Unwilling to leave, unable to stay: Mechanism of plasticity in site fidelity as a rewarding tactic in changing environments

Context Home-ranging is common among animal species, as site fidelity facilitates cognitive map development and promotes efficient habitat use. The adaptive value of site fidelity, however, should decline as environmental conditions change, yet empirical evidence remains limited. Objectives We investigated how fire and forest harvesting affect home-range stability in boreal caribou, a species typically exhibiting strong site fidelity. We then identified conditions where fidelity increases mortality risk and when shifting home ranges becomes advantageous. Most deaths were caused by wolves, a predator that benefits from forest disturbance. Methods We monitored 331 GPS-collared caribou across 667,000 km² of boreal forest. Forest harvesting and fire disturbance levels were related to indices of home-range fidelity derived from the spatial proximity of locations across successive years. Survival was then evaluated in relation to habitat conditions following home-range adjustment. Results Caribou increasingly altered their home ranges as local disturbance intensified. This reduced fidelity increased survival, but only in highly disturbed landscapes. Individuals remaining in high-disturbance areas had lower survival than those that moved into similarly disturbed areas. Conversely, high fidelity in low-disturbance environments was associated with relatively high survival. Conclusions These results show that site fidelity can become maladaptive under shifting risk regimes, whereas reduced fidelity enables adaptive exploratory movements. Our findings clarify how behavioral responses to disturbance translate into demographic outcomes. From a conservation perspective, protecting habitats currently used by caribou and maintaining connectivity among them is essential, as strong site fidelity can yield positive survival outcomes in low-disturbance landscapes.