Despite frequent sightings, red squirrel habitats in Berlin are small and fragmented

Red squirrels are among the most commonly sighted wildlife in major European cities like Berlin. However, their habitats are more reminiscent of a patchwork quilt full of challenges, a team of scientists led by the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) found using computer models and squirrel sightings from Citizen Scientists. The models link sightings to numerous environmental parameters, making them important tools for urban planning as they identify areas that lack ecological corridors that could connect fragmented habitats.

The work will be published in the journal Frontiers in ecology and evolution. In a follow-up project, the team wants to close gaps in knowledge about the survival, distribution potential, nutrition and health of the Berlin red squirrel.

Squirrels – more precisely the squirrel (Sciurus vulgaris) – are also a widespread wild animal species in major European cities such as Berlin. However, the fact that they are commonly seen belies the fact that the big city is a challenging place for the rodents and suitable habitats are small and fragmented. These “islands” in the metropolitan “ocean” are often isolated, and roads and free-roaming house cats pose great challenges for the squirrels.

As a result, urban squirrels have smaller ranges than their counterparts in large, contiguous habitats. Further densification of the urban building stock could further impair the connectivity of fragmented habitats and push individual populations closer to the brink of viability. The increasing formation of heat islands in cities due to climate change could also cause additional damage. Therefore, knowledge of squirrel distribution and mortality risk in relation to built structures and other environmental variables is important for urban planning and management of urban open and green spaces.

This knowledge comes from the integration of data and their mathematical modeling at the Leibniz-IZW and the Berlin-Brandenburg Institute for Biodiversity Research (BBIB). “We were able to access data from two citizen science projects in which sightings of squirrels in Berlin were reported and the animals were registered via wildlife cameras in private gardens and allotments,” says Prof. Dr. Stephanie Kramer-Schadt, Head of the Department of Ecological Dynamics at the Leibniz -IZW and Chair of Planning-Related Animal Ecology at the Technical University of Berlin (TUB).

“These data have different levels of quality and are the result of different sample designs: The wildlife cameras were evenly distributed across Berlin in a 2×2 kilometer grid, while sightings were recorded opportunistically where and when people happened to see animals,” adds Marius Grabow, PhD student in the Kramer-Schadt department and first author of the work.

Grabow and Kramer-Schadt’s team used multiple methods to design multiple computer models that best predict squirrel appearances based on environmental variables. Environmental variables included distance to the nearest green space, distance to the nearest road, tree population and tree age, night-time temperatures, and the degree of sealing of the areas.

“Our goal was to improve spatial models in such a way that we can use existing environmental data to make predictions about the actual occurrence of the animals that are as accurate as possible – the great data from the Citizen Scientists were our reference,” says Grabow.

Using the models, the team was able to identify critical hotspots where connectivity between habitat islands is particularly important. For example on Elsenstraße/Elsenbrücke in Treptow, where the Spree and multi-lane roads separate the green areas in Treptower Park, on the Stralau Peninsula and in Schlesisches Busch/Görlitzer Park. The routes of the A111 motorway in the Tegeler Wald and Frohnau areas as well as the railway and city motorway routes between Tempelhofer Feld and the green spaces in Britz are just as “dramatic”. A positive discovery was the important long corridor for squirrels formed by a series of green spaces along the Spree. “This belt has the potential to connect the eastern and western urban areas of Berlin and is only occasionally interrupted by structural barriers,” says Grabow.

“The frequent sightings of squirrels in Berlin not only leads to the misconception that they have many good habitats in the big city, but also to the misconception that we know a lot about their lifestyle and health,” says co-author Sinah Drenske von Leibniz- IZW. “Many of the presumed findings about their movement patterns, nutrition or their state of health are actually only anecdotal,” says Drenske, who is doing her doctorate at the Leibniz-IZW and the TUB with the project “Ecology of squirrels in Berlin”. In fact, discovered Dr. Gudrun Wibbelt from the Department of Wildlife Diseases at the Leibniz-IZW, in collaboration with the consultant laboratory for smallpox viruses at the Robert Koch Institute, not long ago discovered a previously unknown strain of smallpox in Berlin squirrels, now known as the Berlin squirrelpox virus, which is deadly for young squirrels can be.

Over the next two or three years, Drenske in Berlin will repeatedly mark, measure and examine squirrels with chips and transmitters, as well as take samples and release them again immediately. Through this long-term observation, her doctoral project will provide reliable insights into the viability of the populations and their genetic structure, the state of health of the animals, their movement behavior, their diet and their ecosystem services such as seed dispersal.

“For this research, the squirrel distribution models based on the citizen science data are used to select study sites along an urban gradient in Berlin,” says Dr. Conny Landgraf from Leibniz-IZW, who works in the squirrel project. There is evidence that cities can be refuges for squirrels, e.g. B. due to the different composition of predators compared to rural areas and the complementary food intake by city dwellers.

“We still don’t know how the squirrels are doing, how many there are and how different hazards (such as roads or unsuitable supplementary food) affect the health of the squirrels,” says Drenske. “Before there is a population decline in Berlin, we want to generate relevant knowledge that can help to ensure the long-term viability of the squirrel population in the city.”

Provided by the Leibniz Institute for Zoo and Wildlife Research (IZW) in the Forschungsverbund Berlin eV