Faint spring sunlight breaks through the clouds as black bears and grizzly bears begin to emerge from winter dens. The shifting weather and warmer temperatures signal that food is available again.
Although a bear’s winter sleep is not as deep as a true hibernation, during torpor their body temperature drops, oxygen consumption declines, heart rate falls, and they do not urinate or defecate. When they leave their den, they will have hibernated for about five months, having lost a large percentage of body fat over that time (up to 25% of their body weight for black bears and up to 33% of their body weight for grizzly bears).
This massive weight loss makes it imperative that the bear finds food quickly. While classified as carnivores, grizzly bears and black bears are actually omnivores and opportunistically eat a wide variety of foods with diet varying depending on the season and location.
Spring
Image: Jérémy Mathieu
The spring diet is dominated by intertidal creatures and vegetation such as skunk cabbage, horsetail, cow parsnip, and sedges.
In places like Khutzeymateen Inlet, Lyngby’s sedge dominates the intertidal zone of the estuary, drawing grizzly bears to feed. This herbaceous plant resembling a grass has a very high crude protein content – up to 25% raw protein – and is thus an important source of nutrients for bears emerging from hibernation.
Summer
Image: Jérémy Mathieu
The summer months bring a bounty of berries. Salmonberry, huckleberry, red elderberry, and devil’s club, among others, are favourites for their high sugar and lipid contents. Seeds from these plants are later spread in bears’ droppings, which is an important aspect of seed dispersal in temperate coastal ecosystem.
Coastal bears will also continue to roam the shoreline at low tide in search of intertidal delicacies such as crustaceans, barnacles, and mussels. The ease with which these powerful animals can flip over large rocks in search of crabs is astounding to witness.
Fall
Image: Val Shore
The fall season brings the return of salmon to coastal streams and the chance for grizzly bears and black bears to bulk up.
Timing of the salmon run can vary by species and by area; for instance, July and August mark the height of the salmon run at Pack Creek and Anan Creek in Southeast Alaska, compared to a later peak on the central coast of British Columbia (also known as the Great Bear Rainforest). Regardless of timing, salmon undergo physical adaptations to transition back to a freshwater environment as they await rains to raise the waters to sufficient levels to allow access to spawning grounds upstream. This period of abundance attracts bears back to the estuary to feed and triggers hyperphagia (excessive eating and drinking) which can result in the consumption of 20,000 calories per day in preparation for winter.
Extremely rich in fat and protein, salmon provide the crucial energy and nutrients required for a bear’s continued health and survival. Fish heads, skin, and eggs are particularly coveted. Bears must fatten up quickly as a large body mass is the deciding factor on making it through hibernation and, for females, their ability to reproduce.
The relationship between salmon and bears is very important – and not just for bears’ nourishment! Salmon are a key species and the transportation of their carcasses from the river into the forest is a major nitrogen source to sustain the surrounding environment in which bears and other wildlife reside. Read more about the life cycle of a pacific salmon.
Winter
Image: Jérémy Mathieu
As temperatures begin to drop and food sources become scarce, bears will begin entering their dens for hibernation. With full bellies and healthy fat reserves, they’ll settle down to sleep with the resources needed to survive the following months until spring dawns and the cycle begins anew.
