that all producers of official statistics should adhere to. You can read about how Official Statistics in Defra comply with these standards on the Defra Statistics website.

This publication is an official statistic in development. Official statistics in development are official statistics that are undergoing a development; they may be new or existing statistics, and will be tested with users, in line with the standards of trustworthiness, quality, and value in the Code of Practice for Statistics.

Details of how we plan to develop these statistics are laid out in the Development Plan. We particularly welcome feedback from users on the methodology and presentation of the statistics set out in this release, and our future plans for development.

Background and methodology

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, Non-governmental organisations (NGOs), and research organisations, or through statutory monitoring schemes. We have included as many species as possible in these indicators (Table 1 in Technical annex). However, the taxonomic and species coverage is limited by data availability and these measures are, therefore, not fully representative of species in England. See ‘Source data used’ in the Technical Annex for more detail.

Species included

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 species that are included in the indicator, and the methods used to create the species indicator can be found in the Technical Annex.

All-species indicator

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 refer to this as Schedule 2. The indicator does not yet include data for all 1,195 species, as data are not ready for inclusion for a small number of species (1 plant, 8 moths and 1 fish). More details of these species can be found in the Technical annex.

The species included in Schedule 2 were chosen from as wide a range of taxa as possible, where sufficient data existed. 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 breakdown of species and taxa included in the indicator can be found in the published datafile. The number of species included in each year of the index is shown in Figure 2 in the Technical Annex.

Priority species indicator

The species considered for inclusion in the England Priority Species Indicator are those on the Section 41 list, which is based upon species which have been identified as being of conservation concern. Many of these species have already experienced declines. Species on the Section 41 list are those on the 2007 UK Biodiversity Action Plan (UK BAP) list that are present in England with the addition of Hen Harrier. There are a small number of taxa below the species level (that is, sub-species) on the Section 41 lists. Such infra-specific taxa were only retained if the associated species was not included. This led to the removal of three sub-species and reduced the total taxa on the Section 41 list from 943 to 940. However, not all species on that list have suitable data available.

The species in the priority species indicator are those species for which annual estimates of abundance are available, derived from national-scale monitoring schemes. Currently it contains data on 161 species. Six species of moth were excluded from the priority species indicator in 2025, due to the same failure of quality assurance checks in the all-species indicator. These species are: straw belle (Aspiates gilvaria), Haworth’s minor (Celaena haworthii), grey mountain carpet (Entephria caesiata), crescent (Helotropha leucostigma), Scythris siccella and heath rustic (Xestia agathina). One priority species of moth met the threshold for inclusion this year and so has been added to the indicator: barberry moth (Pareulype berberata). As this species did not have enough available data when Schedule 2 was written, it has not been included in the all-species indicator.

Method for creating a composite indicator of species abundance

The method for estimating the change in relative abundance for a group of species is complex and consists of many steps. The key steps taken to produce the estimates are as follows:

1. Collection of observations in the field. Each scheme follows a set of standardised protocols to collect data on species abundance, typically involving counts of individuals across a fixed network of survey locations. In the case of vascular plants, abundance is measured in terms of percentage cover, rather than the number of individuals.
2. Calculation of a national index of abundance for each species in each year. With a few exceptions, this involves the use of statistical methods that were developed specifically for that survey. For most datasets, this step is performed by the schemes that collect the data.
3. Data cleaning to ensure the right species names are used and adjust for any zero counts.
4. Pre-smoothing individual species trends to remove short-term fluctuations and reveal long term trends.
5. Calculation of smooth multispecies (composite) indicator and trends, accounting for missing values.

Steps 1 and 2 vary by monitoring scheme: in most cases the details are published on sampling scheme websites and summarised in Table 2 of the Technical annex. Steps 3, 4 and 5 are covered briefly below, and expanded upon in ‘Model specifics’ in the Technical annex. The code for these steps is available on GitHub.

Data Cleaning

Raw data made available from monitoring schemes need to be cleaned to account for zero counts and standardising taxon names. Further details on these adjustments can be found in ‘Model specifics’ in the Technical annex.

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 statistical smoothing to remove short term stochastic variation. See ‘Model specifics’ in the Technical Annex for more details of how the pre-smoothing was applied and further discussion of the impacts of pre-smoothing in Caveats and limitations.

Multispecies trends

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.

In the model, the user can choose between two different estimates of geometric mean abundance. The Freeman model estimates a shared growth rate across all the species in the model, which is a rate of change between two time points. This growth rate is then used to estimate individual species’ trends and fill in any missing gaps. These two abundance measures are calculated using different methods:

• M: calculated by adding up the shared growth rate, which shows how an average species is changing from year-to-year
• M’: calculated by averaging across all the species’ trends estimated from the model

For this publication we have chosen to present M, rather than M’, as our overall indicator line, as it has greater options for smoothing. See ‘Model specifics’ in the Technical Annex for more details of the Freeman method and how it was applied to these data. The code to run this model is available on GitHub.

Smoothing to reveal long-term trends

Indicators are a summary of distinct species-specific times-series, essentially, an average time-series across a set of species. Indicators inherently lose the granular detail (species-time-series) in favour of a broader picture of patterns of change (see Figure 9). Smoothing, by nature, will also result in a loss of granularity, meaning that strong fluctuations in inter-annual species- or group-specific abundance values, will be down weighted in favour of a smoothed trend. It is standard practice for species trends to be smoothed to reduce the impact of between-year fluctuations, making underlying trends easier to detect, however the manner in which this is achieved varies by recording scheme. There is no existing protocol for smoothing a composite species indicator with as wide a species coverage as those included in these indicators.

A smoothing process is applied within the model (Freeman et al., 2020), using a penalised spline 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.

Figure 9 shows just some of this variability for some of the taxonomic groups in the indicator. As individual species trends are difficult to view for hundreds of species, we show just the taxonomic groups with fewer numbers of species.

Figure 9: The species level indicators that make up each group are highly variable

Notes about Figure 9:

• Figure 9 shows the smoothed trend from Figure 4 (solid line) with its 95% credible intervals (shaded area) compared against the species trends prior to pre-smoothing and input into the final model (lighter lines).
• For brevity, only one of the two smoothing options is shown (option 1, most smoothed) and only the taxonomic groups for which we have data for fewer than 50 species.
• The y-axis has been truncated to 400 to show the variability of trends around the smoothed index, but one species of bumblebee and several species of fish show trends that are considerably higher, contributing to their wider credible intervals.

Assessment of change

Formal assessment of change in the indicators 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 2024), medium-term (the most recent 10 years) and short-term (the most recent 5 years). For short-term and medium-term assessments, the model was re-run on data from the 5 and 10 year time window, respectively.

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 4). 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%).

Table 4: Thresholds used to define individual species’ trends

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

The categorisation of species trends emerges from the multispecies model, rather than from the data which are fed into the model. This is felt to be appropriate, because the multispecies model accounts for missing data and smooths out fluctuations within species with extremely variable trends. A side-effect of this treatment is that a species trend estimate from the all-species indicator model is slightly different from its trend estimate from the priority species indicator model. These differences are minute: the correlation between trends from the different models is extremely high (R squared > 0.999), but in a very small number of cases the difference is enough for species to switch categories. Specifically, one species (European hare) was assigned to different categories in the long-term assessment and three species (greater scaup, belted beauty and Sussex emerald) in the short-term assessment.

Caveats and limitations

Collectively the datasets contributing to the all-species and Priority Species indicators are intermittent (contain missing data) and heterogeneous (they have different properties). There are several examples of creating indices from multiple diverse taxa (for example, the Living Planet Index, the Living Planet Index for the Netherlands, the State of Nature Terrestrial and Freshwater Species Index and Scotland’s Terrestrial Species Abundance Index), but this process still presents some challenges. A particular issue is that short-lived species (for example, insects) tend to fluctuate markedly in abundance from year to year, whereas long-lived species (birds and mammals) do not. This presents a statistical challenge to capture the signal of long-term change amidst the noise of fluctuating population numbers. The generic method described by Freeman et al. (2020) was designed specifically for this situation and has been assessed by independent experts as being appropriate for the task at hand. We intend to publish the independent assessment and will add the link to this publication when available. However, the method might be further refined in future to capture more completely the differences in population fluctuations between taxa.

Representativeness of the indicator

When detecting changes in species abundance, it is important that we can properly understand and communicate how well the samples of data that go into the model reflect the true populations of species in England (Boyd et al., 2022). It is particularly critical when producing multispecies biodiversity indicators from data with a range of sources. These data are seldom available for all species in every relevant location and are often biased in terms of which species, where and when the observation is made. Here, the goal of the all-species indicator is to assess patterns of change in average abundance across all monitored species from Schedule 2 in England from 1970 to the present day. The Schedule 2 list was designed to be representative of broadest possible set of organisms in England where data availability allowed.

The total number of species contributing to the all- and priority-species indicators are reported in Table 1 in the ‘Source data used’ section of the Technical Annex. While the taxonomic coverage of these indicators has improved over time, they rely on data from structured recording schemes so it is restricted to a relatively small subset of taxonomic groups in England. For example, a huge number of insect taxa in England are not represented in these indicators, meaning any inference made to them relies on the large, and likely unrealistic assumption, that these other groups follow patterns of change as seen in those with structured monitoring schemes. At present, the reporting of these two abundance indicators does not provide any clear indication of the representativeness of the sample data in geographic or environmental space (although see the discussion of spatial representation in the ‘Criteria for including source data’ section and ‘Representativeness of the species abundance indicators’ in the Technical annex for more discussion). In future versions of these indicators, and other biodiversity indicators, we would like to provide clear context on the spatial and environmental representation of the sampled data, allowing readers to assess if the sample sites are a good representation of the full distribution of all species included in the indicator.

Taxonomic representation within these indicators was relatively limited prior to mid-2010 (Figure 2 of the Technical annex) and since publication of the early versions of the indicator, we have responded to stakeholder feedback and added further species groups (freshwater invertebrates, fish, vascular plants, bumblebees). These additions improve the overall representativeness of the indicator but result in increased variation in representativeness over time, i.e. many groups lack data in the early part of the time-series. As discussed in ‘Method for creating a composite indicator of species abundance’ section above, the current implementation of the Freeman method assumes the index values of any species with missing data at the start and ends of the series behave in line with the average of all the other species. This is a large and potentially unrealistic assumption. In fact, Figure 8 shows the assumption is likely to be unrealistic given from 2000 onwards, the trend for priority mammals looks very different to the trends for the priority birds or priority moths.

A summary of the species that are, and are not, well represented in the all-species indicator is presented below, and in the data sets accompanying the release of this publication. For more details, please see the ‘Representativeness of the species abundance indicators’ in the Technical Annex. In addition to representation of different species groups, a discussion of how well the indicator represents habitats in England and provision of ecosystem services is also presented.

Species in the indicator

The all-species indicator currently includes a proportionally high number of species of moths, freshwater invertebrates, vascular plants and birds – these groups account for 38%, 20%, 18%, and 14% of the species in the indicator, respectively. The reason for high representation of these groups is that data is collected for a large number of species through well-established monitoring schemes.

Moths are considered to be a useful indicator species for the status of the wider environment (Dar & Jamal, 2021), as they are found in many different habitats across England, are a key part of the food chain for other species like bats and birds and are highly sensitive to environmental change. The all-species indicator includes data for 19% of all moth species in the UK, which makes them less well represented in the indicator than many of the other taxonomic groups. The short life span of moths means that they quickly respond to change, and monitoring their abundance can provide important insights into the impacts of pressures such as agriculture, climate change, pesticides, and pollution. Studies have demonstrated the importance of the pollination services provided by moths across a range of landscapes, including urban and agricultural (Ellis et al., 2023; Walton et al., 2020). Inclusion of moths, as well as butterflies and bumblebees, means that pollination services are partially captured in the indicator (see the Technical Annex for more detail of ecosystem service representation).

Bird species are well represented in the indicator, which includes data for 77% of all bird species in the UK. Bird populations have long been considered to provide a good indication of the broad state of wildlife in England. This is because they occupy a wide range of habitats and respond to environmental pressures that also operate on other groups of wildlife. In addition, there are considerable long-term data on trends in bird populations, allowing for comparison between trends in the short term and long term. Because they are a well-studied taxonomic group, drivers of change for birds are better understood than for other species groups, which enable better interpretation of any observed changes. Birds also have significant cultural importance and are highly valued as a part of the UK’s natural environment by the general public.

Data for vascular plants comes from the National Plant Monitoring Scheme (NPMS), which was designed with the core aim of sampling plant communities within habitats of conservation value. The indicator specifically includes species that have been identified as positive indicators of habitat health, across a range of habitats, making these data a valuable component of the indicator. The indicator includes data for 15% of vascular plant species in the UK.

Invertebrates as an overall group are underrepresented in the indicator, which includes data for butterflies (93% of UK species), moths (19% of UK species), bumblebees (less than 5% of UK bee species), and a range of freshwater invertebrates. Freshwater benthic invertebrates make up 20% of the species in the indicator. The Environment Agency sampling scheme for freshwater benthic invertebrates covers all of England and is done in a systematic way, so we can assume that it reflects the abundance of wider benthic invertebrates. However, we can be less certain that these species represent trends across wider freshwater habitats (see the Technical Annex for more detailed discussion of habitat representation in the indicator).

Species not represented in the indicator

As the indicator is designed to report against a terrestrial target, with the exception of seabirds and a small number of fish living in coastal waters, the indicator does not cover the marine realm.

Notable taxa for which sufficient abundance data is not currently available include fungi, non-vascular plants (bryophytes and algae), microbes, amphibians and reptiles, and terrestrial invertebrates (other than moths, butterflies and bumblebees). Possible changes to the list of species in Schedule 2 may need to be considered and consulted on if sufficient abundance data for these groups become available, meeting the criteria outlined in ‘Criteria for including source data’ in the Technical Annex.

Butterflies are considered to be a good indicator of terrestrial abundance, and inclusion of over 90% of the UK’s butterfly species in the indicator may partially compensate for the poorer representation of other large insect groups. However, we recognise that there are still key gaps and the lack of data for these groups means that some ecosystem services are not well represented in the indicator (particularly decomposition, pest control, and aspects of pollination) – see the Technical Annex for more detail of ecosystem service representation.

Source data limitations

Table 1 of the Technical annex details the datasets used in these indicators, they are generated largely from data collected by national monitoring schemes. In these schemes, data are collected in a robust and consistent manner and the geographical coverage is generally good, however there is variation in the degree to which each dataset is influenced by biases in the sampling protocols, as well as the methods used to account for that.

Most of the datasets that contribute to the indicator derive from national surveillance schemes with a high degree of spatial replication (for number of survey sites – see Table 2 of the Technical annex). These are ideal for producing population time-series for widespread and common species; however, most of these schemes do not generate sufficient sample size to estimate the abundance of difficult to identify, rarer or more range-restricted species. Each scheme has a set of criteria to determine whether time-series can be generated for each species and if they are sufficiently robust to be included in the published results of the scheme. Further information about each monitoring scheme and the data analysis and results can be found on each recording scheme’s website.

A smaller number of datasets derive from targeted surveys of known populations of rare species. In some cases, the data represent complete censuses of the English population (Table 1 of the Technical annex). Thus, the indicator has good representation of common species and, in some groups, of very rare species, but species that are neither very rare nor very common are largely absent (the exception to this is butterflies).

Large national sampling schemes invest significantly in volunteer training, support and resources to enhance the accuracy of species records made by volunteers, many of whom have significant taxonomic skill. All records undergo automated and/or manual verification procedures to “clean” anomalies from datasets before analysis. Many schemes have collected long time-series of data with consistent methods. Where changes to methods have occurred, the effect of these changes on the data series have been investigated to allow continuous trends to be evaluated.

It is known that structured scheme sampling involves bias. Some biases are accounted for in stratified sampling protocols; others are known because the nature of the schemes involves sampling self-selected, high-quality habitats using a set protocol over a long time period. Some bias is less controlled due to the necessity of giving volunteers some choice over where they record, to retain their interest. For example, there is a general trend in schemes for under sampling in more remote and inaccessible areas, some urban areas, and some areas perceived as “less interesting” for example, large homogeneous arable regions. The effect of these biases is less evident in England than other countries of the UK, given a more evenly distributed volunteer population. There is ongoing research and development work within academic institutions into improving the evidence generated from volunteer schemes, including reducing bias in volunteer datasets, enhancing verification methods, and integrating different types of volunteer datasets to better understand species trends at finer spatial scales. As this work develops, findings will be incorporated into these indicators as appropriate.

The values going into the indicator are measures of species abundance at the national scale. The raw data that generate these measures vary from scheme to scheme, reflecting differences in the ecology of the species being monitored. In most cases, the raw data are counts of individual organisms, either from censuses, transect walks or light traps. Some data types are subtly different. For vascular plants, the raw data are measures of percentage cover on a categorical scale within quadrats. For bumblebees, water voles and the field survey of the National Bat Monitoring Program, the data are counts, but not of individuals. In these cases, the survey takes place along a transect route that is split into sections: at each section the presence or absence of each species, for water voles including their signs due to low detectability (Dean et al., 2016), is recorded, and the count used for analysis is the number of sections on which the species was recorded. This method is more appropriate as a measure of abundance than the total number of encounters, either due to the high probability of counting the same individual more than once or, as in the case of water voles, counting multiple signs from the same individual. Counting organisms/signs in this way can be thought of as a measure of local occupancy.

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 clear guidance on the degree to which pairs of years (for example, 2000 versus 2022) differ.

The credible intervals capture uncertainty in the trends between 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 non-sampled species.

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.

Pre-smoothing

Following advice from the Biodiversity Expert Panel, we applied a separate smoothing step to the species abundance indices before creating the composite index (indicator) with the Freeman method. The decision to implement this extra pre-smoothing step was also partly driven by the cross-validation testing which showed an increase in within-dataset predictive accuracy of the Freeman method when applied to a pre-smoothed dataset compared to an unsmoothed dataset. However, following several rounds of feedback it has become apparent that such an approach to assessing predictive accuracy contains several caveats and limitations which are discussed below. Furthermore, other departures from the original implementation of the Freeman method, and consequences thereof, are discussed below.

First, the Freeman method was specifically designed to accommodate unsmoothed input data and any associated short-term variation. Second, the Freeman method is structured to account for the fact that input data provide an imperfect representation of the true underlying state (abundance per year), meaning that individual species-year index values are supplied alongside an estimate of uncertainty (available here for most species from the given input datasets). This uncertainty is then propagated to the final indicator produced by the Freeman method. Note that the current indicator production method departs from both of these original strengths of the Freeman method. The impact of ignoring the species-specific uncertainty is discussed in the ‘Model specifics’ section in the Technical annex, while the impact of pre-smoothing is discussed in the following paragraph.

By design the Freeman method contains two forms of ‘smoothing’. First, growth rates (that is species year to year change) are assumed to follow a log normal distribution parameterised by the data, where the impact of outliers is reduced as they are pulled towards the mean growth rate across species. Second, the Freeman method applies spline-based smoothing at the community (indicator) level which is specifically designed to smooth short-term fluctuations, meaning the indicator better represents the long-term direction of change. These inbuilt smoothing approaches mean that any additional pre-smoothing of the input data should be superfluous.

Further development work is currently underway to examine the validity and impact of the methodological departures from the original implementation of the Freeman method. This is highlighted in the development plan (see Development plan below).

Statistically accounting for missing data

As discussed above, not all species have data for every year of the indicator. These species are described as missing rather than truly absent, as they could be undetected by the current sampling strategy. Therefore, it is necessary to account for missingness using statistics, which means making an assumption about the behaviour of species that are missing. In this case, we assume that trends among missing species follow the same overall distribution as those with data. In other words, we assume that species are missing at random.

In reality, this is not true because missingness is mostly a function of when individual datasets start and finish. Many of the datasets in the all-species indicator started after the year 1995 (Figure 2 and Table 1 of the Technical annex): most of the change in the indicator pre-date this time, so our estimates of long-term change reflect historical trends in birds, butterflies and moths.

Another limitation is that some datasets finish earlier than others. In the current publication, most of the species with missing data for 2024 are rare species and/or of conservation concern (rare birds, wetland birds, seabirds, bats and priority moths). The index values for the years 2023 and 2024 should therefore be seen as provisional, reflecting assumptions about the 53 species in the all-species indicator (4.5% of the total) whose trend data has not yet been updated.

It is worth noting that any assumption about data missingness is likely to be problematic: in a previous version of the priority species indicator, it was assumed that species whose time-series ends early would remain fixed at constant abundance, which is likely to lead to an overly optimistic view of short-term trends. In comparison, in the current methodology they are assumed to follow the average pattern of the other species in the indicator.

Development since the previous publication

In the 2025 publication, we said we would continue to investigate the impact of different levels of smoothing in the indicator and make a decision on whether we will continue to produce multiple options for different uses, or produce a single indicator of species abundance, and priority species abundance, in England. Following feedback received on the 2025 publication, we noted no consistent preference on which version of the smoothing is best and have made the decision to retain both at present. Shorter term smoothing (over a three-year cycle) may be more sensitive to interannual variability, whereas longer term smoothing (10 years) may be more useful for considering targets.

We developed and published an indicator of all-species distribution in England, which, alongside the priority species distribution indicator, was published in December 2025. These indicators are published as official statistics in development, following recent changes to the methodology of these indicators.

We have made available the code for all stages of the modelling pipeline on GitHub.

A series of key methodological developments are currently being explored and some progress has been made this year:

• In this publication we have broken down the trend by taxonomic group only. We have explored options for classifying species into habitats where they can be found, so that we could provide a habitat breakdown as in our bird and butterfly indices. This exploration has found that there is no single method available that covers all species in the indicator and no unified modelling approach that could be used without further development. Furthermore, it is unlikely that a single modelling approach would give robust outputs for all species, and would therefore need to be tailored to different species groups and/or supplemented by alternative approaches. Work on further breakdowns will continue.
• We have investigated various methodological decisions and the impact they have on the output. This includes propagation of species-specific uncertainty, pre-smoothing and the assumption that species with missing data behave in a similar way to those with data present in the model. These investigations are currently ongoing and the recommendations will be implemented and discussed in further detail in future versions of this release.
• We have reviewed our methods for assessing change over short and medium time-scales in the indicators. A new approach has been developed that involves re-running the Freeman model on data shortened to the window of interest (most recent 5 years for short term trends and 10 years for medium term trends). We have implement this approach in the current release, which weas recommended as an alternative to re-basing the index to the 5 or 10 year mark, as it will avoid influence of the earlier composition and hindcasting where many species trends are not available in the earlier part of the timeseries.

Development plan

Developments planned over the next two years:

• Revisit the pre-smoothing step in the modelling pipeline and consider alternative options, such as using unsmoothed species’ trends with post-hoc smoothing.
• Implement recommendations surrounding the incorporation of species-specific uncertainty to the model.
• Build upon independent work investigating assessment methods for the statutory targets.
• Improve how we communicate uncertainty in the release, for example, using risk-of-bias assessments, sensitivity analysis or diagnostics on missing data.

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 includes 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 monitor the quality of the raw data and improve the methodology, in line with our commitment to the Code of Practice for Statistics.
• We will work towards developing an indicator for the abundance of all-species at the UK scale.
• In this publication 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 or widespread and rare species).
• We will continue to refine how the methodology is implemented and explore the impacts of any differences from the original Freeman implementation.
• We will continue to review how we communicate the representativeness of the indicator. We will assess the spatial, taxonomic and temporal coverage of the data underlying the indicators and communicate these alongside the indicators. We would also like to explore the trade off between increasing the representativeness of the indicator against our ability to detect meaningful biological change.
• We will review our methods for assessing change over short and medium time-scales in the indicators and, if appropriate, refine them further.

Acknowledgements

Thank you to the many people and organisations who have contributed by providing data, the independent expert review panel who provided useful insights into developing the method and to the many colleagues who have helped produce these indicators.

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