5% of Cantabrian brown bears can deceive each other, study suggests

Published on 26/07/2026 - 21:07 GMT+2•Updated 27/07/2026 - 7:11 GMT+2

Humans are not the only mammals capable of deceiving their own kind. That is the conclusion of a study focusing on Cantabrian brown bears, carried out with input from experts at the CSIC, the FAPAS, several Spanish and European universities and the Principality of Asturias.

The study published in the 'Journal of Mammalogy' (source in Spanish) argues that a minority of the bears living among the peaks of León, Asturias and Cantabria may be 'lying' about their true size to avoid having to face larger rivals. How? By using the signs and markings these mammals leave in their surroundings to stake out territory.

Seven males (4.3% of the 164 tracked) left marks at exaggerated heights by climbing or using tree trunks or other kinds of platforms to leave their mark higher than their real size would allow. Of these, 57.1% were adults and 42.9% subadults. "These results suggest that brown bears can manipulate index signals that were previously thought impossible to fake, which adds complexity to their communication system," the authors summarise.

To investigate this behaviour, the team monitored 14 marking sites in the Cantabrian Mountains over 117,552 hours of recording between 2021 and 2024. The results showed that these crafty seven males climbed trees to leave chemical and visual signals higher than their real height would allow.

Brown bears usually leave their marks at the maximum height they can reach when standing upright on their hind legs, around two metres off the ground. However, the researchers observed a visual mark three metres up, a height no animal standing on the ground could reach. The discovery of a broken branch just below the mark suggests the animal climbed up to make it.

"For a non-dominant male or a young individual, this strategy could offer advantages since, by appearing larger, they could deter bigger rivals, reducing the likelihood of a direct confrontation, avoiding the costs this may entail and even increasing their reproductive opportunities. It is a strategy reminiscent of deceptive behaviour described in other mammals, but one that has never before been documented in bears," says researcher Vincenzo Penteriani from the National Museum of Natural Sciences.

Nevertheless, he and his colleagues are cautious about labelling 'Ursus arctos' as a fundamentally dishonest species, given that the 'tricks' identified are few and occur only in very specific parts of the areas studied. "Our work highlights a fascinating behavioural capacity in bears that justifies further observational and experimental studies," Penteriani says.

Spain's two brown bear populations, in the Cantabrian Mountains and the Pyrenees, now number more than 400 animals after coming close to extinction in the 1970s and 1980s. Although these bears remain endangered, they have moved out of the critically endangered category thanks to conservation efforts.