Bears adjust their winter alarms for light and heat, but the climate confuses their biological clocks

It is not just the cold that tells the black bear that hibernation time has arrived.

A new study suggests that its body reads two signals together: temperature and day length, as if nature were setting a precise seasonal clock for it.

Researchers analyzed more than 22,000 hours of video recordings of four female American black bears and classified 45 behaviors across different stages associated with hibernation.

The results showed that the effect of temperature interacts with daily light duration in determining activity levels, particularly when preparing to hibernate and when emerging from the den.

The problem lies in the fact that day length changes in a relatively fixed seasonal pattern, while temperatures have become more variable due to climate warming.

As a result, bears may receive conflicting signals: light indicates that winter has begun, while high temperatures suggest that conditions are still suitable for activity.

Researchers warn that rising temperatures may make some bears more active during periods when natural food resources are scarce, potentially driving them to approach populated areas in search of food and increasing the likelihood of human-bear conflicts.

The study does not mean that bears will stop hibernating; rather, it reveals that the timing of hibernation and the surrounding activity patterns are more sensitive to climate than previously thought.