Adult males mark trees during the breeding season by scratching and biting the bark 

These markings help us to locate the species' breeding grounds, crucial for successful conservation plans

For the first time, a study provides evidence that, in addition to communication through chemical signals, brown bears, Ursus arctos, make visual signals by tearing the bark off certain trees. This research, led by the Museo Nacional de Ciencias Naturales (MNCN) and involving the Estación Biológica de Doñana (EBD) and the Instituto Mixto de Investigación en Biodiversidad (IMIB), all part of the CSIC, shows that the visual signals are made exclusively by adult males and are only linked to the reproductive needs of the species.

For this article, published in the Journal of Mammalogy, the team worked with the brown bear population in the Cantabrian mountain range using photo and video trapping. The images obtained have allowed to analyse the behaviour of several dozen individuals, including the 13 adult males responsible for leaving marks on trees. "For a long time, communication between mammals was considered to be essentially limited to chemical and acoustic signaling," says MNCN researcher Vincenzo Penteriani.  "This experimental work offers, for the first time, evidence of the existence of a new communication channel for this species: visual signaling by removing part of the bark of the trunk of particularly visible trees," he continues.

These visual markings, made by scratching and biting the bark, appear to have a very specific meaning as they are only made by adult males during the mating season. The researchers suggest that the marks could provide information such as the size of the individual, which is ultimately a way of making the dominance status known of each male in search of mating opportunities. This is information that complements the information provided by the chemical signals that were already known.

"Knowing the meaning of this form of communication not only represents an advance in our understanding of animal communication, but can also be used by us to easily locate areas frequented by bears during the mating season. This is crucial information for conservation and management actions for the species," says Penteriani. 

Reference: V. Penteriani, L. Etchart, E. González-Bernardo, A. Hartasánchez, D. Falcinelli, H. Ruiz-Villar, A. Morales-González, M.M Delgado. 2023 Sex-, age-, and time-specific visual communication in brown bears. Journal of Mammalogy. DOI: https://doi.org/10.1093/jmammal/gyac126

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