The Season of Denning For Katmai’s Brown Bears
by Ranger Masaki Mizushima of Katmai National Park
It is early October and autumn glazes over Brooks Camp. This is the time of year when change takes place and the transition of the seasons washes over the wilds of Katmai National Park, progressing down to the tip of the Alaskan Peninsula. The tinting browns of blue-joint grass, the deep blood-red of fireweed, and the flaming yellow-orange hues of balsam poplar, birch, and willow indicate the end of yet another year at Brooks Camp. However, it is not the end for Katmai’s brown bears. They will continue their frantic feeding frenzy (hyperphagia) until their food source, primarily salmon, is no more.
As September gives way to October, and October to the approaching freeze of winter, brown bears, with their bellies full of decaying fish, will begin to wander off from Brooks River; maybe an individual one day, a handful the next. However, what determines an individual brown bear’s time to den is an inner biological alarm announcing when each has acquired enough fat reserves to last throughout winter hibernation. Typically, pregnant females and sows with cubs will wander up into Katmai’s mountains near the end of October and early November. In another two weeks or so the “teenage” subadults will follow, applying essential skills learned from their mothers – knowing when and where to den. Trudging last, with bellies bulging and nearly scraping the ground, bulky boars make their gradual ascent up tundra-carpeted and alder-filled mountain sides.
Some of Brooks Camp’s local denning areas are on the slopes of Dumpling Mountain, Mount La Gorce, Mount Katolinat, and Mount Kelez. If one were to have taken the Dumpling Trail clear up to the summit of Mt. Dumpling earlier this season, they would have seen two small dens as observed by some of Katmai’s rangers. As each brown bear selects denning sites, they use their long claws and iconic hump of muscle to dig away moss, tundra, and earth. This forms a void large enough for their bodies to fit comfortably into, yet small enough to maintain warmth secured through the insulation provided by the coming snow. It would be unlikely the same den inhabited during the previous winter would be used again.
Unlike squirrels, brown bears do not fall into a deep sleep as they hibernate. Instead they transition into a state of dormancy; an energy-consuming to an energy-conserving change. Much like when laptops are put into sleep mode to save energy without completely shutting down, Katmai’s brown bears also go into “sleep mode”, but will blink their eyes, stand, walk, and even exit their dens only to come right back and continue hibernating. They usually do not consume any food or water throughout hibernation. Urinating and defecating are out of the question. Their internal organs begin to shut down, not completely, but just enough to save their energy. A brown bear’s temperature will drop from 98°F at peak activity to as low as 89°F. However, the real mind-blowing change takes place in their hearts, dropping from 98 beats per minute in the summer to 8 to 10 beats per minute while in hibernation. What a drop!
For now, we wave good-bye to Brooks Camp and Katmai’s brown bears, resting along the beach or hidden within the shoulder-high grasses along Brooks River, actively snorkeling and swinging big bear feet in the air as they dive for salmon carcasses floating along the river’s bottom. We leave them to their brown bear antics of late fall and winter, hoping to see each one again next year as the melody of songbirds and the warmth of the spring sun awakens the slumbering creatures of Katmai from their dens.
