Scented messages from silent intruders: experimental insights into otter territoriality

Abstract Olfactory communication is central to social interactions and territoriality in mammals, yet the behavioural responses of scent-mark receivers remain poorly understood. We manipulated the scent landscape at Eurasian otter (Lutra lutra) latrines to experimentally examine how otters respond behaviourally to changes in the scent environment at marking sites. Specifically, we examined whether otters adjust their visitation and marking activity in response to (i) the experimental removal of their own spraints and (ii) the addition of foreign spraints from conspecifics, following an initial control phase without manipulation. Using video monitoring, we recorded 217 behavioural events across treatments. The addition of foreign spraints triggered a rapid increase in both visitation and marking within the first 24 h, whereas spraint removal elicited no change relative to controls. Olfactory exploration dominated behavioural responses, while overmarking and social interactions were rare. These findings indicate that otters respond flexibly to changes in scent cues, prioritizing information gathering over overt territoriality. The rapid response to foreign spraints suggests that otters regularly patrol key marking sites, enabling them to detect novel signals almost immediately. Overall, our results highlight olfactory investigation as an adaptive, low-cost strategy for maintaining social awareness and territorial control.