Dominant predator odour triggers caution and eavesdropping behaviour in a mammalian mesopredator

Mesopredators need to satisfy their energetic requirements while avoiding potentially lethal encounters with apex predators. Predators release odours into the environment through natural processes, and many antipredator adaptations are induced by the detection of these scents. We tested whether a mesopredator adjusted its behaviour when it encountered dominant predator odour in an outdoor arena. Eighteen wild-captured stoats (Mustela erminea) were exposed to the body odour of three predators: two previously encountered sympatric apex predators [cat (Felis catus) and ferret (Mustela furo)] and a novel apex predator (African wild dog (Lycaon pictus)). Foraging areas were created that varied in perceived risk, based on the presence or absence of predator odour. Detection of kairomones (chemical cues from predators) triggered cautious inspection and altered the mesopredator's foraging activity. However, in contrast to our predictions, dominant predator odour was an attractant rather than a deterrent; food was consumed earlier in foraging areas with apex predator odour than in unscented controls. Sympatric predator odour elicited the most pronounced behavioural changes, with stoats cautiously approaching, but readily investigating, the odour source. Ferret odour stimulated the most marked changes. Mesopredators may benefit from exploitative eavesdropping as detection of predator odour primes antipredator behaviours, avoids the energetic cost of unnecessary flight and may also help a mesopredator to locate resources. This experiment highlights the role of odour in the assessment of risk and its capacity to alter foraging behaviour by a subordinate member of a predator guild. A predator encounters a myriad of scents when foraging, which can then be used to make inferences about its environment. In an outdoor arena, we tested behavioural responses of stoats to the odour of three dominant predators. Upon detecting the scent of a co-evolved predator (cat or ferret), stoats increased their cautious behaviour, but contrary to our initial prediction, they were attracted to the odour; food was consumed earlier in foraging areas with co-evolved predator odour than in unscented areas, or areas with the scent of a novel predator (African wild dog). Mesopredators 'eavesdropped' on the olfactory communication system of larger predators to reduce an encounter risk while obtaining food resources. Our results have practical applications for wildlife management and also increase our understanding of the role of scent communication in predator assemblages.