Behavioural responses of Newfoundland woodland caribou to predator cues

Insular Newfoundland woodland caribou (Rangifer tarandus) have experienced tremendous population declines since the early 2000s, attributable to density-dependent processes mediated largely by predation. Given the diversity of island predators (black bears, coyotes, lynx and bald eagles), caribou are thought to perceive and react to the different predators in a manner that accordingly minimizes the probability of death and maximizes benefits of fitness-enhancing activities. The presence of predators requires prey species to divert energy resources from foraging and feeding behaviours to vigilance and predator avoidance behaviours. This study was designed to identify and describe caribou behavioural responses to predator encounters. Experimental approach trials (n=137) were employed in the calving region of the Middle Ridge caribou herd (central Newfoundland) in order to simulate different predator visual cues and to elicit corresponding caribou flight responses. Approach trials encompassed the time period when calf mortality by predation is highest. The flight initiation distance of caribou (the distance between approacher and caribou at the moment of initial flight) was found to differ in accordance with the colour of clothing (tan or black) but not the movement mode (walk or crawl) employed by human experimenters. Flight initiation distance was greater in response to black approaches and was greatest during the two week calving period from late May to mid June. There was little evidence that vegetation resources influenced the decision to remain or flee; however this finding may reflect the calving range fidelity of caribou to areas of consistent forage quality. This study yields important findings concerning variation in predator avoidance behaviour of caribou in response to historical i.e., black bear, Ursus americanus) and novel (i.e., coyote, Canis latrans) predators. Differential behavioural responses to predators are particularly important to understand as rapidly growing anthropogenic landscape development and use is leading to increased predator encounters