Urbanization has caused significant behavioural modifications in wild animals. Change in anti-predator behaviour is the most widespread example across different taxa in urban areas, which is probably due to a decrease in predation pressure and habituation towards humans. Seasonality or phenology has also been modified by urbanization since some resources in urban environments are highly controlled, for example, artificial feeding. Under natural conditions, anti-predator responses vary with seasonal variability in environmental and individual conditions. However, resource stability possibly reduces the seasonality of anti-predator behaviours in urban animals. Here, we compare the seasonal difference of flight initiation distance (FID), a measurement of anti-predator response, in Eurasian red squirrels Sciurus vulgaris between urban and rural areas in the Tokachi region, Hokkaido, Japan. Rural squirrels possessed FIDs two to three times longer than those of urban squirrels. We also found squirrels in rural areas lowered FID in autumn, but no seasonal difference was observed in urban squirrels. Our results suggest that continuous supplementary feeding may have buffered the seasonality in anti-predator response. In addition, strong habituation to humans may allow urban red squirrels to correctly assess human activity as benign rather than reacting unnecessarily.

Increased boldness is one of the most prevalent behavioral modifications seen in urban animals and is thought to be a coping response to anthropogenic environmental alterations. Most previous studies have shown enhanced boldness manifested as changes in responses to humans approaching, such as reductions in flight initiation distance (FID). However, this includes two confounding factors related to “boldness,” that is, reduction of vigilance and habituation to humans. Confounding these totally different processes could lead to our misunderstanding of urban adaptation and how to properly manage urban wildlife. Here, we propose a simple framework to separate the two processes using two flight distance measures toward different approaching threats. We considered that the distance at which targeted individuals noticed an approaching object (i.e., alert distance, AD) was related to vigilance, whereas FID represented risk assessment, which is related to habituation. We applied a predictive framework using AD and FID to Eurasian red squirrels’ responses to multiple threats of different risk levels (i.e., humans, model predators, and novel objects). AD was shorter in urban individuals compared with rural ones but not different among the approaching objects. FID was shorter in urban individuals and also varied among the objects with the shortest FID toward humans, whereas rural individuals showed similar FID to the different objects. These results suggest that, although urban individuals showed reduced vigilance, they could still assess different risk levels. Our framework can easily be applied to many animals and could significantly improve our understanding of wild animals’ adaptations to urban environments.

A phylogeographical study of the Russian (Siberian) flying squirrel (Pteromys volans) was carried out using the complete mitochondrial (mt) cytochrome b gene sequences with special reference to the refugia theory for the arboreal traits of this species. We examined 31 specimens from 24 localities, resulting in 28 haplotypes. One breeding specimen with a unique haplotype from Hokkaido, Japan was included in the phylogenetic analysis. There were three mtDNA lineages: Hokkaido, Far Eastern, and northern Eurasia. Divergence data among lineages demonstrated that the Hokkaido group separated from the other groups during the Holsteinian interglacial. The phylogeographical pattern of P. volans is different from that previously reported for terrestrial rodents associated with treeless habitats. Unlike grasslands, forests decreased during glaciation and moved southward because of the cold and arid environmental conditions. The glacial refugia of P. volans would have been associated with forest dynamics in the Pleistocene.

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.

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