One-Stomach Animals That Eat Grass Plants

Dietary adaptations allow animals to survive on available resources, exploiting plant or animal-based food sources. Herbivores, or plant-eating animals, have evolved to extract a large amount of nutrients from relatively poor foods, such as grass. Most grass-eating animals possess a four-chambered stomach that allows food to pass slowly through the digestive tract, prolonging the extraction of nutrients. However, certain species use a single stomach, offsetting the low nutrient content of their feed by consuming larger quantities.

  1. Giant Panda

    • Iconic and rare, the giant panda (Ailuropoda melanoleuca) is one of the most ancient species of bear, sometimes referred to as a living fossil. Known for its striking black and white coat, giant pandas live in the remote bamboo forests of central China. Subsisting primarily on bamboo, the largest grass species, pandas rely on huge quantities of food in order to survive, sometimes consuming more than 30 pounds of bamboo shoots in a day. Paradoxically, although pandas are classified as carnivores, bamboo comprises 99-percent of their diet. Evolutionary biologists do not understand why the shift was made to a plant-based diet when physiologically pandas are built to consume meat, having only one stomach. This shift to a low-nutrient diet may account for the scarcity of the species, by negatively impacting reproductive frequency and longevity.

    Red Panda

    • Found in the same range as the giant panda, the red panda (Ailurus fulgens) was long considered to be a close relative to its larger namesake, but recent genetic mapping shows that they are more closely related to raccoons than bears. Feeding primarily on bamboo, red pandas are unable to effectively digest the cellulose-rich leaves and so only consume the shoots and tender stalks. Like the giant panda, they need to eat large quantities in order to survive, sometimes eating one-third of their body weight in one day, processing this food through a single stomach and long intestinal tract.

    Rabbit

    • Rabbits belong to the family Leporidae, which includes eight genera and 21 species. They are herbivorous mammals that subsist largely on grass and other plant matter. In order to digest low-nutrient, high-fiber feed such as grass, rabbits rely on a complex process of double-feeding to extract nutrients. Once eaten, grass passes through their single stomach and is divided into two forms of feces: hard pellets and soft feces. The hard pellets contain insoluble fiber and undigested plant matter, whereas the soft feces is a partially digested and highly nutritious mucus-like mass that is promptly consumed after expulsion. This process maximizes nutrient absorption while lessening the overall quantity of food intake needed, according to Peter R. Cheeke, author of "Rabbit Feeding and Nutrition."

    Pika

    • Pikas (Ochotona) are small herbivorous mammals comprising over 30 species. Dwelling in the rocky grasslands of North America, Asia and Europe, pikas are dependent on grass to provide the majority of their diet. Due to their high metabolism, they feed constantly through the summer while harvesting and drying grass for their winter stores. Like rabbits, who are a close relative, pikas double digest their food through a single stomach in order to extract the most nutrients. Although they differ from rabbits by only producing one type of feces, it is promptly eaten and digested again.