Cantabrian Brown Bears Size-Deception Research

An international research team monitored 164 brown bears (Ursus arctos) across 14 marking sites in Spain’s Cantabrian Mountains between 2021 and 2024, accumulating over 117,000 hours of camera‑trap footage. Initial analysis showed that about 5 % of the observed bears placed visual and scent marks on platforms or high points beyond their natural reach, creating the appearance of a larger animal. This deceptive signalling was reported as the first documented case of intentional size exaggeration in bears and was linked to rival deterrence and potential reproductive benefits.

A follow‑up study published in 2026 refined these findings, identifying seven male bears (4.3 % of the sample) – 57 % adults and 43 % juveniles – that climbed trees or used purpose‑built platforms to deposit marks at roughly three metres, well above the typical two‑metre maximum reachable while standing. The authors, collaborating with the Spanish National Research Council (CSIC), the FAPAS institute, several universities, and the Principality of Asturias, reaffirmed that bears deliberately inflate the perceived size of their signals to intimidate rivals, suggesting the behaviour may be more widespread among mammals.

Separately, a bear was observed running at night on a road near Otsagabia and Ezkaroze in northern Spain. Local authorities responded by allocating funds for protective measures—including guard dogs, shelters and shepherds—to safeguard livestock from possible bear encounters.