The howler monkey eats mostly leaves. They are folivores, which are animals that specialize in eating leaves, but they will also consume fruits, nuts and flowers as well as birds' eggs on occasion. Characteristics of folivores include having long digestive tracts so that leaves can be digested.
Since howler monkeys generally eat leaves, they frequently remain in branches high up in the tree tops, rarely descending to the ground. The leaves these monkeys consume provide most of their nutritional and water needs. Although howler monkeys prefer younger leaves, they consume mature leaves when necessary. Many howler monkeys will also feed on moss, buds, seeds and flowers to supplement their diet. A flexible diet has allowed the howler monkey to live in a wider range of habitats, unlike some other types of monkeys. This flexibility also means that the howler monkey is less likely to experience significant population losses.