The pronghorn (Antilocapra americana), a species exclusive to North America, is often incorrectly referred to as an antelope, yet it is the sole surviving member of its own evolutionary family. This mammal is the fastest land animal on the continent, relying on speed to thrive in the harsh, open, semi-arid environments of the Great Plains, sagebrush steppe, and desert grasslands. Its ability to survive in these nutrient-scarce landscapes is tied to a highly selective and adaptable diet. The pronghorn seeks out the most nutritious plants available, making its foraging habits highly specialized.
Shrubs and Forbs: The Staple Diet
Pronghorns are classified primarily as browsers, distinguishing them from grazers like cattle or bison that consume mostly grasses. Their diet is dominated by forbs (broad-leafed flowering plants) and woody shrubs. Forbs are particularly sought after because they contain a higher concentration of protein and lower levels of fiber compared to grasses, providing a substantial nutritional return.
Forbs often contribute the largest portion of the pronghorn’s diet, sometimes accounting for over 50 to 60 percent of consumption. Specific forb examples include cushion buckwheat (Eriogonum ovalifolium) and prostrate knotweed (Polygonum aviculare), which are highly selected for their nutritional density. Pronghorns can consume a multitude of plant species, with some analyses detecting as many as 137 different species in their diet across various seasons.
Shrubs form the secondary but equally important component of their forage base. Wyoming big sagebrush (Artemisia tridentata), bitterbrush (Purshia tridentata), and rabbitbrush (Chrysothamnus spp.) are commonly consumed woody species. This dependence on shrubs is pronounced in sagebrush ecosystems, where these plants offer consistent nutrition when other forage is unavailable. The pronghorn’s small stomach size favors a diet of concentrated nutrients, which woody browse and forbs provide.
Seasonal Changes in Consumption
The proportion of shrubs and forbs consumed shifts significantly throughout the year, driven by plant availability and the pronghorn’s changing nutritional needs. During the spring and early summer, the diet leans heavily toward forbs. This consumption pattern is crucial because the high protein content of newly sprouted forbs supports the energy demands of late gestation and early lactation for female pronghorns.
As the hot, dry periods of summer arrive, forbs in arid regions begin to lose their moisture and nutritional quality. During this time, the pronghorn’s forage selection may transition to more browse, or they may travel widely to find forbs that remain succulent. An extended greening-up period allows forbs to serve as a significant source of water, reducing the pronghorn’s reliance on open water sources.
In winter, the diet can become almost entirely dependent on evergreen shrubs, especially in northern habitats where snow covers ground vegetation. Sagebrush is an important winter food, as it often remains accessible on wind-blown ridges and offers relatively higher protein content than dormant grasses. This seasonal switching allows pronghorns to continually optimize their nutrient intake from the available, highest-quality species.
Specialized Digestion and Tolerance
The pronghorn is a ruminant, possessing a four-chambered stomach, a digestive system shared with cattle and deer. However, its digestive process is uniquely adapted to handle plant compounds that are toxic or repellent to many other grazing and browsing animals. This adaptation allows the pronghorn to exploit the abundance of chemically defended plants in its habitat.
Many of the preferred shrubs, such as sagebrush, contain high concentrations of plant secondary compounds (PSC), including terpenes and phenols, which serve as chemical defenses. These compounds can be toxic to livestock and other ungulates if consumed in large quantities. The pronghorn manages this challenge through a combination of highly selective feeding and an enhanced detoxification system.
The pronghorn limits its intake of any single plant species, a behavior known as diet mixing, which prevents it from consuming a toxic dose of any specific compound. Its specialized gut microbes play a role in breaking down and detoxifying these chemical compounds within the rumen. This biological mechanism allows the pronghorn to gain nutrients from plants that others cannot utilize, acquiring benefits such as antioxidants from the compounds.