Scientific investigations before and during the COVID-19 lockdown in Berlin in 2020 show that urban red squirrels are extremely flexible in adjusting their diurnal activities to the presence of humans, domestic dogs, domestic cats, and predators such as beech martens. With the help of wildlife cameras, scientists from the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) and citizen scientists recorded red squirrel activities in private gardens and properties over longer periods of time and compared them between the different times of day and seasons. In a paper in the scientific journal “Frontiers in Ecology and Evolution” the team describes the spatial and temporal niches occupied by the red squirrels, found that they were more active during the lockdown than before and conclude that red squirrels fear domestic cats in particular.

Eurasian red squirrels (Sciurus vulgaris) living in large cities are confronted with a multitude of challenges. At the same time, urban allotments, gardens and parks provide lots of suitable habitats for wildlife. A key survival strategy of red squirrels is to adjust their activities to the presence of humans and their pets as well as naturally occurring predators in order to make efficient use of food resources whilst minimising the risk of being harmed or killed. In particular, the constant disturbance caused by pets such as free-roaming domestic cats forces the small rodents to significantly limit their radius of action in both space and time. They avoid certain areas completely and are only active in other areas for short periods of time.

The team, led by Professor Stephanie Kramer-Schadt, head of the Leibniz-IZW Department of Ecological Dynamics and professor at the Technische Universität Berlin, analysed data from wildlife cameras from the Berlin citizen science project “wildlife researchers” (Wildtierforscher). The data were recorded in 2019 and 2020 during four surveys, including spring and autumn before and spring and autumn during the SARS-CoV-2 lockdowns. The scientific investigations focussed on the diurnal and seasonal activity patterns of red squirrels in different urban contexts and their responses to the presence of humans, domestic cats, domestic dogs and wildlife such as beech martens. “Our analyses show that red squirrels primarily change their behaviour to avoid predators and not humans”, Kramer-Schadt summarises. “They demonstrate a clear risk management behaviour and an adjustment of their temporal activity when necessary. When there were no predators in the camera trap photos, we saw an increase in their activity and the red squirrels used the time to forage on the ground. However, when predators were present, they reduced their activity to minimise the risk of becoming prey themselves.”

Free-roaming domestic cats posed the greatest threat to red squirrels, the scientists found, confirming previous studies showing negative effects of domestic cats on red squirrels and other wildlife. “In contrast, red squirrels can return to their normal behaviour when beech martens – whose presence is infrequent during the day and mainly limited to the night – are no longer active”, says Sinah Drenske, PhD student at Leibniz-IZW and first author of the paper. “However, the constant presence of domestic cats forces red squirrels to be permanently vigilant and to constantly adjust their activities.” Domestic dogs are often seen as a proxy for human activity, as people take them for walks or usually only let them into the garden when someone is at home, at least in Berlin. “Our hourly and seasonal analyses showed no significant influence of domestic dogs on the behaviour of red squirrels”, Drenske continues.

The results illustrate that the lives of red squirrels are a dynamic balancing act between food intake and minimising predation risk. “We were able to show that red squirrel activity in private gardens increased during the covid lockdowns. During this time, most people stayed at home and some took the opportunity to make their gardens more wildlife-friendly, by planting local plant species or installing bird and red squirrel feeders. The additional food sources may have encouraged red squirrels to visit gardens with feeders”, says Drenske. This observation emphasises the importance of garden design and urban planning design for the well-being of urban wildlife – with surprising positive effects: For example, the regular presence of people in urban gardens offers protection from birds of prey, which are common in the city and keep a much greater safety distance to people than red squirrels.

The work continues analyses of wildlife and pet activity based on wildlife camera traps in Berlin and research on red squirrels in the city previously published by Kramer-Schadt's team:

• A paper published in the “Journal of Animal Ecology” in 2021, for example, shed light on how red foxes, raccoons, beech martens and domestic cats interact with each other in the city and how well they get along with humans. All three wild animal species used the same localities – primarily at night and at different times. They were photographed more frequently during the lockdowns, especially at night. In addition, all wildlife species avoided the domestic cats, according to the results of the investigations at the time. With the current analysis, these findings can be extended to red squirrels. Further information in a Leibniz-IZW press release from December 23, 2021: https://www.izw-berlin.de/en/press-release/wildlife-cameras-show-how-foxes-racoons-stone-martens-and-domestic-cats-get-along-in-berlin-before-and-during-covid-lockdowns.html.
• In a paper published in autumn 2022, the scientists investigated and modelled the habitats of red squirrels in Berlin using computer models and red squirrel sightings by citizen scientists. Red squirrels are among the most frequently sighted wildlife in large cities, but the distribution of their habitats is more like a patchwork quilt. The models link the sightings to various environmental parameters and are thus an important tool for urban planning, as they identify areas where corridors connecting fragmented habitats are missing. The work was published in the scientific journal “Frontiers in Ecology and Evolution”. Further information in a press release from the Leibniz-IZW dated 20 September 2022: https://www.izw-berlin.de/en/press-release/despite-frequent-sightings-red-squirrel-habitats-in-berlin-are-small-and-fragmented.html