The blue wildebeest, or gnu, is one of the most numerous large mammals on the African savanna. Their massive herds, sometimes numbering over a million animals, are a defining feature of ecosystems like the Serengeti-Mara. Their specialized diet and pursuit of specific food resources are the sole driving force behind the famous Great Migration.
The Primary Food Source: Graminoids
Wildebeest are classified as obligate grazers, meaning their diet consists almost entirely of grasses, also known as graminoids. They prefer short, green, and highly nutritious grasses, avoiding tall, dry, and fibrous stalks. This selective grazing is driven by their need for high-quality forage intake to meet substantial energy needs.
Their specialized anatomy is that of a ruminant, featuring a large four-chambered stomach. The largest chamber, the rumen, hosts symbiotic bacteria and microorganisms. These microbes rapidly ferment and break down the tough cellulose in plant cell walls, allowing the wildebeest to extract nutrients efficiently.
The digestive system is optimized for processing tender, high-protein plant material. Wildebeest must constantly seek out the most palatable and digestible parts of the grass sward. This dependence on quality forage limits their ability to subsist on the coarse, low-nutrient grasses that other herbivores can tolerate.
Grazing Strategy and Behavior
The physical structure of the wildebeest’s mouth is adapted for its feeding style. They possess a wide, straight muzzle that allows them to crop large swaths of short grass close to the ground with each bite, enabling rapid consumption.
The grazing strategy involves rapid, almost continuous feeding, which is necessary to fill the large rumen. Wildebeest spend a significant portion of their day actively grazing, particularly during the cooler morning and late afternoon hours. This constant movement ensures that the herd does not linger long enough in one spot to deplete the preferred short grasses entirely.
The sheer number of animals in the migratory herds influences grazing efficiency, acting as a massive disturbance that stimulates new growth. As the herd moves, it quickly reduces the standing biomass of grass, creating a uniform, heavily cropped area. This behavior minimizes the risk of predation, as the collective vigilance of thousands of animals offers protection.
Seasonal Shifts and Water Dependence
The diet and movement of the wildebeest are governed by the availability of rain, which dictates where high-quality grass can be found. During the wet season, the animals disperse across the plains, feasting on abundant, newly sprouted grass rich in protein and moisture. This period is timed for calving, as the nutritious forage supports the high energy demands of reproduction.
As the dry season approaches and the rains cease, the quality of the standing grass declines. The remaining forage becomes coarse, dry, and low in nutritional content, forcing the herds to begin their migratory journey. The migration is a continuous search for areas that have received recent rainfall and can offer fresh, green grazing.
Wildebeest are highly dependent on drinking water, unlike some other savanna herbivores that can survive longer on moisture from plants. They are obligate drinkers, requiring access to fresh water sources at least every second or third day. This high water requirement means their feeding range is constrained by proximity to rivers or watering holes, which shapes the route and timing of the migration.
Ecological Role: Complementary Grazing
The feeding habits of the wildebeest are central to grazing succession, which benefits other savanna herbivores. While wildebeest are selective for short, highly nutritious leaf blades, they often graze alongside species like zebra and gazelle. The zebra, possessing a less selective digestive system, tends to arrive first and consumes the taller, tougher, and less nutritious upper parts of the grass stalks.
By removing this coarse material, the zebra lowers the height of the sward and exposes the leafier, more palatable parts that the wildebeest prefers. This interaction allows both species to utilize the same area without direct competition. The two species demonstrate niche differentiation, where their differing dietary preferences allow them to coexist and maximize resource use.
After the wildebeest have passed through and cropped the grass short, the resulting landscape is ready for the smaller Thomson’s gazelle. The heavy grazing pressure stimulates the growth of new, short shoots and exposes low-lying herbs and forbs. These tiny, protein-rich plants are the preferred food source for the gazelle, making the wildebeest diet a regulator for the entire grazing community.