Long-term distribution responses of a migratory caribou herd to human disturbance

Caribou and reindeer (Rangifer spp.) are known to respond negatively to human activities. Disturbance stimuli can result in short-term behavioural responses or the abandonment of portions of seasonal range. There is relatively little understanding, however, of the ability of caribou to adapt or habituate to long-term human-caused disturbance. We fit species distribution models to 27 years of location data collected for the Porcupine caribou herd (Alaska, USA; Yukon and Northwest Territories, Canada) during winter. We used a novel technique to quantify the avoidance responses and zone of influence associated with human settlements, main roads and minor disturbance features including wells, trails, and seismic lines. We hypothesised that during the early period of monitoring (1985-1998), caribou would demonstrate a greater sensitivity to human disturbance and a larger zone of influence relative to industrial development. Consistent with the assumed level and timing of disturbance, caribou demonstrated the strongest avoidance response to settlements, followed by main roads and minor disturbance features. The data suggested that avoidance, noted as the zone of influence, was less during the more recent time period (1999-2012), but still relatively large when compared to the reported disturbance responses of other populations of Rangifer. A precise habituation response was obscured by uncertainty in the data describing human activities and variation in the distribution and population dynamics of the herd for such an extensive time period. These results suggest that the large-scale behavioural responses of wide-ranging mammals to disturbance stimuli are dynamic. The study of such responses requires accurate data describing human activities as well as long-term monitoring and periodic evaluation.