Butterflies Are Declining – ScienceDaily

Grassland butterflies will soon play a larger role in EU nature protection legislation. Based on the butterflies’ presence and population trends, member states are supposed to document their progress in implementing their planned “Nature Restoration Act.” The Butterfly Grass Index, recently calculated for the eighth time by the European Foundation “Butterfly Conservation Europe”, will be used for this. This analysis, which also includes data and experiences from several volunteers in Germany – coordinated by experts from the Helmholtz Center for Environmental Research (UFZ) in Halle – shows the urgency of action. This is because the status of grassland butterflies in Europe has deteriorated significantly since the first accounts in 1990.

The prognosis seems alarming: more than 80% of habitats in the European Union are currently considered to be at risk. This has negative consequences for their functional capacity and thus for the services they provide to humans. To counter this, the European Commission has proposed a new set of rules. The Nature Restoration Act is one of the key elements of the EU’s Biodiversity Strategy 2030 to be published in May. It sets binding targets for the entire European Union to rehabilitate different ecosystems. Two years after the regulation comes into force, member states must submit plans on how they intend to achieve these goals. They must also document the success of their procedures.

However, the latter is not so easy. To date, there are only a few indicators that can reliably show the state of biodiversity. For most groups of animals and plants, there is a lack of comparable data across Europe with which to assess population evolution. The few exceptions include birds, bats, and butterflies.

“Butterflies in particular are ideal bioindicators,” says agricultural ecologist Prof. Dr. Josef Settel of the UFZ. This is because these insects occur in a wide range of habitats and react sensitively to environmental changes. With their own requirements, they often represent many other insects. Finally, they are eye-catching, attractive and popular. Thus, it is relatively easy to motivate volunteers to participate in a scientifically oriented butterfly count.

Such procedures are becoming increasingly popular. For example, in 2005 the UFZ and the Gesellschaft für Schmetterlingsschutz (GfS) launched a citizen science project called “Tagfaltermonitoring Deutschland” (Butterfly Monitoring in Germany) in which anyone interested could take part. Since then, butterfly enthusiasts from all over Germany have been walking steady routes from spring to autumn to record the number of individuals and species they have seen. Similar monitoring programs now exist in most other European countries. “Now about 5,000 volunteers, spread across Europe, are participating – they all follow the same protocol,” says Settel.

Data are collected and analyzed in the central database European Butterfly Monitoring Scheme (eBMS), managed by UKCEH and reflected in the UFZ and the Dutch Vlinderstichting. In this way, the population evolution of individual species can then be tracked. Common trends can also be identified for the inhabitants of certain habitats.

That’s exactly the idea behind the Butterfly Grassland Index, which is based on population trends for 17 typical species of meadows and grasslands. If the positive and negative trends in these species are roughly balanced with each other, the indicator remains at the same level. If the number of species decreases more than it increases in the same period, the value decreases – and vice versa. Thus lower values ​​indicate greater problems among grassland populations.

Thus, the latest results of these calculations, which include data from 1990 to 2020, do not bode well. The analysis, also co-financed by the EU project SPRING (Promoting Pollinator Recovery Through Indicators and Monitoring) coordinated by the UFZ, shows only one winner: in the 27 EU member states, only the orange party (cardamom anthocharis) display a moderate increase. Three stable species: large skipper (Ochlodes sylvanus), and common copper (Lycaena phlaeas) and Meadow Brown (Manila Gortina). Five types – from the common blue (Polyomatus Icarus) to the wall brown (Lasiommata megera) – show a decrease in population. “The biggest loser in recent years has been Big Blue (Vengaris Arion), which completely disappeared in the Netherlands, for example, “For the remaining species of the 17 grassland inhabitants studied, there is either no clear trend or very little data.

The picture becomes less favorable if we look not just at the EU but at Europe as a whole. Then no species are on the rise and only three are stable. Six show a moderate decline and one a strong decline.

In light of these developments, it is not surprising that the Grassland Index is now at a much lower level than before. In the last 10 years alone, the calculated value of the European Union has fallen by 32% – and for Europe as a whole this is up to 36%. It seemed that the Grassland Population Crisis had already gripped the entire continent. This is becoming increasingly clear as more information is provided by volunteer butterfly counters from various countries. “The declines are not limited to northwest Europe,” says Chris Van Swee of Butterfly Conservation Europe. “However, the performance of some species in the south and east is much better.”

He and his colleagues attribute the dwindling occurrence of butterflies mainly to changes in agriculture. In northwestern Europe, for example, the excessive use of meadows and pastures has a particularly unfavorable effect. Extensive use of fertilizers often leads to contamination of adjacent protected areas with excessive amounts of nitrogen. In the rest of Europe, the main problem is the complete abandonment of agriculture. That’s because herbivore butterflies deal poorly with this.

According to experts, a wide range of measures is necessary to save them. It is important to promote the sustainable use of meadows and pastures, to create new valuable habitats, and to better connect existing meadows. Most grassland butterflies will also benefit from effective mitigation of climate change. “Despite all the efforts, these insects are still in decline in many parts of Europe,” says Van Sway. “We hope that the next Nature Restoration Act can stop this decline so that our children can also enjoy butterflies in the flower-rich grasslands.”