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.

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Figure 1. Common Birds in Europe — population index, 1990-2019
YearAll common birds (168 species)Common farmland birds (39 species)Common forest birds (34 species)
1990100100100
1991100.1698.71100.49
1992100.2697.46100.74
1993100.3996.41100.82
1994100.4895.41100.78
1995100.4994.36100.64
1996100.3693.11100.45
199799.9891.5999.97
199899.4189.8799.07
199999.3488.0697.96
200097.7286.2596.83
200196.9584.5795.88
200296.3483.0995.28
200395.8381.7394.93
200495.3280.4294.66
200594.8479.1894.48
200694.4178.494.42
200794.0677.0694.52
200893.876.294.75
200993.5775.4195.11
201093.3874.7195.58
201193.2474.0996.17
201293.1573.5696.87
201393.0973.1197.7
201493.0872.7598.65
201593.1372.4899.74
201693.2172.27100.95
201793.3372.14102.32
201893.4572.01103.71
201993.5771.88105.12

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.

Figure 2. Grassland butterflies — population index, 1991-2018
YearGrassland butterflies (17 species)Trend linelower confidence limit of the smoothed indicatorupper confidence limit of the smoothed indicatorConfidence limits
1990
1991109.6110072.320277151.4027579.082473
1992100.1998.0173.074929145.3832772.308341
199386.1196.3171.891266139.653267.761934
199486.9894.9871.38882134.5536463.16482
1995107.0494.1670.497374131.5270661.029686
199688.293.6970.030061129.0841459.054079
199785.4393.2670.064413125.7380355.673617
199876.2493.3670.551859123.9318953.380031
199978.9894.271.431413123.3932351.961817
2000107.495.0772.264019122.9559850.691961
200184.595.2572.942177122.261549.319323
2002134.2494.4373.64103120.5602146.91918
200398.1893.1374.114976119.1025844.987604
200484.6391.8673.940127117.2341643.294033
200577.1389.9873.287199114.2727640.985561
200679.4387.1672.491151109.4506836.959529
200782.7984.3170.286059104.3310634.045001
200872.3582.3369.245079101.2802232.035141
200990.181.6368.79210899.20508730.412979
201086.0981.4668.51368997.54895529.035266
201191.9480.9468.4255195.89193627.466426
201278.3880.0968.51366193.72750325.213842
20138479.468.63116291.73123323.100071
201489.3178.7268.48437289.63046821.146096
201565.0977.9168.61431987.58292618.968607
201673.2176.9268.98290485.3003916.317486
201781.4575.8268.89004383.06714914.177106
201872.3274.6768.37407881.90928313.535205

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.

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