Ever seen a grizzly bear? Well, one might be coming to a doorstep near you.
Author: Cameron Hersey, Edited By: Emilyann Ashford
Grizzly bears are heavily affected by seasonal changes due to global warming forcing them to end hibernation early and hungry, in search for their next meal.
Grizzly bears occupy hibernation not only as a tool to survive harsh winter conditions causing food limitability, but also as a form of energy conservation (2). Sleeping and remaining sedentary are great low energy activities to limit needed food intake on a given day (2). Additionally, this period serves as an excellent time for female bears to give birth to their cubs (2). Hibernation generally begins in late October or November and ends in March to April lasting approximately 5-7 months (3).
Humans are increasingly affecting the rates of global warming and thus the warming of our climatic seasons. Environmental cues such as these temperature changes allow bears to react knowing that it is time to end their hibernation (2). Have you ever had an instance in which you get into a sleep schedule rhythm either due to school or work and start to wake up on your own even before your alarm goes off? This is a similar situation in which a bear’s internal clock works, each year as the temperatures start to drop or rise, the bears recognize that it’s time to get ready to start or end their hibernation period without even knowing what season it may be. If the cues start to change, then the bear's reaction will start to change, in this case reacting to increased temperatures causes the ending hibernation earlier than normal (1).
Few studies have shown Bears ending their hibernation as early as January or February which is 1 to 3 months sooner than we normally see (1). During these earlier months the berries they feed upon have not fully bloomed yet, which causes many bears to wake from hibernation with little food available. This causes bears, of whom require 80 to 90 pounds of food daily (5), to seek far and wide to find needed nutrients, likely bringing them closer to humans, or urban developments. This introduces a cause for concern that there will be an increase of bear to human interactions (fig. 1). While these encounters can occasionally happen during their normal preying time of March or April, we can predict it is much more likely for these encounters to occur as temperature rises due to lack of nutritional availability. The presence of hungry bears will surely bring them to the nearest food source which may very well be a human habitat.
Figure 1: Grizzly bear interaction with human
As mentioned, hibernation is based on environmental cues, food being an example. Bears should remain in their dens until the springtime when flowers and berries are in full bloom for feasting upon. Berries in particular compose a vast amount of the bears diet during these months, and if bears awaken from hibernation too early, berries are not fully grown and ready for consumption via the bear (5). Hibernation is a time for bears to utilize low amounts of energy to remain isolated and even for female bears to give birth to their cubs. Once this hibernation pattern changes, their feeding habits as well as diets will soon change as a result. One such result could be bears ending up searching through trash cans of neighborhoods and towns as shown in figure 2.
Along with increasing bear-human interactions, we are increasing stress on the cubs (2). This stress can occur when den temperatures rise above the optimal hibernation temperature range which increases the bear’s metabolic rate, which in turn increases consumption of stored energy reserves. Since cubs are born during hibernation their food supply and energy stores are limited, causing higher metabolic rate leading to cub deaths (2). Both, human-bear interactions, and cub survival decreases and result in two negative interactions between humans and bears. Full grown bears may be more often victims of firearm deaths causing possible alterations in ecosystems, and on the other hand, humans could be more vulnerable to bear attacks due to proximity.
As we continue to contribute to the increasing temperatures in current times, we are affecting much of the world around us without each consequence being properly understood. Considering outcomes such as coming face to face with a grizzly bear on your property due to global climate change may not be a person's first consideration, but it is happening. In a study conducted in 2018 on the seasonal sensitivity of brown bear denning phenology in response to climatic variability, which was conducted for 69 years, found that years in which warming occurs earlier in spring than average conditions, triggered brown bears first den exit to be premature (2). In other words, this study is indicating their results show, over a period of 12 months a much milder, warmer winter results in bears exiting their dens earlier than usual (2). Additionally, in a study conducted in 2016 on the drivers of hibernation in the brown bear, they found that ambient temperatures of the environment were not changing the body temperature of the bear but instead the temperature of their den causing the bear to become too warm, which resulted in the bears exiting their dens in search of more comfortable temperatures (4).
If we do not consider and search for a future of reducing our carbon emissions, and thus reducing the rate at which global warming is occurring, we will instead look to a future that could have many of us experiencing or knowing of interactions between humans and wild grizzly bears.
Citations
Pigeon, Karine E., et al. “Drivers of Hibernation: Linking Food and Weather to Denning Behaviour of Grizzly Bears.” Behavioral Ecology and Sociobiology, vol. 70, no. 10, June 2016, pp. 1745–1754., doi:10.1007/s00265-016-2180-5.
Delgado, M M, et al. “The Seasonal Sensitivity of Brown Bear Denning Phenology in Response to Climatic Variability.” Frontiers in Zoology, vol. 15, no. 1, Jan. 2018, doi:10.1186/s12983-018-0286-5.
Denning and Hibernation Behavior. (n.d.). Retrieved March 27, 2020, from https://www.nps.gov/yell/learn/nature/denning.htm
Evans, A. L., Singh, N. J., Friebe, A., Arnemo, J. M., Laske, T. G., Fröbert, O., … Blanc, S. (2016). Drivers of hibernation in the brown bear. Frontiers in Zoology, 13(1). doi: 10.1186/s12983-016-0140-6
“Brown Bears.” National Parks Service, U.S. Department of the Interior, www.nps.gov/subjects/bears/brown-bears.htm.