Combined effects of fine-scale intensity and spatial extent of exposure to outdoor recreation shape wildlife responses and tolerance to human activity

Outdoor recreational activities and nature-based tourism are rapidly expanding, both in intensity and space. Even non-consumptive activities can have adverse effects by altering animal behaviour and physiology, but wildlife can also develop behavioural tolerance to humans and adjust to human activities. However, few general patterns have emerged, likely due to incomplete knowledge of the factors that modulate wildlife responses. For example, it remains unclear how fine-scale intensity and spatial extent of exposure to outdoor recreational activities influence disturbance effects on wildlife. Here, we investigated how the combined effects of current on-site visitor numbers, the extent of areas used by humans, such as around picnic areas, within animal's home ranges and the proximity of animals' activity centres to main recreational infrastructure, such as main hiking trails, affect behavioural and physiological responses to outdoor activity. We used Alpine marmots Marmota marmota in Stelvio National Park (central Italian Alps) as a case study. Marmots occupying territories with low human area use and with activity centres located farther from the main hiking trail in the study area increased anti-predator behaviours and decreased foraging during higher visitor presence. In contrast, marmots from territories with higher area use and/or activity centres closer to the main trail were more tolerant. Stress levels assessed through faecal cortisol metabolites (FCMs) mirrored this pattern, but high uncertainty around FCMs estimates suggests cautious interpretation. This case study demonstrates that wildlife responsiveness to outdoor activity can depend on multiple interacting factors, highlighting the importance of context-specific impact assessment and targeted mitigation strategies