On Track of the Pale Clouded Yellow
Where it lives and how we might save it
Colias hyale in Decline
Colias hyale in Europe
The Pale Clouded Yellow can be found all over Europe from the Canary Islands to Northern Finland and from Ireland to China.
Decline in Germany
The German Butterfly Monitoring Group has recently observed a significant decline in the abundance of Colias hyale between 2005-2020 within Germany.
Decline of Colias hyale between 2005-2020
Red listed in NRW
While the signifiant decline of the Pale Clouded Yellow in Germany is evident to lepidopterologists, the species is categorized as safe on the German Red List. Meanwhile, the state of Northrhine-Westphalia (NRW) has recognized the decline and categorized the species as endangered.
So let's have a closer look at their occurrences and habitat within NRW.
Habitat
Explore the broader categories of the different land uses within a 500m radius of Colias hyale observations: pasture and open grassland, arable land, forest, open water and bogs, cities and towns, industrial usage.
ArcGIS Web Application
Pasture and Open Grassland
To get an overview of the surroundings that the adult Pale Clouded Yellow butterflies were observed in, I used the Land Use Map for Europe from 2018. The abundance of light green in their surroundings confirms that this species' most common habitat is pasture and open grassland - one of the most important habitats for European butterfly species (Rada et al. 2019).
Land Use in 500m radius of Colias hyale observations
While all light green areas are either pasture or grassland, we do not find Colias hyale just everywhere in NRW. Not all habitat is of equal value for the species' survival.
The German Conservation Union NABU (Naturschutzbund) has thoroughly examined the flora and habitat of designated biotopes that are under various measures of biodiversity protection. Only 57 out of the 639 butterfly were observed in these protected areas that are mostly designed around mammals and birds (Rada et al. 2019). But the information gathered on the habitat available within these is valuable nonetheless. Explore the map below to find out about the different kinds of open habitat that the adult Colias hyale inhabits.
ArcGIS Web Application
Threats
Butterfly populations in Germany are most threatened by habitat loss through land use changes. They benefit from clover-lucerne fields and extensive management of farm fields (Zimmermann 2017). Land use change is threatening when more land turns into urban area or is forested. My land use change analysis for NRW from 1990 to 2018 showed interesting changes in the overall area of the five most prominent land uses in a 500m radius of Colias hyale observations.
ArcGIS Web Application
While there has been an overall increase in pasture and grassland over the last 30 years, it appears as though a lot of pasture and grassland is new and in different places. Possibly suitable habitat for the Pale Clouded Yellow has thus not been consistently in the same place. Swipe the 2018 map over the map from 1990 after turning off the no change map to see for yourself. Additional grasslands are unlikely to be long established poor pastures and grasslands, prime habitat for the Pale Clouded Yellow.
Land Use Change
The data makes two hotspots visible for Colias hyale observations in NRW: Grevenbroich and Alendorf.
Here you see Alendorf, NRW. Let's look at the land use changes in this area by using the Swipe tool below: 1988 on the left, 2022 on the right.
The expansion of area with less vegetation (such as pastures) gained from arable land combined with low forestation increased the amount of habitat available for this species.
Conservation Measures
To protect the Pale Clouded Yellow, we must protect its existent habitat. Habitat loss can be limited by restricting urban sprawl. On the other hand we can try to expand the amount of habitat for Colias hyale. Below you see the proposed expansions for nature reserves and current environmentally protected areas. When you zoom in and swipe the proposed expansions, you can see a heavy focus on forest an stream protection; neither are suitable habitats for the Pale Clouded Yellow. Future reiterations of the proposed expansions should include more calciferous landscapes (poor pasture and grassland) with extensive mowing or grazing management.
ArcGIS Web Application
Besides 'pasture and grassland', 'arable land' came in as the second most common land use in a 500m radius of observed butterflies. There are different programs as part of the applications for subsidies from the European Union that can help to improve conditions for the Pale Clouded Yellow in agricultural landscapes.
Creating suitable land around farmfield parcels can provide habitat in itself and increase connectivtiy for this generalist butterfly species. The EU encourages this with programs like the 'Greening' recquirement for subsidies.
One of these programs is the 'Ackerrandstreifenprogramm' in Germany, in which farmers commit themselves to sowing a Wildflower Blend in a 5 meter perimeter of their farmland which could look like this map if everyone were to participate. This could be especially useful to expand the range further into the Northeast of NRW where there are predominantly farmfields. Zoom in or out to see the extent of this program.
Changing the management of farmfields in NRW that make up most of the state's land can have a sigificant impact on the habitat availability and connectivity for the Pale Clouded Yellow. Including more clover and various other feeding plants for the caterpillars of Colias hyale is among the top priorities for this species' protection. Less intensive mowing and grazing is the most important step in the recovery of Colias hyale.
