Study
Hibernation in black bears: independence of metabolic suppression from body temperature
Tøien, Øivind; Blake, John; Edgar, Dale M.; Grahn, Dennis A.; Heller, H. Craig; Barnes, Brian M.
Science, 2011
Black bears were housed in artificial dens in undisturbed forest and instrumented to record metabolic rate, body temperature, heart rate and muscle activity continuously through the winter — the measurement that had been missing, because bears are difficult to instrument and had mostly been assessed from body temperature alone.
- Studied in
- Ursus americanus
- Sample size
- 5 black bears monitored through a full hibernation season
Metabolic rate fell to roughly 25% of basal rate while body temperature declined only to about 30–36°C, in slow multi-day cycles. Heart rate dropped dramatically with long pauses between beats during breathing cycles. Metabolic rate remained suppressed for weeks after body temperature returned to normal in spring.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Metabolic suppression in bears is largely independent of body temperature, so a modest temperature drop does not indicate a modest metabolic response.
How NatureHQ reads it
This is the measurement that changed the answer to "do bears hibernate?". The old objection was that a bear’s temperature falls only a few degrees, unlike a ground squirrel dropping near freezing — so bears were said to enter "winter dormancy" instead. Once metabolism was measured directly rather than inferred from temperature, the suppression turned out to be profound. The question was never really about bears; it was about which variable defines the state.
- Five animals in artificial dens, which are not natural dens however undisturbed the site.
- One species; brown and polar bears differ in season length and physiology.
- Instrumentation and prior handling affect an animal whose whole response is to being undisturbed.
Measuring a bear all winter instead of arguing about it
A denning bear’s body temperature falls only a few degrees, where a hibernating ground squirrel approaches freezing. Does that mean bears are not really hibernating?
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: American Association for the Advancement of SciencePublished in Science or Science Advances (AAAS).
doi.org/10.1126/science.1199435
This reference was resolved automatically against Crossref on 2026-08-11.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-10.