Virginia Tech researchers have uncovered new evidence that black bear hibernation is governed by a complex interaction between temperature, daylight, and the animals’ internal physiological state. The findings challenge the long-standing view that bears simply enter and leave hibernation in response to falling and rising temperatures. Instead, the study suggests that American black bears interpret multiple environmental signals at once, and that climate change could disrupt the relationship between those signals in ways that alter bear behavior, food-seeking patterns, and encounters with people.
The research, led by Brogan Holcombe, a doctoral student in Virginia Tech’s Department of Fish and Wildlife Conservation, analyzed more than 22,000 hours of continuous video recorded at the university’s Black Bear Research Center. Holcombe conducted the work with Marcella Kelly, a professor in the Department of Fish and Wildlife Conservation, and Bernardo Mesa-Cruz, who earned his Ph.D. from Virginia Tech in 2018. The researchers focused on four wild, pregnant female black bears observed across several stages of the annual hibernation cycle. Their goal was to determine how the animals’ behavior changed as environmental conditions shifted before, during, and after hibernation.
The team classified 45 distinct behaviors from the video recordings, creating a detailed behavioral record that went well beyond simply noting whether a bear was awake or asleep. Movements, posture changes, feeding-related activity, grooming, den behavior, and other forms of physical activity were tracked and compared with ambient temperature, photoperiod, and the bears’ position within the hibernation cycle. Photoperiod refers to the duration of daylight and darkness over a 24-hour period. Unlike temperature, which can vary dramatically from day to day, photoperiod changes predictably with the seasons and provides animals with a stable astronomical signal of the time of year.
The results showed that temperature and day length both influenced bear activity, but their effects were not uniform throughout hibernation. Temperature appeared to be particularly important as bears entered hibernation, when they were transitioning from normal autumn activity into a state of prolonged dormancy. During other phases, especially the periods surrounding pre-hibernation feeding and den emergence, activity was more strongly associated with the combined effects of temperature and photoperiod. This interaction indicates that bears may use temperature to assess immediate environmental conditions while relying on day length to place those conditions within a broader seasonal context.
Hibernation in black bears is physiologically unusual compared with the deep torpor experienced by many smaller mammals. Bears can reduce their metabolic rate, heart rate, and body temperature while remaining capable of waking and moving when necessary. They do not typically eat, drink, urinate, or defecate throughout the winter denning period, relying instead on fat accumulated during the preceding months. Pregnant females also give birth and nurse cubs inside the den. Because this prolonged period of fasting and reduced activity is closely tied to energy conservation, even modest changes in the timing or frequency of movement could have consequences for survival, reproduction, and the timing of spring emergence.
The study’s findings are especially significant because the seasonal cues used by bears may no longer change in synchrony. Climate warming can raise autumn and winter temperatures without altering the length of the day. A bear may therefore experience conditions that feel biologically like spring or late autumn while the photoperiod continues to signal winter. This potential uncoupling of environmental cues could produce what ecologists call a phenological mismatch, in which an animal’s behavior no longer aligns with the seasonal availability of food, shelter, or other ecological resources.
“As temperatures rise, bears may become more active during times when they would traditionally remain dormant,” Holcombe wrote in the study. Increased winter activity could require bears to draw more heavily on stored fat, particularly if they leave the den repeatedly or emerge before sufficient natural food becomes available. In areas where natural resources are limited, hungry or prematurely active bears may be more likely to investigate unsecured garbage, bird feeders, livestock areas, or other human-associated food sources. Such behavior can increase the likelihood of property damage, vehicle collisions, and conflicts that are dangerous for both bears and people.
The researchers emphasize that the relationship between climate and hibernation is not as simple as a warmer winter producing a uniformly more active bear population. The impact may depend on when warming occurs, how long it lasts, whether daylight has begun to increase, and what stage of hibernation an individual bear has reached. A brief warm spell during early denning may affect activity differently from sustained warmth near emergence. Pregnancy, body condition, age, and individual behavior may also influence how a bear responds. The study’s sample of four pregnant females provides unusually detailed observations, but the researchers note that broader studies involving more bears, different reproductive states, and multiple landscapes will be important for determining how widely the patterns apply.
The work offers wildlife managers a more precise framework for anticipating changes in bear activity. Monitoring programs could combine temperature records, daylight cycles, den locations, camera-trap observations, and reports of human–bear encounters to identify periods when bears are likely to become active earlier or remain active later. Managers may also use the information to improve public warnings, adjust strategies for reducing access to artificial food, and evaluate whether conservation policies designed around historical hibernation schedules remain effective under changing climate conditions. Understanding when bears are most likely to move through forests or approach developed areas could also help communities reduce attractants before conflict occurs.
Published June 3, 2026, in the Proceedings of the Royal Society B: Biological Sciences, the study is among the first to directly examine the combined influence of ambient temperature and photoperiod on hibernation activity in American black bears. Its central message is that hibernation is controlled by a network of interacting biological and environmental signals rather than by temperature alone. As winters become less predictable, separating those signals could reshape one of the most important seasonal transitions in the black bear’s life. The research provides both a clearer view of bear physiology and an early warning that climate-driven changes in timing may ripple outward through ecosystems and human communities.
Subject of Research: How ambient temperature and photoperiod influence hibernation activity and behavior in American black bears.
Article Title: Untangling the influence of ambient temperature and photoperiod surrounding hibernation activity in American black bears
News Publication Date: June 3, 2026
Web References: https://cnre.vt.edu/ ; https://fishwild.vt.edu/ ; https://royalsocietypublishing.org/rspb/article/293/2072/20260374/481983/Untangling-the-influence-of-ambient-temperature
References: Proceedings of the Royal Society B: Biological Sciences; DOI: 10.1098/rspb.2026.0374
Image Credits: Photo courtesy of Brogan Holcombe
Keywords: American black bears, bear hibernation, photoperiod, ambient temperature, climate change, animal behavior, wildlife conservation, behavioral ecology, phenological mismatch, human–wildlife interactions
