Howler monkeys are very sociable and live in groups of 5-40 animals, led by a dominant older male, with several adults and sub-adults in attendance in the larger troops. The dominant male leads the troop's search for food in the forest canopy. They move very slowly, covering only about 400m per day. Howler monkeys are most active in the morning and evening, spending the middle of the day resting and the night asleep in the trees.
From dawn through till dusk, the roars of the howler monkey may be heard reverberating through the forest. The roars can be heard over 3km in the forest and 5km in the open, and are reputed to be the loudest sounds made by any land animal. The roars are made by air which is forced through a special bone in the monkey's throat (the hyoid bone), which amplifies the sound. The calls are thought to announce the presence of a troop to any other troops in the area. This avoids confrontation between groups, which would waste valuable energy. It also spaces troops throughout the forest, meaning that there is less competition between troops for food.
Threats to the red howler monkey: Although it is not an endangered species, it is threatened by the continued destruction of the South American rainforests.