Accredited official statistics

7 - Wetland species

Updated 7 May 2024

Applies to England

© Crown copyright 2024

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This publication is available at https://www.gov.uk/government/statistics/england-biodiversity-indicators/7-wetland-species

Data last updated: November 2023

Latest data available:

  • Breeding wetland birds (National Statistics) - 2022
  • Wintering waterbirds (National Statistics) - 2021/2022
  • Abundance of wetland plant species (Official Statistics in Development) - 2022

Introduction

This indicator shows changes in relative abundance of breeding wetland bird species, wintering waterbird species, and plant species considered indicative of good habitat condition on bog and wet heath in the UK.

Wetlands, including rivers, lakes, ponds, reedbeds, grazing marshes and lowland raised bogs provide important habitats for breeding wetland birds. The term waterbirds refers to species of birds that depend on water or its adjacent habitats. Some species of waterbirds that overwinter along England’s coasts and on inland water bodies also breed in England, but many only come to England for the winter. Plant populations form the environment in which most other species exist, as well as providing numerous ecosystem services.

Type of indicator

State indicator

Assessment of Change

Assessment of change in species in the wider countryside: wetlands

  • Breeding wetland birds (National Statistics):
    • Long term (1975 to 2021): Little or no overall change
    • Short term (2016 to 2021): Deteriorating
    • Latest year (2022): Decreased
  • Wintering waterbirds (National Statistics):
    • Long term (1975/76 to 2020/21): Improving
    • Short term (2015/16 to 2020/21): Deteriorating
    • Latest year (2021/22): No available data
  • Abundance of wetland plant species (Official Statistics in Development)
    • not assessed

Note on the assessment:

To better capture underlying trends, long and short-term assessments are made on the basis of smoothed data. Due to the smoothing method, the most recent smoothed data point is likely to change when a subsequent year of data is added. Long and short-term assessments using smoothed data are therefore made to the penultimate year’s datapoint, whereas all latest year assessments are based on unsmoothed data.

The significance of change in the breeding wetland bird indicator is tested by bootstrapping, a formal statistical approach. This is not appropriate for assessing the wintering waterbird indicator. On the advice of the data providers, changes are assessed using a rule of thumb whereby a change of 5% or more is deemed significant.

Due to the impacts of COVID-19, there are no unsmoothed data available for wintering waterbirds in 2020/21, as such a latest year change assessment is unavailable.

Breeding wetland birds (National Statistics)

Trend description for Figure 7.1

Produced largely using the population trends from surveys in or alongside wetland habitats, the water and wetland bird index has remained fairly stable for most of the period since data collection started in 1975. In 2022 the water and wetland bird index was 3% lower than in 1975. In the short term the index decreased by 8%.

Since 1970, of the 25 species for which a long-term trend can be calculated, 24% of species increased, 48% showed little change and 28% declined, with more species exhibiting a weak rather than a strong change. For little egret, data can only be included from 2004 and therefore a long-term trend could not be calculated (for more information on the time series used for different species long-term trends, (see datasets provided alongside this publication).

Figure 7.1: Trends for the abundance of breeding wetland birds in England, 1975 to 2022

Download the data for Figure 7.1 in ods format

Figure 7.2: Long-term and short-term changes in individual species trends for breeding wetland birds in England, 1970 to 2021

Download the data for Figure 7.2 in ods format

Notes about Figures 7.1 and 7.2

  • this indicator includes individual measures for 26 species of water and wetland birds
  • Figure 7.1 shows the unsmoothed trend (dashed line) and the smoothed trend (solid line) together with its 95% confidence interval (shaded)
  • Figure 7.2 shows the percentage of species within the indicator that have increased, decreased or shown little change, based on set thresholds of annual change
  • Figure 7.2 is presented as a stacked bar chart and the legend is presented in the same order as the stacks in the bar chart
  • Figure 7.1 shows the lower confidence intervals for 1994 and 1995 were un-estimable, this is due to the high uncertainty around the population trend for Snipe which is a scarce species. As a result the lower confidence intervals on the graph abridges the two data points for 1993 and 1996

Source: British Trust for Ornithology, Defra, Joint Nature Conservation Committee and the Royal Society for the Protections of Birds

Wintering waterbirds (National Statistics)

Trend description for Figure 7.3

In the winter of 2021/2022, the wintering waterbird index was 88% higher than in the winter of 1975/1976. The index peaked in the late 1990s, and has declined since, with the index falling by 8% between the winters of 2016/2017 and 2021/2022.

Since 1975/1976, 44% of wintering waterbird species increased, 41% showed little change and 15% declined, most of these showing a weak decline.

Figure 7.3: Trends for the abundance of wintering waterbirds in England, 1975/76 to 2021/22

Download the data for Figure 7.3 in ods format

Figure 7.4: Long-term and short-term changes in individual species trends for wintering waterbirds in England, 1975/76 to 2020/21

Download the data for Figure 7.4 in ods format

Notes about Figures 7.3 and 7.4

  • this indicator includes individual measures for 41 species of wintering waterbird of which 22 are wildfowl species and 15 are wader species
  • Figure 7.3 shows the unsmoothed trend (dashed line) and smoothed trend (solid line). Data from wintering waterbirds monitoring schemes are based largely on full counts at colonies or at wetland and coastal sites of markedly varying size. This means that bootstrapping methods cannot be applied reliably and hence trends for these groups are currently presented without confidence intervals
  • the number of species in each sub indicator do not sum to the number in the all-species indicator because 4 species are included in all wintering waterbirds but are neither wildfowl nor wader. These are 2 grebes (little and great-crested), one rail species (coot) and cormorant. These are in 3 different taxonomic groups, none large enough to warrant a separate indicator
  • Figure 7.4 shows the percentage of species within the indicator that have shown a statistically significant increase (strong or weak increase), a statistically significant decrease (strong or weak decline) or no statistically significant change (little change or no change) over the long-term and short-term assessment periods
  • Figure 7.4 is presented as a stacked bar chart and the legend is presented in the same order as the stacks in the bar chart

Source: British Trust for Ornithology, Defra, Joint Nature Conservation Committee and the Royal Society for the Protections of Birds

Composite indicators can mask a lot of variation among the species within them. The bar charts provided alongside the headline charts (Figures 7.2 and 7.4), shows the percentage of species within the indicator that have increased, decreased or shown little change. Whether an individual bird species is defined as increasing or decreasing has been decided by its rate of annual change over the time period (long or short) of interest.

If the rate of annual change would lead to a population decrease of 50% (halving), or a population increase of 100% (doubling) or more over 25 years, the species is said to have shown a ‘strong decline’ or a ‘strong increase’ respectively. Rates of change less than these but above an increase of 33% or below a decrease of 25% are labelled ‘weak’. Asymmetric thresholds are used for declines and increases to represent an equivalent symmetrical proportional change in an index. These thresholds for decline are based on the rates used in the Birds of Conservation Concern status assessment for birds in the UK.

Note that for most species, particularly over the longer period, the change is statistically significant.

Abundance of wetland plant species (Official Statistics in Development)

The Biodiversity Indicators project team would welcome feedback on the novel methods used in the development of this indicator.

Data collection for the National Plant Monitoring Scheme was severely affected by the COVID-19 pandemic. Due to this, the species abundance estimates for 2020 are likely to be biased and should be treated with caution.

This indicator measures, in small plots, change in the abundance of plant species considered indicative of good habitat condition on bog and wet heath in the UK, using modelled abundance data from the National Plant Monitoring Scheme (NPMS). Plant populations form the environment in which most other species exist, as well as providing numerous ecosystem services

Trend description for Figure 7.5

Between 2015 and 2022, average indicator plant abundance for the bog and wet heath habitat type included within this UK indicator shows a 11% decline since 2015 (Figure 7.5).

Figure 7.5: Trends for the abundance of plant species in one broad UK wetlands habitat, 2015 to 2022

Download the data for Figure 7.5 in ods format

Notes about Figures 7.5

  • figure 7.5 shows the unsmoothed trends (dashed lines); the variation around the lines shown (the shaded areas) is the standard deviation of 1,000 simulated trend indices calculated according to the method of Soldaat, L.L., Pannekoek J., Verweij, R.J.T., Van Turnhout, C.A.M. and Van Strien, A.J. (2017). A Monte Carlo method to account for sampling error in multi-species indicators. Ecological Indicators, 81: 340–347 doi:10.1016/j.ecolind.2017.05.033
  • abundance is measured by the percentage area covered by a species within a plot
  • the figures in brackets indicate the number of species or species aggregates included in the composite index for that particular habitat type
  • data collection for the National Plant Monitoring Scheme was severely affected by the COVID-19 pandemic, and the species abundance estimates for 2020 are likely to be biased and thus should be treated with caution

Source: Botanical Society of Britain and Ireland, Joint Nature Conservation Committee, National Plant Monitoring Scheme, Plantlife and the UK Centre for Ecology & Hydrology

The National Plant Monitoring Scheme (NPMS) was designed to monitor UK habitats of conservation importance. This is achieved through the establishment of small plots in areas of habitats targeted by the scheme. The abundances of plant species, measured as the percentage area covered by a species within a plot, are recorded each year. Surveyors record from different lists of indicator species depending on their level of experience and the habitat within which a plot is located. Both the placement of plots, and the selection of 1 kilometre national grid squares within which the plots are located, are subject to statistical methodologies designed to minimise bias (Pescott et al., 2019a).

The design of the NPMS included the definition of a set of 11 broad habitat types, within which 28 finer habitat types are nested. These fine-scale habitats are linked to existing classifications such as the British National Vegetation Classification. Surveyors can choose, based on their knowledge of a habitat, whether to record a plot at the broader or finer level. The current indicator summarises species’ percentage cover (abundance) data at the broad habitat level. This is done using a model that is able to account for both the range of percentage covers that a species may exhibit in a habitat when present, and the fact that species may often be absent from any given plot (Pescott et al., 2019b). Such data are often described as ‘zero-inflated’. This model is applied across years for each species and habitat combination, and the indicators presented here for each broad habitat are the result of combining the resulting species and habitat time trends across the relevant set of NPMS habitat indicator species.

The broad wetland habitat measure presented in this indicator is a subset of those for which the largest numbers of NPMS plots currently exist. See the technical background document for more detail.

Further information

Relevance

Bird populations have long been considered to provide a good indication of the broad state of wildlife. Birds occupy a wide range of habitats and there are considerable long-term data on changes in bird populations, which help in the interpretation of shorter-term fluctuations in numbers. As they are a well-studied taxonomic group, drivers of change for birds are better understood than for other species groups, which allows for better interpretation of any observed changes. Birds also have huge cultural importance and are highly valued as a part of England’s natural environment by the general public.

Plants are a large part of the fundamental fabric of which habitats are made and directly indicate changes to environmental conditions and habitat management. Plants provide essential habitats and food for wildlife, and essential ecosystem services for humans, such as reduced erosion, nutrient cycling, oxygen production, and climate regulation.

The indicator shows progress with commitments to improve the status of our wildlife and habitats. It is relevant to outcomes 1 and 3 in Biodiversity 2020: A strategy for England’s wildlife and ecosystem services (see Annex A).The indicator is also relevant to international goals and targets (see Annex B of the aforementioned publication).

The UK and England Biodiversity Indicators are currently being assessed alongside the Environment Improvement Plan Targets, and the new Kunming-Montreal Global Biodiversity Framework Targets, when this work has been completed the references to Biodiversity 2020 and the Aichi Global Biodiversity Framework Targets will be updated.

Background

Breeding wetland birds

The breeding wetland bird indicator has been supplied by the British Trust for Ornithology (BTO), the Royal Society for the Protection of Birds (RSPB) and the Joint Nature Conservation Committee (JNCC) with previous support for the Waterways Breeding Bird Survey (WBBS) from the Environment Agency. It is compiled using data from the WBBS and its predecessor the Waterways Bird Survey (WBS), the Breeding Bird Survey (BBS) and its predecessor the Common Bird Census (CBC), the Heronries Survey and the Constant Effort Site scheme (CES). Within the breeding wetland bird measure there are 26 species (Table 7.1). Each species is given equal weighting and the index is the geometric mean of the individual species indices. Bird count data from 300 to over 3,000 sites (depending on the data source for the species) surveyed annually by volunteers are analysed using log linear models to calculate population trends for each species. The longer-term changes in the indicator are assessed using the version of the indicator generated from the smoothed species trends, with bootstrapping used to generate confidence limits.

Although the breeding wetland bird measure shows little change since 1975, this apparent stability masks variation within the indicator, particularly between species of different water and wetland habitats. In particular, birds of wet grassland have shown substantial declines, with widespread declines in breeding waders and the yellow wagtail having declined by 95% in riverine habitats, whilst birds of slow and standing water, such as mallard, have on average increased (see Figure 7.6).

Table 7.1: Bird species included in the breeding wetland bird indicator

Common.name Species Habitat
Common sandpiper Actitis hypoleucos Fast flow
Dipper Cinclus cinclus Fast flow
Goosander Mergus merganser Fast flow
Grey wagtail Motacilla cinerea Fast flow
Coot Fulica atra Slow flow/stand
Great-crested grebe Podiceps cristatus Slow flow/stand
Little grebe Tachybaptus ruficollis Slow flow/stand
Mallard Anas platyrhynchos Slow flow/stand
Moorhen Gallinula chloropus Slow flow/stand
Tufted duck Aythya fuligula Slow flow/stand
Curlew Numenius arquata Wet grassland
Lapwing Vanellus vanellus Wet grassland
Little egret Egretta garzetta Wet grassland
Mute swan Cygnus olor Wet grassland
Redshank Tringa totanus Wet grassland
Snipe Gallinago gallinago Wet grassland
Teal Anas crecca Wet grassland
Yellow wagtail Motacilla flava Wet grassland
Cetti’s warbler Cettia cetti Reedbeds
Reed bunting Emberiza schoeniclus Reedbeds
Reed warbler Acrocephalus scirpaceus Reedbeds
Sedge warbler Acrocephalus schoenobaenus Reedbeds
Grey heron Ardea cinerea Other
Kingfisher Alcedo atthis Other
Oystercatcher Haematopus ostralegus Other
Sand martin Riparia riparia Other

Figure 7.6: Breeding wetland birds across 4 wetland habitats in England, 1975 to 2022

Download the data for Figure 7.6 in ods format

Notes about Figure 7.6:

  • the line graphs show unsmoothed trends (dashed lines) and smoothed trends (solid lines)
  • the figures in brackets show the number of species in each measure
  • Source: British Trust for Ornithology, Defra, Joint Nature Conservation Committee, Royal Society for the Protection of Birds.

Wintering waterbirds

The wintering waterbird indicator has been supplied by the British Trust for Ornithology (BTO), the Royal Society for the Protection of Birds (RSPB) and the Joint Nature Conservation Committee (JNCC) with support from the Wildfowl and Wetlands Trust (WWT). It is compiled using data from the Wetland Bird Survey (WeBS) and WWT Goose and Swan Monitoring. There are 41 species, races and populations of bird included in the wintering waterbird indicator. These can be split into subcategories of wildfowl (ducks, geese and swans) and waders (sandpipers, plovers and their close relatives) which display slightly different trends. Overall, the wildfowl index has increased considerably by 91% and the wader index has increased by 71% between 1975/1976 and 2021/2022. However, both show parallel changes, having peaked in the late 1990s have declined subsequently between 2016/2017 and 2021/2022, both the indices for wildfowl declined by 11% and waders declined by 4%.

Since 1975/1976, 50% of the wildfowl species increased, 32% showed little change and 18% declined. Notable strong increases included the British/Irish greylag goose, whooper swan, gadwall and the Svalbard light-bellied Brent goose; wintering numbers of which increased by at least 41-fold, 25-fold, 15-fold and 11-fold respectively in the long term. Numbers of wintering Bewick’s swan and scaup have declined most strongly by 87% and 77% respectively since 1975/1976. There were also long-term declines for: European white-fronted goose by 70% and pochard by 50%.

Since 1975/1976, 33% of the wader species increased, 53% showed little change and 13% declined. Wintering numbers of avocet and black-tailed godwit increased by over 12-fold and 8-fold respectively in the long term. In contrast, numbers of ringed plover decreased by 53% and dunlin by 49% since 1975/1976.

Wintering wetland birds are affected by a range of factors including conditions in the high latitude countries where they breed, with breeding productivity increasing for species including black-tailed godwit but decreasing for others such as Greenland white-fronted geese. There is good evidence of a strong climate change impact on the indicator in recent years, with the pattern of milder winters leading to the wintering ranges of many species, including mallard, pintail, goldeneye, pochard, bewick’s swan, ringed plover and bar-tailed godwit, increasingly shifting north and east and away from the UK as more birds are able remain in areas closer to their northern breeding grounds. In addition, local changes, such as wetland creation and changes in agricultural management, have had an impact on wintering waterbird populations within the UK.

Table 7.2: Bird species included in the wintering waterbird indicator

Common.name Species Habitat
Bewick’s swan Cygnus columbianus Wildfowl
British/Irish greylag goose Anser anser anser Wildfowl
Dark-bellied brent goose Branta bernicla bernicla Wildfowl
Eider Somateria mollissima Wildfowl
European white-fronted goose Anser albifrons albifrons Wildfowl
Gadwall Anas strepera Wildfowl
Goldeneye Bucephala clangula Wildfowl
Goosander Mergus merganser Wildfowl
Mallard Anas platyrhynchos Wildfowl
Mute swan Cygnus olor Wildfowl
Pink-footed goose Anser brachyrhynchus Wildfowl
Pintail Anas acuta Wildfowl
Pochard Aythya ferina Wildfowl
Red-breasted merganser Mergus serrator Wildfowl
Scaup Aythya marila Wildfowl
Shelduck Tadorna tadorna Wildfowl
Shoveler Anas clypeata Wildfowl
Svalbard light-bellied brent goose Branta bernicla hrota Wildfowl
Teal Anas crecca Wildfowl
Tufted duck Aythya fuligula Wildfowl
Whooper swan Cygnus cygnus Wildfowl
Wigeon Anas penelope Wildfowl
Avocet Recurvirostra avosetta Wader
Bar-tailed godwit Limosa lapponica Wader
Black-tailed godwit Limosa limosa Wader
Curlew Numenius arquata Wader
Dunlin Calidris alpina Wader
Golden plover Pluvialis apricaria Wader
Grey plover Pluvialis squatarola Wader
Knot Calidris canutus Wader
Lapwing Vanellus vanellus Wader
Oystercatcher Haematopus ostralegus Wader
Purple sandpiper Calidris maritima Wader
Redshank Tringa totanus Wader
Ringed plover Charadrius hiaticula Wader
Sanderling Calidris alba Wader
Turnstone Arenaria interpres Wader
Coot Fulica atra Other
Cormorant Phalacrocorax carbo Other
Great crested grebe Podiceps cristatus Other
Little grebe Tachybaptus ruficollis Other

Wetland plants

The creation of the NPMS allowed for the creation of annual trends in the abundance of plants in habitats of conservation importance. Following 5 years of development, the scheme was launched by a partnership consisting of the Botanical Society of Britain and Ireland (BSBI), the Joint Nature Conservation Committee (JNCC), Plantlife, and the UK Centre for Ecology & Hydrology (UKCEH) in 2015. This indicator uses a subset of the species selected by the NPMS as indicative of good condition in those habitat types considered to be of most importance for the conservation of UK biodiversity – see the technical background document for a full list of species included. These species are monitored in small sample plots (between 25 and 100 square metres in area) according to a methodology that was designed to minimise biases in data collection. Results for the UK bog and wet heath habitats are presented here in the wetland plant species abundance indicator.

Since 2018, UKCEH, with input from all partners, have been developing a method of using NPMS data to indicate annual changes in habitat condition. The method is based on a hierarchical model, formulated in a Bayesian framework, that integrates information on a species’ abundance and occupancy; the occupancy estimates also take advantage of the fact that most plots are surveyed twice a year, allowing adjustments for false negatives (that is, species that are overlooked during surveys). Simulation tests and applications to real data indicate that the method is robust and produces ecologically sensible metrics.

The 1 kilometre squares of the NPMS were selected according to a weighted-random algorithm designed to introduce a known bias towards semi-natural habitats. However, within this design, a sampling bias exists in that, in common with other UK structured monitoring schemes based on volunteer participation, squares located within lowland areas are more likely to be sampled. Further work will focus on additional adjustment for bias (Pescott et al., 2019b).

References

  • Pescott, O.L., Walker, K.J., Harris, F., New, H., Cheffings, C.M., Newton, N., Jitlal, M., Redhead, J., Smart, S.M. and Roy, D.B. (2019a). The design, launch and assessment of a new volunteer-based plant monitoring scheme for the United Kingdom. PLoS ONE, 14(4): e0215891.
  • Pescott, O.L, Powney, G.P. and Walker, K.J. (2019b). Developing a Bayesian species occupancy/abundance indicator for the UK National Plant Monitoring Scheme. Wallingford, NERC/Centre for Ecology & Hydrology and BSBI, 29pp. DOI:10.13140/RG.2.2.23795.48161
  • Soldaat, L.L., Pannekoek J., Verweij, R.J.T., Van Turnhout, C.A.M. and Van Strien, A.J. (2017). A Monte Carlo method to account for sampling error in multi-species indicators. Ecological Indicators, 81: 340–347 DOI:10.1016/j.ecolind.2017.05.033
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