Nuts, seeds, fruits and flowers are important supplements to the howler monkey's diet, 40% of which is made up of green leaves. It has a specially enlarged intestine filled with strong bacteria which help it to digest large amounts of its tough, fibrous food. The howler monkey chooses young tender leaves, together with older ones which contain more nourishment. It can live on leaves alone for several weeks by moving slowly to conserve energy and by feeding selectively. Small animals may also be eaten if they are caught by the monkeys.