Grizzlies have an amazing digestive system

Grizzlies are always hungry. It’s no wonder, because of a five month hibernation fast, they must go into the den at least 150 pounds over the weight from which they emerge. This large, aggressive omnivore (meat and vegetation eater) is in reality a very poor predator. Meat is preferred, but not often an option. As a result, the animal consumes a wide variety of food stuffs.

Their favorite food is ground squirrels, which they vigorously dig for. Other meat sources may include fish, newborn mammals, and carrion from winter kill. However, 70% of their diet is grass. It needs to be moist and at least 4 inches long because they graze with a sideways motion of the head. It’s interesting to watch them grazing on a hillside like cattle. Other foods are insects, buds, berries, nuts, and roots.

That hump between the shoulders is a massive muscle for digging, which they are masters at. They require a massive 24,000 calories a day, and their digestive tract is 80 feet long (10 feet for each foot of body length – humans have 4 feet for every foot of height). This great length of gut enables the digestion of a truly great variety of food stuffs. The bear is most aggressive when guarding a carcass, or when a sow is guarding her cubs. The bear is also very fast. Grizzlies can cover 50 yards in 3 seconds. My wife and I watched one ambling along, when suddenly the bear became alert and was off. It was amazing how fast that beast covered the ground and was gone!

Once, in a Canadian campground, I was sitting and reading to my wife. Our backs were toward the woods. A man came up the trail, on his way to the restroom. He asked if we had enjoyed our visitor. Evidently, a Grizzly had come out of the woods and sat behind us, unbeknown to us. It then, when seeing the man approaching, had returned into the trees.

 

Red Squirrels, Grizzlies, and White-Bark Pine

by Dave Hanks

There is a very interesting triangle arrangement between the above three species. White-Bark Pine nuts are high in protein and fats. The nut’s make-up is about 74 percent of these two ingredients. Protein and fat is extremely important to both bears and squirrels. Of course, protein is important to all animals (humans included), but the fat is especially important for winter survival for species that hibernate or survive cold weather. Eskimos require much fat in their diet to prevent Fat Deficiency Syndrome (weakness, nausea, and blindness). Extreme cold necessitates a different diet than what we would think to be healthy.

Anyway, the Red Squirrel cuts down the pine nuts and stores them in giant middens (caches) – usually in softer ground at the base of a tree. These storage spots may contain as much as a three year supply of nuts for winter use. Then, enter the bear on the scene, especially Grizzlies. In the fall, the bear, which requires 24,000 calories a day most of the time, is in an increased feeding mode in preparation for winter torpor. They move up to the White-Bark Pine zone in search of nuts, a very rich and important food source for the bear. They can not climb trees to reach the nuts, however, the squirrel has solved that problem, and the bear simply has to dig the nuts out of the squirrel’s middens.

Trees can’t travel, but animals can and Grizzlies spread pine seeds in their scats – a benefit to the tree population. Squirrel populations do not become excessive because the Grizzly is a limiting factor on squirrel numbers when nut cycles peak. This is actually a benefit to the squirrel, because it keeps competition in check. When nuts are on the low end of their cycling, the bears are forced to eat more grass – which requires a daily intake of 90 pounds to meet their dietary needs.

I find symbiotic relationships most fascinating, and this triangular arrangement is no exception.

A Red Squirrel: Master of the nut cache