April 5, 2011

What Are the Black Bears Doing?

By Naturalist Beth Moore

It is that time of year again when we need to begin thinking about pulling in the winter bird feeders and making other adjustments in preparation for the spring awakening of black bears. This sometimes inspires us to start asking questions about black bear behavior such as: Where have they been all this time? What triggers them to wake up? When can you expect to see one?

To answer the first question, the bears have been sleeping. Coming up for a term to describe what black bears do during the winter time is a topic that has long been debated. Although they sleep in a den for most of the winter, they can be easily aroused (comparatively speaking) and many female black bears, due to a delayed gestation, give birth during the winter months. However, despite showing some activity in their dens, black bears do undergo physiological changes and have pretty nifty adaptations that allow them to go for more than 100 days without eating, drinking, urinating, defecating, or exercising.

First off, their body temperatures drop by about 10° F (which is actually quite a minor drop when compared to a woodchuck whose temperature may drop by 50° F). A bear’s heartbeat drops from an average (when sleeping) of 40-50 beats per minute to eight beats per minute. Bears also do not rely on stored food in their dens nor do they need to exit the den in search of food. Instead, they are able to gain all the sustenance they need by breaking down stored fat and converting it to food and water. This process can supply a sleeping bear with up to 4,000 calories a day! Any urea produced during this process is broken down and the leftover nitrogen is converted into protein. This protein production has been linked to an explanation of how bears are able to maintain their muscles and organ tissues and are able to survive long periods of inactivity without experiencing muscle cramping or degenerative bone loss. Despite a significant weight loss and long period of inactivity, some statistics indicate that as many as 99 percent of sleeping black bears survive until spring. So whether you call it hibernation, dormancy, or seasonal lethargy, it is safe to say that these animals have unique physiological adaptations that allow them remain inactive through the harshest and coldest months.

So, what triggers the bears to wake up and when do they awaken? Although not common, it is possible to see black bears out and about during the winter months, particularly males and females without any young. I can personally account for this behavior as one sunny day during the middle of winter, I encountered a black bear while skiing in Franconia. I am sure you can imagine my surprise. However, I am comfortable with stating that this is not a common occurrence. Most black bears do not leave their dens until early spring. Exactly what triggers the spring awakening is unknown. Studies suggest that it is combination of increasing daylight, increasing temperatures, and the need for food (especially protein) that results in bears waking up.

Although it is hard to believe with all the snow that we have had (it is actually snowing as I write), but spring is here! This means it is time to bring in winter bird feeders and double check the locks on trash receptacles. Although many black bears survive through the winter without eating, they will wake up with food on their minds. Attracting bears into backyards is one way of assuring they will become a nuisance and most likely not survive. So please help keep the bears wild by thinking about the simple changes you can make in your daily life that will help keep the bears foraging for wild (and more natural) food sources.

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