Humans are not the only mammals capable of deceiving their own kind, according to a new study focusing on brown bears in the Cantabrian Mountains. The research, which was published in the Journal of Mammalogy, was carried out through a collaboration involving experts from the CSIC, FAPAS, the Principality of Asturias, and several European and Spanish universities. The findings suggest that a minority of bears spread across the peaks of León, Asturias, and Cantabria may be intentionally misrepresenting their true size to avoid facing larger, more dominant rivals.
To investigate this behavior, the research team monitored 14 marking sites in the Cantabrian Mountains over a period spanning 2021 to 2024. The study involved the analysis of 117,552 hours of footage. The results identified seven male bears—which accounts for 4.3% of the 164 tracked individuals—that made markings at heights that were unusually high. These bears achieved this by climbing trees or using other platforms to leave their trace at a height greater than their actual physical size would allow. Of these seven cunning males, 57.1% were adults and 42.9% were young bears.
Typically, brown bears leave their territorial marks at the maximum height they can reach while standing upright on their hind legs, which is usually around two metres. However, the researchers observed visual signals at three metres, a height that is physically unattainable for any animal standing on the ground. The discovery of a broken branch located just below these marks suggests that the bears climbed up to create them. The authors of the paper conclude that these results suggest brown bears can manipulate index signals that were previously considered impossible to fake, adding significant complexity to their communication system.
Vincenzo Penteriani, a researcher at the National Museum of Natural Sciences, explained the strategic advantage of this behavior. For a young individual or a non-dominant male, this strategy could provide distinct advantages. By appearing larger, they could deter bigger rivals, thereby reducing the likelihood of a direct confrontation and avoiding the costs it may entail, while potentially increasing their reproductive opportunities. While this is a strategy that recalls cases of deception described in other mammals, it had never been documented in bears until now.
Despite these findings, Penteriani and his colleagues remain cautious about branding the species, Ursus arctos, as a dishonest species as a rule. They noted that the tricks identified are rare and occur only in very specific parts of the areas studied. Penteriani emphasized that the work highlights a fascinating behavioral capacity in bears that justifies carrying out more observational and experimental studies in the future.
Spain’s two brown bear populations, the Cantabrian and the Pyrenean, have seen a significant recovery, now numbering more than 400 animals after skirting extinction in the 1970s and 1980s. Although these bears remain endangered, they have successfully left the critically endangered category thanks to the ongoing efforts of conservationists.
