The mountain goat (Oreamnos americanus) is a large, hoofed mammal native to North America’s extreme mountain environments. These ungulates inhabit the rugged, steep alpine and subalpine zones, primarily across the western cordillera. Surviving in this harsh, high-altitude habitat requires a specialized diet and robust physiological adaptations. As herbivores, mountain goats rely entirely on the available, often sparse, vegetation of their rocky domain. Their digestive system is finely tuned to extract maximum nutrition from the tough, fibrous plants found above the treeline.
The Core Diet of Alpine Vegetation
The bulk of a mountain goat’s caloric intake during the growing season is derived from a variety of alpine plants. Their diet includes numerous species of grasses (Poaceae) common in mountain meadows, and sedges (Cyperaceae). They also consume various forbs, which are flowering herbaceous plants that offer a burst of nutrients when in bloom.
Mountain goats browse on the leaves and tender shoots of low-growing shrubs and dwarf willows when available. Mosses and lichens can also contribute a small portion of their diet. The physical composition of these alpine plants is often tough and highly fibrous due to the short, intense growing season.
The ability to process this challenging vegetation stems from the mountain goat’s classification as a ruminant. Like cattle and deer, they possess a complex four-chambered stomach, an adaptation for digesting cellulose. The first two compartments, the rumen and reticulum, act as large fermentation vats where specialized microbes break down the plant matter.
This microbial action allows the goat to efficiently process the structural carbohydrates found in the cell walls of alpine plants. The process involves regurgitating and re-chewing the food, known as “chewing the cud,” which further breaks down the tough material. This mechanism ensures the mountain goat can extract sufficient energy and protein from a diet indigestible for many other mammals.
Adapting to Seasonal Food Scarcity
The mountain goat’s dietary composition shifts dramatically between warmer and colder months to ensure survival. During the summer, the abundance of fresh, lush growth allows the goats to consume a high-quality diet rich in protein and nutrients. They spend this period intensively foraging on new growth to build fat reserves necessary for surviving the lean winter.
As winter arrives, preferred forage becomes dormant and is often buried under snow. Their diet shifts to less nutritious, tougher materials, such as dried grasses they must paw through snow to reach, bark, twigs, and coniferous needles. The protein concentration in their food can drop significantly, sometimes falling below the levels needed for maintenance.
To cope with scarcity, the goats adopt a strategy of energy conservation. They limit movement, often remaining on wind-scoured ridges where some forage is exposed, to minimize energy expenditure. The lower nutritional value of their winter diet, combined with the energy cost of maintaining body temperature, can lead to a loss of up to 27% of their body weight over the season.
Critical Mineral and Water Consumption
Beyond the vegetative matter that supplies energy, mountain goats require specific non-vegetative elements, particularly sodium, which is often lacking in alpine environments. The primary method for obtaining these necessary micronutrients is geophagy, the intentional consumption of earth or soil. They seek out natural mineral licks, which are sites where deposits of salt and other minerals are exposed.
The consumption of mineral-rich soil helps supplement their intake of sodium, calcium, and magnesium, which are needed for metabolic function and bone development. Mountain goats travel considerable distances and face increased risk of predation to visit these licks, demonstrating the importance of this resource. The impulse to visit these sites is strongest in late spring and early summer when the demands of lactation and new growth are highest.
Acquiring sufficient water is a challenge in their high-altitude environment, where open liquid water can be scarce or frozen for much of the year. Mountain goats often meet hydration needs by consuming the moisture-rich plants they eat during the summer. In the winter, they rely almost entirely on eating snow and ice to fulfill daily water requirements. This allows them to remain in steep, high-elevation refuges without needing to descend to lower, more hazardous water sources.