Over 80% decline in butterflies since late 1800s

It is the first time that the historical trend in butterfly species distribution has been established. As of 1992, data from butterfly observations have been collected systematically as part of the Dutch Butterfly Monitoring Scheme, developed by Dutch Butterfly Conservation and CBS. Over the past few decades, the distribution of butterfly species has remained stable but there has been a steady decline in population, as indicated by the latest figures published in the Environmental Data Compendium.

Decline in distribution levels off, numbers continue to decline

Distribution trends of all butterfly species found across the Netherlands have been summarised in a Multi-Species Indicator (MSI). Between 1890 and 1990, the MSI dropped by 67 percent, after which distribution stabilised. Downward trends were detected for 42 species, 15 of which have disappeared completely from the Netherlands.

As of 1992, CBS and Dutch Butterfly Conservation monitor not only the distribution of species but also their abundance. The combined trends in distribution and abundance show an estimated overall decline in butterfly populations of no less than 84 percent between 1890 and 2017. Given the fact that a population decline always exceeds a decline in distribution (a population decline from 100 to 10 still indicates the presence of a particular species), one can assume that the population decline was even more substantial.

Three years ago, CBS and Dutch Butterfly Conservation still reported that slightly more butterfly populations had increased rather than decreased for the first time since population monitoring started in the early 1990s. Populations of some rare species such as the dark green fritillary, the tree grayling and the small pearl-bordered fritillary in particular showed a modest increase again following specific conservation efforts. However, the latest figures - published in the Environmental Data Compendium - show a continued downward trend, also among the rare species. Out of the 50 species monitored, 25 declined while 14 increased in number over the entire period, with 31 species declining and 9 species increasing over the past decade.

Trend stabilises in grassland and woodland, decline continues in heathland

Predominantly until 1980, butterfly abundance dropped sharply in all three major butterfly habitat types in the Netherlands: grassland, woodland and heathland. The trend has stabilised since then in grassland and woodland, but the decline has continued in heathland.

One century ago, almost all grasslands in the Netherlands were rich in herb species Since then, farming practices have intensified, eliminating grassland herb species (almost) entirely. The species richness as it once existed can nowadays only be found in nature reserves. Due to nature restoration, the area of semi-natural grassland has expanded somewhat in recent years, which locally have also resulted in a higher abundance of rare species.

Improved conditions for woodland species

The recent expansion of several rare woodland butterflies (wood whites, white admirals, purple emperors and silver-washed fritillaries) indicates that habitat conditions are improving, possibly favoured by climatic warming in combination with a modest revival of small-scale woodland management practices. Woodland cover has expanded over the 20th century and the proportion of mature woodland increased. This has led to diversification in woodland structure and composition.

Sustained decline in heathland species

Until 2000, heathland butterfly species decreased less strongly in occurrence than grassland and woodland species. At sites where heathland persisted after major extractions, the population of typical heathland butterflies remained stable for a long time. However, their number has been declining in all areas lately. This is due to the combined effects of fragmentation of the remaining heathland area and soil acidification and eutrophication due to atmospheric nitrogen deposition.

Decline also seen in other European countries

Strong declines in butterflies have been reported from other European countries (e.g. Belgium, Finland and the United Kingdom) as well, although few studies look back as far as this research does. On a comparable time-scale (1840–2013), severe declines (46 out of 117 species lost) were also recorded in south-eastern Bavaria. A decline in species richness similar to that in the Netherlands is reported in Belgium and the United Kingdom for the period 1950-2009. On a continental scale, the European Red List of Butterflies shows many more declining species (31 percent) than increasing species (4 percent) for 1998-2008. Around 9 percent of the European species are currently considered endangered.

The Dutch Butterfly Monitoring Scheme is a joint scheme of Dutch Butterfly Conservation and Statistics Netherlands and is financed by the Ministry of Agriculture, Nature and Food Quality in the framework of the Dutch Network Ecological Monitoring programme.