Research Award 2025

From ponds to pondscapes: habitat characteristics influencing the abundance of the threatened yellow-bellied toad (Bombina variegata)

Cyann Winkler examined over 500 pools spread across 33 locations in four landscapes in western Switzerland. The focus was on the yellow-bellied toad, an amphibian species that is classified as endangered in Switzerland according to the Red List. Which characteristics of the pools and their surroundings are decisive in determining whether or not the toad is present? For each body of water, three night-time inspections were carried out to determine whether toads were present and, if so, in what numbers. Various characteristics of the habitat were also recorded. These included, for example, the number of ponds in the area, the material of the pond substrate, the type and number of potential hiding places near the shore, and the extent of sunny or shady areas. 

Statistical analysis of the extensive data revealed that the more ponds there are in close proximity to each other at a given location, the more likely it is that the toad will be found there and the larger its local population will be. Based on this statistical correlation, the award winner recommends a minimum of eight ponds per location in order to establish a local toad population. Ideally, there should be up to 20 ponds next to each other. New pools should be created within a maximum radius of 150 m from existing pools. The award winner found that pools are reliably colonised within this distance, provided that there are no obstacles such as roads, walls or rivers preventing access. The quality of the individual pools is also important: pools in sunny locations, preferably with a sandy-gravelly or loamy substrate and with hiding places made of stone or wood directly adjacent to the banks, have proven to be particularly suitable. However, the clear focus is on the realisation that large and stable populations of yellow-bellied toads require entire ‘pond landscapes’ with a large number of high-quality water sources. The very specific and broadly supported recommendations make Cyann Winkler's study particularly valuable and helpful. It thus gives new impetus to the promotion of a target species that is so important for nature conservation.

What’s left of it. Multifactorial Restructuring of impoverished, urban Butterfly Communities

Almost 50 per cent of butterfly species have disappeared from the urban landscape in and around the city of Bonn within 80 years. This alarming finding comes from Maximilian Schiefer's excellent study. It is based in part on historical butterfly data from three periods between 1943 and 2024. The most severe losses occurred between approximately 1940 and the mid-1990s. Butterfly species with limited flying ability were particularly affected, as were species that are highly specialised to certain habitats or individual plant species. Butterflies are heavily dependent on the availability of food plants for their caterpillars. In searching for the reasons for this dramatic decline, it was therefore obvious to consider changes in vegetation.

To this end, the award winner used 30-year-old data on the botanical species composition of four protected areas and compared it with his own repeated measurements. He was thus able to show that the four areas had retained their botanical quality over decades, while at the same time the butterfly community had become profoundly impoverished. Maximilian Schiefer concludes from all his findings that, in addition to the loss of certain habitat types and climate change, it was above all the reduced connectivity of the remaining butterfly habitats that led to the decline in butterfly species in the Bonn area. The isolated habitat islands were not sufficient to maintain viable populations of many butterfly species. He concludes that the importance of small and isolated nature reserves for the protection of butterflies needs to be reassessed. His study, which is exemplary for the Bonn area, emphasises the urgency of connecting existing habitats. Additional areas of suitable quality are needed within reach of the isolated species populations. Otherwise, the negative trends observed are likely to continue.