Exaggerated signaling in a solitary mammal: evidence from brown bears ( Ursus arctos )

Abstract Potential exaggeration in animal communication, though rare, challenges assumptions about the reliability of communication systems. While signals typically convey accurate information, some individuals may exaggerate their traits to gain competitive or reproductive advantages. Among mammals, scent and visual marks are primary communication modes, generally constrained by anatomy and expected to reflect body size honestly. However, manipulating these signals could help subadult or subordinate individuals avoid larger rivals. Using Cantabrian brown bears (Ursus arctos) as a model, we investigated exaggerated marking and its frequency. Over 117,552 h of camera-trap monitoring (2021 to 2024) at 14 marking sites, we recorded 164 individual bears. Seven males (4.3%) engaged in potentially exaggerated marking by climbing marking sites or using platforms to mark higher than their natural height. Of these, 57.1% were adults, and 42.9% were subadults. Elevated marking occurred at 14.3% of sites, mostly during the day. These findings suggest that brown bears can manipulate 'index signals' once considered unfakeable, adding complexity to their communication system. This study provides a cautious perspective on the dynamics of exaggerated signaling, offering insights into the evolutionary maintenance of honest communication systems in nature.