Fewer hedgehogs in the city: a small pedestrian under pressure
The hedgehog population in Zurich has declined by 40% over 25 years. Habitable area has shrunk by 18%. Soil sealing and light pollution are threatening the species.
Hedgehogs today live at higher densities in urban areas than in rural regions. Yet even here, hedgehogs are coming under increasing pressure. A new study from the city of Zurich shows that the hedgehog population has declined by 40% over the past 25 years, and that the area inhabited by hedgehogs has shrunk by 18%.
The hedgehog's habitat has changed dramatically over the past 50 years. With the intensification of agriculture, rural areas became more monotonous and structurally impoverished. As a result, hedgehogs were increasingly found in urban settings, where they discovered new habitats in leafy residential neighbourhoods. A StadtWildTiere study conducted by the research group SWILD as part of the project and recently published in the journal Animals study shows for the first time that hedgehogs are now also coming under pressure in urban residential areas and that their numbers are in decline.
The study is based on data from two citizen science projects: a current project from the StadtWildTiere observation reporting platform covering the years 2016 to 2018, and a research project from 1992. At that time, the population of Zurich was invited via report cards to submit hedgehog sightings. In addition, hedgehogs were studied using telemetry in two survey areas, and a population estimate was made based on hedgehog counts. These data were compared with the new research conducted as part of the StadtWildTiere citizen science project, which collects hedgehog sightings from city residents on the reporting platform stadtwildtiere.ch.
In 2016, the distribution of hedgehogs in the city of Zurich was additionally recorded systematically using tracking tunnels, with the help of the local population. Tracking tunnels are a common wildlife biology method in which laminated cardboard tunnels, equipped with ink pads and paper strips, are placed in hedgehog habitats. When a hedgehog walks through a tracking tunnel, it leaves its footprints on the paper. The tracks thus provide information about the occurrence of this small wild animal. In addition, in 2017 the population size was recorded using the capture-recapture method. Significant decline in the hedgehog population — causes still unclear
A comparison of data from the two citizen science projects shows that hedgehog populations have declined sharply over the past 25 years: the population size in the city of Zurich has decreased by 40% (from around 1,500 to fewer than 900 hedgehogs) and the urban area inhabited by hedgehogs has shrunk by 18%.
The reasons for this marked decline are currently still largely unclear. Various factors could be contributing to the decline, including the increasing densification of urban habitats, a decrease in biodiversity in gardens, growing habitat fragmentation due to roads, walls and fences, the use of pesticides, an increase in the badger population, rising road traffic, as well as parasites or disease.
The results are concerning, as they suggest that hedgehogs are coming under increasing pressure not only in rural areas, but also in cities, where green residential areas were previously considered refuges for the hedgehog as a species adapted to human environments. The research group is planning further investigations to clarify the causes of the decline.
