Herbivores are animals that primarily consume plants and plant-based materials. Their diet mainly consists of leaves, fruits, flowers, seeds, and stems. Some common examples of herbivores include cows, sheep, deer, rabbits, and elephants. Many herbivores have evolved specialized digestive systems that allow them to effectively break down cellulose found in plant cell walls. Some, like cows, practice rumination, where they regurgitate and chew their food to aid in digestion. A herbivorous diet can vary greatly depending on the availability of plants in their habitat and seasonality of certain food sources.