The dinner bell is ringing high in the Mission Mountains, and grizzly bears are heeding the call.
Every year in July, cutworm moths migrate from the plains toward the alpine highlands of the Mission Mountains, where the moths feed on late-blooming alpine wildflowers. Grizzly bears follow. The moths provide grizzlies with the highest source of protein available - even higher than feeding on deer.
The Confederated Salish and Kootenai Tribes have closed about 10,000 acres in the Mission Mountains Tribal Wilderness to let the grizzlies feed without human interruption.
McDonald Peak and the surrounding areas in the Mission Mountains Tribal Wilderness closed July 15 and will remain closed until Oct. 1.
Grizzly bears have historically gathered in this area to feed on army cutworm moths that concentrate in the areas during July, August and September.
Grizzlies also feed on the moths in Glacier National Park, though the Park only closes areas if the bears are close to campgrounds or trails on an as-needed basis.
The closure allows many bears to remain at high elevations longer each year and gain additional weight, which tribal spokesperson Germaine White said may result in fewer human confrontations when the grizzly bears go to lower elevations in the fall.
The moths arrive each year at the onset of the flowering season for the alpine flower communities, near the end of June and the first part of July. The moths feed at night on the nectar of several flowers, including green bluebell, thick-leaved groundsel, mules-ears and elephant's head.
During the day, moths aggregated under the various rock formations, to seek shelter while metabolizing nectar. According to researcher Kate Kendall, the moths cluster throughout the talus and boulder fields.
Moth samples collected in late August were found to contain approximately 72 percent fat, 28 percent protein, and less than 1 percent carbohydrate. The high fat content produced a relatively high gross energy for moths in late summer compared to other available bear foods, according to research from Yellowstone National Park.
Both sexes of army cutworm moths return to the plains in the fall where adult females lay their eggs. Females returning to the plains in the fall had mature eggs and researchers concluded they mated sometime prior to their arrival. Based upon scientific observations of moths copulating at nectar feeding sites and at daytime aggregation sites, they found that a significant amount of reproductive behavior occurs during their alpine stay in the Mission Mountains.
The rise in fat content not only provides energy needed for fall migration back to the plains, but may also be important for sexual maturation and stimulating reproductive behavior, according to Kendall.
The army cutworm moth has been reported in North America for at least 200 years and was distributed from the Atlantic to the Rocky Mountains and from Canada to Texas. It was first noted to cause major crop damage in great numbers as early as 1743 in the New England area, and in 1861 caused massive crop damages in southern Illinois and Missouri.
But for grizzlies, the arrival of the moths signals a time to put on weight for the winter.