Comparison of multiple behavioral traits between urban and rural squirrels

Abstract

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.

Of city and village mice: behavioural adjustments of striped field mice to urban environments

“…Reported results of increasing boldness with increasing urbanisation are consistent with the results of previous studies, which suggested that a higher risktaking tendency is adaptive during invasion of novel environments (e.g. 65,81 , but see 82 ). Higher boldness, defined as an individual's reaction to any risky situation, including encounters with predators and humans 17 is thus likely to help coping with the threats and challenges posed by "city life", from traffic and other human disturbances to responses to higher numbers of predators.…”

“…Differential selective pressure in different stages of colonisation might explain why in some cases urban individuals show similar risk-taking to their rural counterparts (e.g. 82,84,88 ). Long-term and population genetics data alongside behavioural assessments are needed to assess if and how such a shift in favoured conditions takes place.…”

Urban fox squirrels exhibit tolerance to humans but respond to stimuli from natural predators

“…Our results from the trials conducted without playbacks also support our assumption that squirrels in urban areas were habituated to human presence whereas those in less urban areas were not. Similar to most other studies in terrestrial animals (Samia et al, 2015) and in studies specifically in tree squirrels (McCleery, 2009;Engelhardt and Weladji, 2011;Sarno et al, 2015;Uchida et al, 2020), we found that squirrels in urban areas exhibited a shorter FAD and FID, lower probability to climb a tree to escape the human observer, and a shorter latency to resume typical behavior following the trial, although only FID was significantly different. Focusing only our trials without playbacks, our results are similar to Uchida et al (2019) as they suggest that the reduction in FID that we observed in urban squirrels is due to both reduced vigilance and habituation to humans given that we found a lower FAD (vigilance) and FID (habituation) in squirrels in the urban areas.…”

Behavior Change in Urban Mammals: A Systematic Review

“…A study in New York, United States, found that 90% of urban gray squirrels increased their FID when approached by humans that veered off the sidewalk and looked at them, while squirrels from the same population did not increase FID if approaching humans remained on the sidewalk (Bateman and Fleming, 2014). Likewise, urban Eurasian red squirrels demonstrated the ability to assess risk levels of various approaching objects (e.g., humans and conspecific decoys) and modulated their FID accordingly (Uchida et al, 2019(Uchida et al, , 2020. Finally, a study on Australian fur seals (Arctocephalus pusillus doriferus) found that seals modulated their alert response based on vessel type and whether or not vessels conformed with mandated approach distance thresholds-indicating that the seals learned the legal distance ships were able to approach (Speakman et al, 2020).…”