Abundance and distribution of selected species in Europe

Birds and butterflies are sensitive to environmental change and can indicate the health of the environment. Long-term monitoring shows significant declines in farmland birds and grassland butterflies. Between 1990 and 2019, the index of 168 common birds decreased by 8% in the 25 EU Member States with monitoring schemes. The decline in common farmland birds over the same period was much more pronounced at 27%, while the common forest bird index increased by 5%. Between 1991 and 2018 the grassland butterfly index also declined strongly, by 25%, in the 17 EU countries with monitoring data.

The status of birds and butterflies has been the subject of long-term monitoring in Europe, much of it via voluntary effort, and is a good example of how the power of citizen science can be released through effective targeting. Both species groups are sensitive to environmental change and their population numbers can reflect changes in ecosystems and other animal and plant populations. Therefore, trends in bird and butterfly populations can serve as barometers of the health of the environment and can help measure progress towards biodiversity targets.

Long-term monitoring of common birds in 25 EU Member States reveals significant population declines, particularly in farmland birds, with no signs of recovery. Between 1990 and 2019, the common bird index declined by 8%; the decline in common farmland birds was much more pronounced, at 27%; while the common forest bird index increased by 5%. Although this indicator uses 1990 as a baseline, significant decreases had occurred before this date.

The long-term trends demonstrate a major decline in biodiversity in Europe. This has been caused primarily by the loss, fragmentation and degradation of natural and semi-natural ecosystems, mainly due to agricultural intensification, intensive forest management and land abandonment or urban sprawl. Habitat loss, fragmentation and simplification (e.g. removal of hedgerows and tree lines to make fields larger) result in loss of bird nesting sites and food sources, contributing to population decline.

Factors that can have adverse effects on the recovery of populations include climate change, intensive agricultural production, urban sprawl and increasing competition for land for production of renewable energy and biofuels.

Measures set out in, for instance, the Birds and Habitats Directives, the Water Framework Directive and the common agricultural policy (CAP) aim to help populations recover at national and European levels. However, achieving the wide and effective deployment of conservation measures remains a challenge.

In spite of year-to-year fluctuations typically seen in butterfly populations, monitoring schemes in 17 EU countries reveal that, overall, grassland butterfly numbers declined significantly between 1991 and 2018, by 25%. As with the common bird index, substantial decreases occurred before the 1991 baseline for the indicator calculation.

The main driver of the decline in grassland butterfly numbers is the intensification of farming and changes in rural land use, including the abandonment of grasslands. The loss of species-rich semi-natural grasslands has been particularly detrimental. Moreover, agricultural intensification can entail high inputs of agrochemicals, including pesticides, which can dramatically reduce insect populations, including butterflies. Urban sprawl increases light pollution (i.e. artificial light at night), which is another major driver of insect decline.

Supporting information

DefinitionMethodology

Common birds

The data for this indicator originate from national monitoring data collected by the Pan-European Common Bird Monitoring Scheme (PECBMS). PECBMS is a partnership, involving the EBCC, the Royal Society for the Protection of Birds, BirdLife International and Statistics Netherlands, that aims to deliver policy-relevant biodiversity indicators for Europe. The PECBMS coordination unit is part of the Czech Society for Ornithology (CSO), based in Prague, Czechia. The unit collects national indices, produces European indices and indicators, prepares outputs for publication, and communicates outputs to the public, policymakers and scientists.

Trend information spanning different time periods is derived from annual national breeding bird surveys in 25 EU countries. Highly skilled volunteer ornithologists carry out counting and data collection. Data are collected nationally on an annual basis during the breeding season through common bird monitoring schemes. National bird monitoring data are gathered using several count methods (e.g. standardised point transects/line transects, territory mapping), using a variety of sampling strategies (from free choice of plots to stratified random sampling), and individual plot sizes vary within each country (from 1 × 1 km or 2 × 2 km squares or 2.5-degree grid squares to irregular polygons).

Indicators (multi-species indices) are computed using the MSI-tool (R-script) for calculating multi-species indicators (MSIs) and trends in MSIs. The method of calculation is described in Soldaat et al.. European, EU or regional species indices including standard errors are used as source data.

Country coverage (i.e. reflecting the availability of high-quality monitoring data from annually operated common bird monitoring schemes employing generic survey methods and producing reliable national trends): Austria (since 1998), Belgium (Brussels since 1992; Flanders since 2007; Wallonia since 1990), Bulgaria (since 2005), Cyprus (since 2006), Czechia (since 1982), Denmark (since 1976), Estonia (since 1983), Finland (since 1975), France (since 1989), Germany (since 1989), Greece (since 2007), Hungary (since 1999), Ireland (since 1998), Italy (since 2000), Latvia (since 1995), Lithuania (since 2011), Luxembourg (since 2009), the Netherlands (since 1984), Poland (since 2000), Portugal (since 2004), Romania (since 2007), Slovakia (since 2005), Slovenia (since 2008), Spain (since 1998) and Sweden (since 1975).

The current population index of common birds was produced for the following 168 species:

Common farmland birds: Alauda arvensis, Alectoris rufa, Anthus campestris, Anthus pratensis, Bubulcus ibis, Burhinus oedicnemus, Calandrella brachydactyla, Carduelis cannabina, Ciconia ciconia, Corvus frugilegus, Emberiza cirlus, Emberiza citronella, Emberiza hortulana, Emberiza malanocephala, Falco tinnunculus, Galerida cristata, Galerida theklae, Hirundo rustica, Lanius collurio, Lanius minor, Lanius senator, Limosa limosa, Melanocorypha calandra, Miliaria calandra, Motacilla flava, Oenanthe hispanica, Passer montanus, Perdix perdix, Petronia petronia, Saxicola rubetra, Saxicola torquata, Serinus serinus, Streptopelia turtur, Sturnus unicolor, Sturnus vulgaris, Sylvia communis, Tetrax tetrax, Upupa epops and Vanellus vanellus.
Common forest birds: Accipiter nisus, Anthus trivialis, Bombycilla garrulous, Bonasa bonasia, Carduelis spinus, Certhia brachydactyla, Certhia familiaris, Coccothraustes coccothraustes, Columba oenas, Cyanopica cyanus, Dendrocopos medius, Dendrocopos minor, Dryocopus martius, Emberiza rustica, Ficedula albicollis, Ficedula hypoleuca, Garrulus glandarius, Nucifraga caryocatactes, Parus ater, Parus cristatus, Parus montanus, Parus palustris, Phoenicurus phoenicurus, Phulloscopus bonelli, Phylloscopus collybita, Phylloscopus sibilatrix, Picus canus, Pyrrhula pyrrhula, Regulus ignicapilla, Regulus regulus, Serinus citrinella, Sitta europaea, Tringa ochropus and Turdus viscivorus.
Other common birds: Acrocephalus arundinaceus, Acrocephalus palustris, Acrocephalus schoenobaenus, Acrocephalus scirpaceus, Actitis hypoleucus, Aegithalos caudatus, Alcedo atthis, Anas platyrhynchos, Apus apus, Ardea cinerea, Buteo buteo, Carduelis chloris, Carduelis flammea, Cettia cetti, Circus aeruginosus, Cisticola juncidis, Clamator glandarius, Columba palumbus, Corvus corax, Corvus corone, Corvus monedula, Cuculus canorus, Cygnus olor, Delichon urbica, Dendrocopos major, Dendrocopos syriacus, Egretta garzetta, Emberiza cia, Emberiza schoeniclus, Erithacus rubecula, Fringilla coelebs, Fringilla montifringilla, Fulica atra, Gallinago gallinago, Gallinula chloropus, Grus grus, Haematopus ostralegus, Hippolais icterina, Hippolais polyglotta, Hirundo daurica, Hirundo rupestris, Jynx torquilla, Larus ridibundus, Locustella fluviatilis, Locustella naevia, Lullula arborea, Luscinia luscinia, Luscinia megarhynchos, Luscinia svecica svecica, Merops apiaster, Motacilla alba, Motacilla cinerea, Muscicapa striata, Numenius arquata, Numenius phaeopus, Oenanthe cypriaca, Oenanthe oenanthe, Oriolus oriolus, Parus caeruleus, Parus major, Passer domesticus, Phasianus colchicus, Phoenicurus ochruros, Phylloscopus trochilus, Pica pica, Picus viridis, Pluvialis apricaria, Podiceps cristatus, Prunella modularis, Pyrrhocorax pyrrhocorax, Streptopylia decaocto, Sylvia atricapilla, Sylvia borin, Sylvia cantillans, Sylvia curruca, Sylvia hortensis, Sylvia melanocephala, Sylvia melanothorax, Sylvia nisoria, Sylvia undata, Tachybaptus ruficollis, Tadorna tadorna, Tetrao tetrix, Tringa erythropus, Tringa glareola, Tringa nebularia, Tringa tetanus, Troglodytes troglodytes, Turdus iliacus, Turdus merula, Turdus philomelos, Turdus pilaris and Turdus torquatus.

More information about species indices and trends is available at: https://www.ebcc.info/pecbms/

The PECBMS European species classification (farmland, forest and other) has been developed over time as the indicators have been published and refined. The first publication was based on European trends for 47 common bird species, classified by national coordinators of monitoring schemes and other experts who met at the PECBMS workshop in Prague in 2001. For the second publication, based on an enlarged species sample, the classification was improved and was based on a publication by Tucker and Evans, describing habitats and their importance for birds in Europe. Since 2007, when the third set of European indices and indicators was published, data on over 150 species have been used and the species classification has been based on assessments within bio-geographical regions in Europe (see the PECBMS website for further details on the historic classification).

Butterflies

The data for this indicator originate from the European Butterfly Monitoring Scheme (eBMS) (a joint initiative of Butterfly Conservation Europe and the Centre for Ecology & Hydrology) and the Assessing Butterflies in Europe (ABLE) project.

The butterfly sampling method is based on butterfly transect counts. The eBMS provides methodological support to volunteers and country/regional networks, e.g. via the manual for butterfly transect counts.

The butterfly indicator is based on the fieldwork of thousands of trained professional and volunteer recorders, counting butterflies on more than 6 200 transects scattered widely across the EU under standardised conditions. National coordinators collect the data and perform the first quality control step. In 2017, more than 55 880 km of transect walks were made, more than 90 % of them by volunteers, monitoring each transect an average of 15 times per year.

For each species and year, flight periods were estimated based on climate zones as defined in Metzger et al., but with further geographical stratification to represent major geographical units (e.g. Ireland was treated as a separate unit to continental Europe). Site-level indices were produced by estimating the missing counts, and species’ collated indices were produced for each monitoring scheme using a Poisson general linear model (GLM) with site and year effects, as well as the proportion of the flight period surveyed as a weighting. A collated index for the EU was produced for each species by fitting a Poisson GLM to the scheme-level collated indices with scheme and year effects as well as a weighting. The EU indices for the 17 species were combined by taking the geometric mean of the indices using the Biological Records Centre (BRC) indicators R package. This indicator is a unified measure of biodiversity following the bird indicators as described by Gregory et al., by averaging indices of species rather than abundances to give each species an equal weight in the resulting indicators. If positive and negative changes of indices are in balance, their mean would be expected to remain stable. If more species decline than increase, the mean should go down, and vice versa. Thus, the index mean is considered a measure of biodiversity change.

For this updated indicator, data were used from 17 EU countries: Austria (since 2013), Belgium (since 1991), Czech Republic (since 2010), Estonia (since 2004), Finland (since 1999), France (since 2005), Germany (since 2005), Hungary (since 2016), Ireland (since 2007), Latvia (since 2015), Lithuania (since 2009), Luxembourg (since 2010), the Netherlands (since 1991), Romania (since 2013), Spain (since 1994), Slovenia (since 2007) and Sweden (since 2009).

The indicator is based on the following 17 species:

Widespread species: Anthocharis cardamines, Coenonympha pamphilus, Lasiommata megera, Lycaena phlaeas, Maniola jurtina, Ochlodes sylvanus and Polyommatus icarus.
Specialist species: Cupido minimus, Cyaniris semiargus, Erynnis tages,Euphydryas aurinia, Lysandra bellargus, Lysandra coridon, Phengaris arion, Phengaris nausithous, Spialia sertorius and Thymelicus acteon.

European butterfly experts selected 17 species that they considered to be characteristic of European grassland and that occurred in a large part of Europe, covered by the majority of the butterfly monitoring schemes, and with grasslands as their main habitat.

Methodology for gap filling

A Monte Carlo method is used to account for sampling error and when not all yearly index numbers for all species are available. The MSI-tool (R-script) is used to calculate Multi Species Indicators and trends in MSIs.

Methodology references

No methodology references available.

Policy/environmental relevance

Justification for indicator selection

Main advantages of the indicator:

Policy relevant: this indicator contributes to the assessment of biodiversity conservation policies and targets, as well as other sectoral and thematic policies and strategies.

Biodiversity relevant: birds and butterflies can be excellent barometers of the health of the environment. They occur in many habitats, can reflect changes in other animal and plant populations, and are sensitive to environmental change.

Scientifically sound and methodologically well founded: the methods used have been harmonised (national systems may differ but indices are standardised before being combined), and are peer-reviewed and statistically robust.

Monitors progress towards targets: this indicator provides a tangible basis for measuring progress towards biodiversity targets.

Broad acceptance and understanding: this indicator reports on birds and butterflies. Both species groups resonate strongly with the public, illustrating how citizen science can be exploited through effective targeting.

Routinely collected data.

Scientific references

No rationale references available.

Context description

The EU has been taking action to protect biodiversity for a considerable number of years, for example by adopting the Birds Directive — Council Directive 79/409/EEC (updated by Directive 2009/147/EC) and the Habitats Directive — Council Directive 92/43/EEC.

In 2011, the first EU biodiversity strategy, ‘Our life insurance, our natural capital: an EU biodiversity strategy to 2020’, was adopted by the European Commission in line with the results of the 10th meeting of the Conference of the Parties to the Convention on Biological Diversity (CBD), held in Nagoya, Japan (October 2010). This strategy provided a framework for the EU to meet its own biodiversity objectives and global commitments as a party to the CBD. It was built around six mutually supportive targets that address the main drivers of biodiversity loss and aimed to reduce the key pressures on nature and ecosystem services in the EU; however, the targets have not been reached.

The publication of the ‘EU biodiversity strategy for 2030: Bringing nature back into our lives’ in May 2020 reinforces the relevance of this indicator, in particular the commitments of the EU nature restoration plan.

This indicator also needs to be considered in the context of the CAP, in particular its rural development policy 2014-2020 and the new farm to fork strategy. Relevant policy measures under the rural development policy include agri-environment-climate schemes and payments to farmers in areas with natural constraints or for adapted farming in areas with environmental restrictions, such as Natura 2000 sites.

Targets

EU 2020 Biodiversity Headline Target

Methodology uncertainty

The indicator is accompanied by measures of uncertainty, including smoothed trends and confidence limits (at 95 % level).

Data sets uncertainty

Data on population development of a species are assessed by calculating yearly indices and standard errors using the TRIM software (Pannekoek and Van Strien, 2005, http://www.bc-europe.eu/upload/EurButtInd/trim3man.pdf)

Rationale uncertainty

Main disadvantages of the indicator

a. Common birds

Temporal coverage: until the early 1990s, rather few European countries had common bird monitoring schemes in place, which restricts how far back in time representative trends can be calculated.
No coherent and structured data breakdown at country level is currently available.

b. Butterflies

Limited geographical coverage.

Data sources and providers

Metadata

DPSIRTopicsTagsTemporal coverageGeographic coverage

TypologyUN SDGsUnit of measureFrequency of dissemination

References and footnotes

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