The moose (Alces alces), the largest member of the deer family, inhabits the boreal and mixed deciduous forests of the Northern Hemisphere. During the summer, a moose consumes 40 to 60 pounds of highly nutritious aquatic and terrestrial plants daily to build up body fat reserves. The arrival of winter forces a dramatic shift in diet as most vegetation dies back, is covered by snow, or becomes dormant and nutrient-poor. The primary challenge is acquiring enough calories and protein from the woody, high-fiber material available to survive until spring.
Essential Winter Browse
The winter diet of the moose is almost entirely composed of woody browse, consisting of the twigs, buds, and bark of deciduous and coniferous trees and shrubs. This shift is necessary because the soft, leafy forage of summer is unavailable. Although moose naturally seek out nutrient-dense plant parts, severe winter conditions limit this selection.
Key deciduous species, such as willow, aspen, paper birch, and red-osier dogwood, are preferred for their higher nutritional content, even when dormant. Willow twigs are often the most popular food source, accessible because the animal’s height allows it to reach up to eight feet. However, these preferred species are often not abundant enough to sustain the moose throughout the entire winter.
When preferred deciduous browse is depleted, moose rely on maintenance browse, which is less palatable but provides necessary bulk. Coniferous species, particularly balsam fir, subalpine fir, and eastern hemlock, become important dietary components in late winter. Moose also strip bark, especially from trees like aspen and birch. The Algonquin name for the animal, “moosu,” translates to “bark stripper,” reflecting this distinctive behavior. An adult moose may consume 11 to 18 kilograms of twigs per day.
Digestive Adaptations for Low-Quality Diet
To process the tough, woody browse of winter, the moose relies on its specialized digestive system, classifying it as a ruminant. This system centers on a four-chambered stomach, where the largest chamber, the rumen, acts as a fermentation vat. While the moose is adapted to a low-fiber diet in summer, it must process high-fiber wood during winter.
Within the rumen, specialized microorganisms, including bacteria and protozoa, break down the fibrous material. These microbes are essential for digesting cellulose and hemicellulose, the structural carbohydrates in woody stems. Lignin, however, is largely indigestible to the moose and its microbes.
The digestive process slows down significantly in winter compared to summer. This prolonged retention time allows for maximum extraction of nutrients from the low-quality forage. This physiological ability to process the high-lignin, low-calorie diet is coupled with a seasonal reduction in metabolic rate, helping the moose survive the nutritional deficit.
Energy Conservation and Foraging Strategy
Survival in winter requires balancing calorie acquisition with minimizing energy expenditure. Moose employ several behavioral strategies to conserve energy. Their large size and long legs allow them to navigate snow depths that would immobilize smaller deer species, but deep snow remains an obstacle.
When snow depths exceed about 90 centimeters, movement becomes restricted, limiting forage access and increasing energy costs. To mitigate this, moose often engage in “yarding,” concentrating activity in sheltered areas. These are typically dense stands of conifers, which offer protection from wind and snow, providing thermal cover and reducing travel distance to available food.
The foraging strategy maximizes caloric return for minimal effort, leading to reduced overall activity levels. Instead of roaming widely, moose repeatedly browse the same patches of palatable shrubs. They also strip bark from larger trees for a consistent food source and use their height to browse the higher branches of small trees, reaching food inaccessible to other species.