Official Statistics

Indicators of species abundance in England: Frequently asked questions

Updated 24 April 2025

Applies to England

Last updated: 2025

Different results to earlier versions of a measure of species abundance

Why does this statistic look different to the version published in 2024?

There are several reasons why the indicators published in 2025 will look slightly different to that published in 2024:

• Some species have been either added or removed from the indicators. This year we added water vole (Arvicola amphibius) to the all-species and priority species indicators. Water vole is already on Schedule 2 and data from the National Water Vole Monitoring Programme was found to meet the standards set for data inclusion. Concerns over the quality and availability of data for a couple of species of moth has meant that the following species have been dropped from the all-species and priority species trends: Aspiates gilvaria and Scythris siccella. One moth, Pareulype berberata, now has enough data for inclusion into the priority species indicator and so has been added this year. This species does not appear on Schedule 2 and so is excluded from the all-species indicator. Last year we also reported several species for which we had data in the all-species index which could be added to the priority species index. This included 1 species of bumblebee, 8 fish, 2 freshwater invertebrates and 1 vascular plant. These have now been added to the priority species index.
• Additional data is available for the most recent years of the indicator, including for the year 2023 and for some species groups, such as the fish, additional data to other years in the timeseries.
• There could have been population changes to the underlying species trends. Given the additional data available, the changes in the indicator could reflect real changes in the species that contribute to the overall trend. However, the short-term trend was assessed as little or no change due to the large credible intervals around the indicator, the same as in last year’s publication, so we cannot be confident that these are meaningful changes. Instead, small differences could be a result of the stochastic nature of the model, which will produce a very slightly different output each time it is run, or uncertainty in the variation in trends across species.

It is important to note that the abundance trend published this year is not final. Due to routine time lags in data from various monitoring schemes becoming available, the time series for some species included in the indicator terminates before 2023. This means that the data points across the time series will continue to be revised in future releases until data from all sources is available. In addition, the indicator is being published as an Official Statistic in Development to encourage further feedback from users and experts that may help to improve further releases. This could include improvements to the methodology that may result in further revisions in future releases and lead to changes to the current trends.

Background to the species abundance target

What is the species abundance target?

The species abundance target requires government to halt species decline by 2030 (relative to 2029). The long-term target requires us to improve species abundance by at least 10% relative to 2030 by 2042.

What is the species abundance indicator?

‘Indicators of species abundance in England’ covers two measures of species abundance; the first which contains all species for which we have suitable data, the second for only those species which are deemed priority species. When fully developed, the all-species abundance measure will be used to track the government’s progress towards meeting the statutory species abundance targets. The all-species indicator tracks changes in the relative abundance of widespread and priority species that exist in a range of habitat types in England.

Why are the target and indicator based on species abundance?

A range of options were explored during the target setting process, and decisions were informed by discussions between Defra, Natural England, the Joint Nature Conservation Committee (JNCC), members of Defra’s Science Advisory Council and the Biodiversity Targets Advisory Group, as well as available research.

Data for species can be presented in many ways to represent different aspects of species populations (for example, species abundance, species distribution, species richness, species extinction risk). The number of species that can be assessed varies between these measures – for example, due to data availability, a larger number of species can be included in distribution indicators than in abundance indicators. Measures of species abundance are the most sensitive to change, which is useful in demonstrating whether policy actions are leading to improvements (especially over the timescale of the 2030 target). It was this sensitivity that resulted in abundance being recommended for the targets, over measures of distribution.

Species abundance is a good proxy for wider ecosystem health, and the ambitious species abundance targets will be achieved through wide-ranging actions to deliver nature recovery. These will include actions to create and restore a range of habitats and to reduce pressures, such as water pollution.

The abundance targets are not intended to be viewed in isolation and should be considered alongside the wider targets for the environment. The Environment Act includes biodiversity targets to restore and create 500,000 hectares of wildlife-rich habitat, and to reduce the risk of species extinction. These are in addition to wider environmental targets under the Environment Act, including on marine protected areas, tree planting, air quality and water quality. Similarly, the abundance indicator should be considered alongside the wider suite of biodiversity indicators published by Defra, including those reported under the England Biodiversity Indicators and the Outcome Indicator Framework for the 25 Year Environment Plan. Taken together, these will help to provide a more holistic picture of the state of nature.

What is the difference between the species abundance indicator, Defra’s other biodiversity statistics and the Outcome Indicator Framework for the 25 Year Environment Plan?

“Indicators of species abundance in England”, is a relatively new addition to Defra’s existing suite of biodiversity and wildlife statistics, which includes the flagship Accredited Official Statistics compendiums Biodiversity Indicators for England and the UK. The Biodiversity Indicators are published annually towards the end of each year and bring together a wide range of measures covering protected areas, habitats, different groups of species, genetic diversity, public awareness, funding for biodiversity and more.

The new indicators of species abundance (all-species and priority species) are also incorporated into the England Biodiversity Indicators compendium. To ensure the data are available as soon as it is ready, in line with the Code of Practice for Statistics, we plan to update the “Indicators of species abundance in England” release on an annual basis each Spring.

The Outcome Indicator Framework is a set of 66 indicators that describe environmental change across different aspects of the environment. This Framework spans beyond biodiversity but draws on some of the Biodiversity Indicators where appropriate. For example, both the priority species abundance indicator, and the all-species abundance indicator appear in the Outcome Indicator Framework (D6: Relative abundance and distribution of priority species in England) and the new all-species measure will be used to replace the interim measures used for D4: Relative abundance and/or distribution of widespread species. The Outcome Indicator Framework is currently updated annually in May to reflect latest available data.

Scientific rigour of the indicator

How did you decide what data was included in the indicator?

The indicator was developed alongside development of the biodiversity targets, 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. Defined criteria were used to assess whether data were suitable for inclusion in the indicator. These ensure that abundance data come from monitoring schemes with standardised approaches, and with sufficient spatial replication across England, to provide confidence that the trends accurately reflect the national status of each species. We have set out more detail on these in the statistics release.

Following development of the first version of the indicator, further work was completed to improve the representativeness of the indicator. Stakeholders and experts (including Defra’s Biodiversity Targets Advisory Group) recommended further exploration of representativeness of the indicator and potential to broaden species coverage, particularly to address the lack of representation of plants and freshwater ecosystems. As a result, work was done to include data for vascular plants and freshwater invertebrates. More information on these initial versions of the indicator is available in the Biodiversity Targets Consultation Evidence Pack.

Following a consultation of the biodiversity targets in 2022, a review of the data included in the indicator, including new data sources, was carried out. The aim of this review was to expand the species coverage of the indicator, and improve its representation of species groups, habitats, and ecosystem services. As a result, additional species were considered to have suitable data to be added to the indicator and a number of species were also removed due to a range of reasons (including species with insufficient data, and two with invasive status). The outputs of this review informed the list of species in Schedule 2 of The Environmental Targets (Biodiversity) (England) Regulations 2023.

The version of the indicator published in 2024 onwards includes data for as many of the species in Schedule 2 as possible. There are a small number of species that we have not been able to include data for– we are working to prepare these data for inclusion in future updates.

Some taxonomic groups don’t have records going back to 1970. How does the indicator deal with differing coverage?

Many of the schemes contributing data to the indicator start at different points in time, so the number of species with data has grown steadily over time. In addition, due to routine time lags in data from various monitoring schemes becoming available, the time series for some species included in the indicator terminates early.

The method used to produce the abundance indicator was specifically developed to be able to handle missing data. Species with missing data at the start (or end) of the overall time series are assumed to behave in line with the average of all the other species that do have data for those years. More detail of the method, and how it handles missing values, is set out in the statistics release.

Why have you used smoothing within the statistic?

It is standard practice for species trends to be smoothed to reduce the impact of between-year fluctuations, such as those caused by variation in weather, to make underlying trends easier to detect. Different approaches and levels of smoothing were considered during the development of the indicator. The release presents two versions of the indicator, one with a greater degree of smoothing applied and one with a lesser degree of smoothing. A greater degree of smoothing may provide a clearer view of the underlying long-term trend, while a lesser degree of smoothing preserves the shorter-term patterns in the data. We are interested in users’ feedback on both options as part of the ongoing development of the indicator, from an Official Statistic in Development to an Official Statistic.

Future changes to the indicator

Will additional species data sets be able to be added to the 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. 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. More detail on each of these is set out in the statistics release.

There are many taxa for which sufficient abundance data is not currently available, and so are excluded from the indicator, including fungi, non-vascular plants (bryophytes and algae), microbes, amphibians and reptiles, and terrestrial invertebrates (other than moths, butterflies and bumblebees). We will review on an ongoing basis new species abundance data that may become available.

Will you engage with the Office for Environmental Protection (OEP) as part of future development of the indicator?

The Office for Environmental Protection (OEP) commissioned a review of the data and evidence that was used to develop the species abundance indicator as part of its Enironmental Improvement Plan monitoring report. In this review, the OEP acknowledge the complexities associated with developing such an indicator, and welcomed the increase in the number of species included in Schedule 2. The OEP also highlighted opportunities to strengthen the efficacy of the indicator in future. As part of the Official Statistics in Development designation we will engage with stakeholders, including the OEP, and would welcome feedback that may inform future releases.

Species specific questions

Why have some species not been included in the indicator?

The indicator has been designed with the aim of being as representative as possible of wider biodiversity in England. The indicator includes a range of species groups which, between them, depend on the majority of habitats found in England. This means that action to deliver the species abundance target will need to focus on the recovery of a broad range of habitats. Improvements to these habitats will benefit all the species that depend on them, including those not included in the indicator.

Species coverage of the indicator is limited by the availability of abundance data from existing monitoring schemes. Defined criteria were used to assess whether data were suitable for inclusion in the indicator. These ensure that abundance data come from schemes with standardised approaches, and with sufficient spatial replication across England, to provide confidence that the trends accurately reflect the national status of each species. During indicator development, we completed several reviews of the available datasets to expand the species coverage. However, we recognise that there are still taxonomic gaps in the indicator. We have set out more detail on these in the statistics release and will continue to review new data as it becomes available.

It is important to note just because a species is not included in the species abundance indicator, this does not mean that we will not be taking steps to conserve it. The indicator will be considered alongside our wider suite of biodiversity indicators, which utilise different types of species and environmental data, to assess the status of biodiversity in England. This includes the species extinction risk indicator (D5: Conservation status of our native species), which includes data for over 8,200 taxa in England (estimated to be approximately 20% of native terrestrial and freshwater species in England).

Why are there so many moths in the indicator?

Moths are well represented in the indicator because data is collected for a large number of moth species through well-established monitoring schemes. These large schemes exist because the species they monitor are considered to be useful for understanding species, habitats, and/or the wider environment. Much of the moth data comes from the Rothamsted Insect Survey, which was set up in the 1960s with the aim of studying insect population dynamics to improve understanding of the environmental impacts of pesticides.

Moths are considered to be a useful indicator species for the status of the wider environment, as they are found in many different habitats across England and are highly sensitive to environmental change. 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 changing farming practices, climate change, pesticides, and pollution. In addition:

• Moths cover a diverse range of habitats, such as grassland, heathland, woodland, and scrub habitat mosaics. These habitats are also important for a diverse range of other species that are not included in the indicator, due to insufficient data, and improvements to these habitats will benefit all of the species that depend on them.
• Moths are a key part of the food chain, providing an important food source for birds, bats, and other insectivorous species.
• Moths are important pollinators for both wild plants and crops. 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).
• A review in 2021 by Dar and Jamal provides an overview of how moths have been used as ecological indicators for different environmental pressures.

It is also worth noting that while moths represent a large proportion of the total number of species in the all-species indicator, as a proportion of all moth species in the UK, moths are not as well represented as some other species groups (including butterflies, birds, fish, and mammals). The indicator includes approximately 19% of moth species in the UK, compared with 93% of butterflies, 77% of birds, 45% of fish, and 35% of mammals.

Why are there no amphibians and reptiles in the indicator?

Amphibians and reptiles are not included in the indicator as the available abundance data for these species at the time The Environmental Targets (Biodiversity) (England) Regulations 2023 were laid was not considered to be sufficient for their inclusion in the indicator. There are seven amphibian and six reptile species in the UK, each representing approximately 0.1% of the total number of species in the UK. The small number of species in these groups means that their inclusion/exclusion from the indicator would have minimal impact on the overall trends.

However, we do recognise the importance of monitoring these species. Twelve of the thirteen amphibian and reptile species are classed as priority species, and these species are often associated with localised, unique habitats. We will continue to review abundance data for amphibians and reptiles as it becomes available, including data emerging from existing schemes supported by organisations such as Amphibian and Reptile Conservation (ARC) and the Amphibian and Reptile Group (ARG). In addition, all thirteen amphibian and reptile species in the UK are represented in indicator for the extinction risk target (D5: Conservation status of our native species).

Why are there no fungi/non-vascular plants in the indicator?

There are currently no surveillance schemes that would provide the data required to include fungi and non-vascular plants in the indicator. The available data for these species is mainly based on species occupancy rather than abundance. While these data are still useful to monitor changes in species, measures of occupancy are less sensitive to change than abundance trends and it is not possible to include them in this indicator. Our development plan for the abundance indicator includes a commitment to develop an equivalent indicator of species distribution in England, to accompany the existing priority species distribution indicator. Part of developing this new indicator will include exploring the availability of distribution data across a range of taxonomic groups, including for fungal and non-vascular plant species. This distribution indicator is in development and due to be published in the England Biodiversity Indicators in November 2025.

It is worth noting that the indicator for the species extinction risk target (D5: Conservation status of our native species) includes 47 fungal taxa and 2,357 vascular plants.

Why are there so few marine species in the indicator?

It should be noted that the species abundance target covers terrestrial/ freshwater species. With the exception of seabirds and a small number of fish living in coastal waters, the indicator does not represent marine habitats. Many marine species are highly mobile and widely dispersed and therefore assessments are done at a much larger scale (e.g. the North-East Atlantic). There are existing abundance indicators for marine species in the UK Marine Strategy and in the OSPAR assessments.