With a metabolic chemistry scientists have described as marvelous, Black Bears throughout the Shuswap spend the winter in hibernation.
Snuggly tucked beneath the snow in a hole they’ve excavated under a tree, dug into a side hill, or nestled within a tree cavity high above the ground, the bears do not eat, drink, defecate, or urinate for up to five months. Just imagine…
Pregnant mothers birth in their winter dens and then nourish their cubs solely with their milk. Everything baby bears need to develop as fetuses, and then as youngsters, comes from their hibernating mother. Adding to the wonder, these adult female bears and their babies emerge from their dens in the spring in good body condition with muscle strength and bone density intact.
Unlike many other hibernating mammals, both black and grizzly bears maintain a hibernating body temperature that is only slightly reduced from their active-season normal. This allows the chemical reactions within their bodies to keep quite active and to continue building and rebuilding both muscle and bone. To keep both warm and metabolically active during this long-fast, the adult bears require fat as fuel, lots of fat.
In fact, over-eating whenever they can during the warm months is key to a bear’s survival through these winter-long hibernation fasts. From digging roots and finding the best berry patches to scavenging dead salmon, bears relentlessly explore their territories for fat-producing calories. A skinny bear in autumn will have little chance of seeing another spring.
But what about water, how do hibernating adult bears survive without drinking? Again, the key is body fat. When this fat is metabolized to release energy to keep the bear warm, it produces water as a by-product. This “metabolic water” keeps the bear hydrated and allows the females to produce milk.
I’ve had the rare opportunity of visiting many black bear dens in the early spring as part of a radio-telemetry study of bear mortality in the Rocky and Columbia mountains. Guided by signals from a female’s radio-collar, we quietly followed the signals until we found the den’s entrance leading either beneath the snow or inside or under a tree. Occasionally, we could hear the sounds of the cubs coming through the snow as they suckled on their mother and squabbled with each other. Hearing them just a metre or two away was thrilling proof that the cubs had been born. These cubs had made it through the worst part of the winter and in a few weeks, would venture into the outside world with a fit and healthy mother ready to protect them.
Anyone who has been bedridden for more than a few days knows how quickly we can lose our strength and bone density by not using our muscles. The ability of bears to be inactive for long periods but remain healthy, has attracted attention of medical researchers looking for ways to reduce the negative effect of inactivity on humans. What could we learn from chemistry of bear hibernation that could lead to better treatments for the mobility impaired people?
Looking to the future as we begin to reach out from Earth through space travel, what can we learn from hibernating bears that might help astronauts cope with the muscle and bone degeneration that could accompany prolonged space travel?
That also would be a marvel!
