A monkey renowned for its loud call, which the males make to tell other groups where the troop is currently feeding. This helps them save energy by avoiding having to patrol a territory and conflicting with neighbours.

Statistics
Females 48-57cm with a 52-68cm long tail and weighing 4.2-7kg. Males 51-63cm with a 57-68cm long tail and weighing 5.4-9kg.

Physical description
A monkey with a prehensile tail and medium length orange-brown fur (sparser and paler on the belly). Males have a paler beard.

Distribution
From northern Colombia and Venezuela south to the Amazon, and south of the Amazon from the Andes to Rio Madeira and as far south as southern Bolivia.

Habitat
Forests of all types.

Diet
Leaves and fruit, quite a lot of it unripe, and often swallowing soil.

Behaviour
Howler monkeys usually live in groups of 4-11 individuals, with one or more males. They are active in the daytime, usually preferring the lower to middle canopy of the forest, and descending to the understorey and ground to feed. Over half their waking hours are spent resting, saving energy on their low-sugar diet. Division of labour also helps, with males defending the troop and settling disputes whilst females concentrate on reproduction. There is no defended territory, and neighbouring troops range over overlapping areas.

Reproduction
Breeding can take place at any time of year, with one youngster (rarely twins) being born after a gestation of 180-194 days. The female will not give birth again for 1-2 years. Once independent, both male and female youngsters leave their mother's group, which is unusual.

Conservation status
Not currently threatened.

Voice
Howler monkeys are named for the very loud roaring sound the males make that allows communication between neighbouring groups. One of the loudest sounds made by any animal, the call can travel over 1.6km. Howling occurs in the mornings and each time the troop moves to a new feeding site, allowing neighbouring troops to know where they are and avoiding energy-wasting conflicts.