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Indicator Assessment
Although the downward trend in common bird populations is slowly leveling off, populations of all common birds in Europe — including common farmland and forest species — have declined since 1990.
Figure 1 shows that populations of common birds decreased in the 26 EU Member States that have bird populations monitoring schemes between 1990 and 2014 by around 13 %. The decrease is slightly worse (14 %) if figures for Norway and Switzerland are included. The decline in common farmland bird numbers in the same period was more pronounced, at 31.5 % (EU) and 34 % (EU plus Norway and Switzerland). While this indicator takes 1990 as a starting point, it should be borne in mind, however, that significant losses had already occurred before this date.
In spite of year-to-year fluctuations, which are typical features of butterfly populations, grassland butterfly numbers are declining significantly. Populations have decreased by around 32 % between 1990 and 2015, although in the last 10 years, there have been some signs of leveling off (Figure 2). As with bird populations, the dramatic reductions observed since 1990 are on top of population losses before that time, although no structured data series are available.
Birds and butterflies are sensitive to environmental change and their population numbers can reflect changes in ecosystems as well as in other animal and plant populations. Trends of bird and butterfly populations can, therefore, be excellent barometers of the health of the environment.
The long-term trends in common farmland, forest bird and grassland butterfly populations demonstrate that Europe has experienced a major decline in biodiversity associated with agro-ecosystems and grasslands. This has been primarily due to habitat loss, fragmentation and degradation of natural and semi-natural ecosystems. These changes have been mainly caused by homogenisation and loss of habitat as a result of agricultural intensification, intensive forest management, land abandonment and urban sprawl. For example, increased use of pesticides and herbicides results in reduced insect populations and seed production by plants, thereby reducing food for birds. Through habitat loss and fragmentation, birds lose their nesting sites, which adds to population declines. The main driver of decline in grassland butterflies is the change in rural land use. Loss of species-rich, semi-natural grasslands has been particularly detrimental.
It continues to be a challenge to achieve the wide and effective deployment of conservation measures contained in European policies such as the Birds and the Habitats Directives, and the Water Framework Directive, as well as the environmental measures within the Common Agricultural Policy (CAP) in order to help populations recover at national and European scales.
This indicator shows trends in the abundance of common birds and butterflies across their European ranges over time.
Index (relative values, 1990 set to 100)
The EU has taken action on the protection of biodiversity for a considerable number of years, for example, by adopting the Birds Directive 0409/1979 (updated in 2009/147/EC) and the Habitats Directive 0043/1992.
In line with the results of the tenth meeting of the Conference of the Parties to the Convention on Biological Diversity (CBD), held in Nagoya, Japan (October 2010), a new EU biodiversity strategy, Our life insurance, our natural capital: an EU biodiversity strategy to 2020, was adopted by the European Commission in May 2011. This provided a framework for the EU to meet its own biodiversity objectives and global commitments as a party to the CBD. The strategy is built around six mutually supportive targets, which address the main drivers of biodiversity loss and aim to reduce the key pressures on nature and ecosystem services in the EU. Each target is further translated into a set of time-bound actions and other accompanying measures. The strategy also highlights the need to enhance contributions from other environmental policies and initiatives including sectoral integration across EU policies such as agriculture, fisheries, forestry, water, climate and energy. Target 3A of the strategy seeks to maximise 'areas under agriculture across grasslands, arable land and permanent crops that are covered by biodiversity-related measures under the Common agricultural policy (CAP) so as to ensure the status of species and habitats that depend on, or are affected by agriculture'.
In 2013, the Seventh Environment Action Programme (EAP) was adopted, which will guide European environment policy until 2020.
Moreover, this indicator needs to be seen in the context of the CAP, in particular its rural development policy 2014-2020. 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.
a) Common birds
Each species reacts differently to the various anthropogenic pressures that potentially impact on population size. By monitoring a large enough number of populations from different bird groups, different bio-geographical regions and areas subjected to different types and levels of pressure, this indicator has the potential to alert decision makers to the decline in populations due to environmental and geographic factors, as well as their potential drivers.
b) Butterflies
Insects are by far the most species-rich group of animals, representing over 50 % of terrestrial biodiversity. Contrary to most other groups of insects, butterflies are well documented, easy to recognise and popular with the general public. Butterflies use the landscape at a fine scale and react quickly to changes in management, intensification or abandonment. Furthermore, a sustainable butterfly population relies on a network of breeding habitats scattered over the landscape, where species exist in a metapopulation structure. This makes butterflies especially vulnerable to habitat fragmentation. Moreover, many butterflies are highly sensitive to climate change and nitrogen deposition, and because data from fine-scale mapping are available in many countries, they have been used in models predicting the impact of climate change on wildlife. Butterflies have been counted in Butterfly Monitoring Schemes since 1976.
EU 2020 Biodiversity Headline Target
a) Common birds
The data for this indicator originates from national monitoring data collected by the Pan-European Common Bird Monitoring Scheme (PECBMS). PECBMS is a partnership involving the European Bird Census Council, the Royal Society for the Protection of Birds, BirdLife International and Statistics Netherlands that aims to deliver policy relevant biodiversity indicators for Europe
Trend information spanning different time periods is derived from annual national breeding bird surveys in 28 European countries (26 EU countries, except Croatia and Malta, plus Norway and Switzerland). Highly skilled volunteer ornithologists carry out counting and data collection. Data are collected nationally on an annual basis during the breeding season by common bird monitoring schemes. National bird monitoring data are gathered using several count methods (e.g. standardised point transects/line transects, territory mapping etc), using a variety of sampling strategies (from free choice of plots to stratified random sampling), and individual plot sizes vary within each country (from 1x1 km or 2x2 km squares or 2.5-degree grid squares to irregular polygons).
A software package named TRIM (Trends and Indices for Monitoring data) is used to calculate national species' indices and then to combine these into supranational indices for species, weighted by estimates of national population sizes. TRIM allows for missing counts in the time series and yields unbiased yearly indices and standard errors using Poisson regression. Weighting is applied to allow for the fact that different countries hold different proportions of each species' European population. Updated population size estimates, derived from BirdLife International, are used for weighting. Although count methods in the field are different in different national schemes, these differences do not influence the supranational results because the indices are standardised before being combined. An improved hierarchical imputation procedure was introduced in 2005 to calculate supranational indices. Supranational indices for species were then combined on a geometric scale to create multi-species indicators. For more details see Gregory et al. 2005.
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 2004), Cyprus (since 2006), Czech Republic (since 1981), Denmark (since 1975), 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 1994), Luxembourg (since 2009), the Netherlands (since 1984), Norway (since 1996), Poland (since 2000), Portugal (since 2004), Romania (since 2006), Slovakia (since 1994), Slovenia (since 2008), Spain (since 1996), Sweden (since 1975), Switzerland (since 1999) and the United Kingdom (since 1966).
The current population index of common birds was produced on 167 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, 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 regulus, Serinus citronella, Sitta europaea, Tringa ochropus, Turdus viscivorus.
Other common birds:
Acrocephalus arundinaceus, Acrocephalus palustris, Acrocephalus schoenobaenus, Acrocephalus scipraceus, 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, Turdus torquatus.
Rationale for species selection:
a) Birds
So far, three versions of PECBMS European species classification (farmland, forest and other) have been produced and used. The first set of European indicators was based on European trends of 47 common bird species, classified by national coordinators of monitoring schemes and other experts who met at the PECBMS workshop in Prague in 2002. For the second set of European indicators, based on an enlarged species sample, the classification was improved. It was based on a publication by Tucker & Evans (1997), describing habitats and their importance for birds in Europe. Since 2007, when the third set of European indices and indicators was produced, data on over 150 species have been used and the species classification has been based on assessments within biogeographical regions in Europe. (See the PECBMS website for further details on the historic classification.)
b) Butterflies
The field method is based on the British Butterfly Monitoring Scheme (Pollard and Yates, 1993), in use in the United Kingdom since 1976. Counts are made on a 5 m or 10 m wide line transect with homogeneous vegetation and vegetation structure. From March/April to September/October, all butterflies found 2.5 m to the left and right of the recorder and 5 m in front and above it should be counted under standardised weather conditions. The frequency varies from weekly to three or four visits during the season. Most of the sites are recorded by skilled volunteers. All recorders have a good knowledge of the butterfly fauna at their transect, and their results are checked by butterfly experts. Feest (2006), and van Swaay and Feest (forthcoming) show that butterfly survey data can be used to generate biodiversity quality indices for sites such that trends in biodiversity quality can be deduced. This will provide evidence of change more quickly than simple assessments and in a statistically robust way.
The main objective of the monitoring schemes is to assess changes in butterfly abundance at the national and regional levels, including for species included in the Habitat Directive.
A European index and trend is produced for each species by combining national results for that species. The individual European species indices are combined (averaged) to create multi-species supranational indicators. This method is based on the one for bird indicators (Gregory et al., 2005):
1. At national level, the indices for each species are produced for each country using TRIM (Pannekoek and Van Strien, 2003). TRIM is a computer programme to analyse time-series of counts with missing observations using Poisson regression.
2. At supranational level, in order to generate European trends, the difference in national population size of each species in each country has to be taken into account. This weighting allows for the fact that different countries hold different proportions of a species' European population (Van Strien et al., 2001). A weighting factor is established as the proportion of the country (or region) in the European distribution (Van Swaay and Warren, 1999). The missing year totals are estimated by TRIM in a way equivalent to imputing missing counts for particular sites within countries (Van Strien et al., 2001).
3. At multi-species level, for each year, the geometric mean of the supranational indices is calculated.
List of species
Widespread species: Ochlodes sylvanus, Anthocharis cardamines, Lycaena phlaeas, Polyommatus icarus, Lasiommata megera, Coenonympha pamphilus and Maniola jurtina.
Specialist species: Erynnis tages, Thymelicus acteon, Spialia sertorius, Cupido minimus, Phengaris arion, Phengaris nausithous, Polyommatus bellargus, Cyaniris semiargus, Polyommatus coridon and Euphydryas aurinia.
TRIM (TRends and Indices for Monitoring data) is a software package used to determine species' population trends. It allows for missing counts using estimation, and yields yearly indices and standard errors using Poisson regression. The latest version can be downloaded from the website of Statistics Netherlands.
No uncertainty has been specified
No uncertainty has been specified
MAIN DISADVANTAGES OF THE INDICATOR
a. common birds
b. butterflies
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/abundance-and-distribution-of-selected-species-6/assessment or scan the QR code.
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