Are Warsaw's urban squirrels actually more stressed by human presence?
In short: In the heart of Warsaw, red squirrels navigate a complex landscape of historic palaces and heavy human footfall. While it seems logical that urban life would spike their stress levels, recent research into these squirrels' biology suggests a much more nuanced reality regarding how wildlife adapts to our cities.
A study comparing Eurasian red squirrels in a Warsaw forest reserve and an urban park found that long-term stress levels—measured via cortisol and cortisone in hair and feces—did not differ significantly between the two populations. Interestingly, these hormone levels appeared to be influenced more by seasonality than by urban living, with concentrations notably higher during autumn and winter. Neither the sex or reproductive status of the squirrels appeared to impact these hormone levels.
While long-term physiological stress was similar, the squirrels' acute reactions to being handled showed divergence. Forest squirrels exhibited significantly higher breath rates during handling compared to their urban counterparts, suggesting they may be more sensitive to sudden disturbances. However, the struggle rate during handling was not linked to the study area, but was instead most pronounced during the winter months.
Beyond stress, the urban environment presents other biological complexities. Red squirrels in Warsaw serve as hosts for Ixodes ricinus ticks, which carry various pathogens. Molecular analysis of ticks removed from squirrels has identified Borrelia burgdorferi sensu lato, Rickettsia spp., and Babesia microti. This suggests that red squirrels may act as a reservoir for Borrelia burgdorferi and could facilitate the circulation of other tick-borne diseases in both natural and urban settings.
The coexistence of these animals within the city's largest green space—the 76-hectare Łazienki Park—highlights the intricate ways urban wildlife manages anthropogenic stressors. Understanding these mechanisms is vital, as the presence of pathogens like Babesia and Borrelia in urban squirrel populations poses a potential risk for tick-borne diseases in shared public spaces.
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Sources
- Summary by Intellect · source: Long-term, medium-term and acute stress response of urban populations of Eurasian red squirrels affected by different levels of human disturbance.
- Also: Łazienki Park
- Also: Pathogens detected in ticks (Ixodes ricinus) feeding on red squirrels (Sciurus vulgaris) from city parks in Warsaw.
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