I’ve recently been in bear territory in the heart of Alaska and have a whole new respect for these incredible mammals.
As part of a land expedition off our cruise ship we went in search of these animals. We saw them in rivers catching salmon, hunting for food and even crossing the road.
Bears are solitary animals and unless a mother has a cub they are usually on their own. My first sighting of a bear was in a river as it looked for salmon. Then by chance after exploring the Mendenhall Glacier I came across a mother and cub foraging in the undergrowth for tree roots. We watched them eat, unperturbed by their audience. Then, on our way back to the ship a bear crossed the road in front of us, then made a mercy dash into this backyard.
Getting ready for winter
In late autumn, bears can become ferocious scavengers. The salmon have almost stopped running, the berries are gone so they resort to garbage in people’s back yards in an effort to putting on weight to survive the long winter hibernation.
Surprisingly, their diet is 80% plant-based. However, they are also partial to the odd salmon when they are running the rivers from summer through early autumn. It’s not uncommon to see a bear in the stream feeding, sometime pulling as many as 40 fish a day. However, if they are not starving they are discerning eaters. They smell the fish and if it’s a female they’ll push her belly and slurp the eggs, before biting it’s head off and throwing it on the bank for the cubs to eat.
Are bears to be feared?
I thought all bears were to be feared, but this is not entirely true. We only saw black bears and apparently their personalities are like that of a Labrador dog. Their first line of defence when startled is to retreat, that’s why almost every Alaskan household has a dog.
However, brown bears can be more aggressive. They typically don’t harm unless they feel threatened or someone comes between them and their offspring. But, it’s the grizzly bears, a sub-species of the brown bear that really should be avoided.
The advice we were given was if you do come in contact with a bear, talk to it, do not run as it will out run you at a speed of about 50 kilometres an hour. And remember it found you, you didn’t find it. They have the most incredible sense of smell and can sniff you out up to 12 kilometres away.
The denning (or hibernation) period
What makes this mammal even more fascinating is its denning period. They hibernate not because of the cold, but because of a lack of food during the winter months. In late November as the days shorten and the temperature drops a bear make its den often under a tree stump. However, black bears have been known to hibernate in a people’s basement without them knowing.
As part of the preparation for hibernation bears eat indigestible plant to purge their digestive tracts and form a rectal plug. The faecal plug is simply faeces that have remained in the intestine for a long time. As a result, bears do not urinate or defecate during hibernation. Instead, they reabsorbs their waste in the form of proteins.
When they drift into sleep their heart rate reduces from 40-50 beats per minute to 7-8 beats per minute. During this time, they lose about 10-15 % of their body weight. They also produce a hormone called leptin that decreases their appetite and stops them feeling hungry. Although we refer to bears hibernating, they only go into a deep sleep called a torpor. They are on alert and should they be in danger they will awake. Their temperature drops by only 7 or 8 degrees centigrade (instead of freezing like a ground squirrel) which is in true hibernation.
Did you know bears give birth while asleep, hibernating?
Bears burn about 4,000 calories a day while in torpor so need to be plump before going to sleep. If the female bear goes into hibernation pregnant, she will only produce a cub is she has enough stored energy (fat) to last her and her cubs through the winter. If she does not have enough stored energy, she will reabsorb the embryo and will not give birth that year. This adaptation works to ensure female bears survive the long winters as they can lose up to 40% of their body weight during the winter and lactating.
If her pregnancy continues she will give birth after approximately 30-weeks, at the end of January. She will deliver her cub or cubs when she is still asleep and they will suckle from her until she wakes up in spring. At birth, they will weigh between 300 -500 grams and when they exit the den the cubs will be between 4-5 kilograms. The mother will still be lethargic from the hibernation and will not roam far from the den. She will nurse them for about 30 weeks and the cubs will stay with her until they are about 18 -24 months old.
Slowly, slowly, their energy comes back and they begin to forage again on spring berries and foliage and this whole phenomenal start over again.