Comparison of multiple behavioral traits between urban and rural squirrels

Recent rapid urbanization has imposed novel challenges to animals. Urban animals alter their behaviors such as increased boldness, exploration, and aggressiveness to cope with anthropogenic disturbance. However, most previous studies were highly biased toward birds and examined a limited number of behavioral traits, often employing species-specific methods. Thus, we still do not fully understand how other taxa behaviorally adjust to urbanization. In this study, we investigated multiple behavioral traits between urban and rural Eurasian red squirrels, Sciurus vulgaris , which is one of the typical urban colonizers across northern Eurasia. The open field test (OFT) and mirror image stimulation (MIS), two well-established methods for quantifying animal personality, were employed for behavioral comparisons. We also used several other measurements, such as flight distances and the number of mobbing calls directed at humans. The principal component analysis approach for OFT and MIS provided an activity-shyness axis and stress response axis in OFT and sociability-avoidance axis in MIS, which had significant repeatability within individuals. However, most axes were not significantly different between urban and rural areas, while the stress response of urban squirrels was significantly weaker than that of rural conspecifics. On the contrary, human-related behaviors such as flight distance and the number of mobbing calls toward humans were significantly different between urban and rural habitats. Therefore, behavioral modifications reported in previous studies might reflect only human-related disturbances: some urban animals such as mammals may be able to flexibly change behaviors depending on the situation, while their innate character or personality remains unchanged. This study underscores the importance of measuring multiple behaviors using different methods in non-avian species, focusing especially on human-associated behaviors.