Regional-dependent tolerance to humans: A multi-country comparison of horizontal and vertical escape distance in arboreal squirrels

As urbanisation increases, wildlife is more likely to be exposed to humans. Although human disturbance is the main cause of biodiversity loss, some wildlife thrives in anthropogenic environments. Such species show increased behavioural tolerance to humans, which plays an important role in human-wildlife coexistence. However, whether wildlife modulates tolerance differently between regions and cities is inadequately understood. Understanding how animals behaviourally modulate their tolerance to humans at the larger geographical scale can provide useful information to predict behavioural adaptations to urbanisation and adequate management actions for conservation. We examined alert distance (AD), flight initiation distance (FID), and vertical escape distance (VED) in Eurasian red squirrels (Sciurus vulgaris) in four countries (Finland, Germany, Japan, and the UK). Linear mixed models with Tukey’s multicomparisons showed that all tolerance measures varied between countries. We subsequently analysed the relationship between site-scale environmental variables (vegetation conditions, presence of artificial feeding, and human population density) and tolerance behaviours separately by country. We found that squirrels were more tolerant in sites with taller trees and more underbrush cover in the UK, and more tolerant in sites with artificial feeding in Japan, while environmental variables were not associated with squirrels’ tolerance in Finland and Germany. Our results indicated that regional forms of environmental factors and human-squirrel interactions play a key role in tolerance modification at the larger spatial scale. Our study suggests the importance of considering regional-dependent relationships between tolerance behaviours and environmental characteristics for urban wildlife conservation and management.