The mantled howler is one of the largest Central American monkeys, and males can weigh up to 9.8 kg (22 lb).

It is the only Central American monkey that eats large quantities of leaves; it has several adaptations to this folivorous diet.

Since leaves are difficult to digest and provide less energy than most foods, the mantled howler spends the majority of each day resting and sleeping.

Howling allows the monkeys to locate each other without expending energy on moving or risking physical confrontation.

Its molars have high shearing crests, to help it eat the leaves,[12] and males have an enlarged hyoid bone near the vocal cords.

[13] Higher-ranking animals get preference for food and resting sites, and the alpha male gets primary mating rights.

[12][19] Mantled howler monkeys possess large salivary glands that help break down the leaf tannins by binding the polymers before the food bolus reaches the gut.

[13] The fact that the mantled howler relies so heavily on a low energy food source drives much of its behaviour – for example, howling to locate other groups and spending a large portion of the day resting.

[12] The leaves and fruit from Ficus trees tend to be the preferred source of the mantled howler.

[9] Movement within the rainforest canopy and floor includes quadrupedalism (walking and running on supports), bridging (crossing gaps by stretching), and climbing.

[13] The mantled howler uses a wide range of other sounds, including barks, grunts, woofs, cackles and screeches.

[20] Genital displays are used to indicate emotional states, and group members shake branches, which is apparently a playful activity.

However, in 1997 a Venezuelan red howler (Alouatta seniculus) was reported to use a stick as a club to hit a Linnaeus's two-toed sloth, (Choloepus didactylus), that was resting in its tree.

[30] The copulatory sequence begins when a receptive female approaches a male and engages in rhythmic tongue flicking.

The male responds with the same tongue movements before the female turns while elevating her rump, which allows for mating to begin.

[20] Adult females typically give birth every 19 to 23 months, assuming the prior infant survived to weaning.

[13] Natal emigration is performed by both sexes, with 79% of all males and 96% of the females leaving their original social group.

[7] The mantled howler is native to Colombia, Costa Rica, Ecuador, Guatemala, Honduras, Mexico, Nicaragua, Panama and Peru.

[5] Within Honduras, Nicaragua, Costa Rica and Panama, the mantled howler is found in locations throughout the countries.

[5] In Guatemala, the mantled howler is found through the central part of the country, and into southeastern Mexico south of the Yucatán Peninsula.

[5] The mantled howler is among the most commonly seen and heard primates in many Central American national parks, including Manuel Antonio, Corcovado, Monteverde and Soberania.

[3] Its numbers are adversely affected by rainforest fragmentation which has caused forced relocation of groups to less habitable regions, as well as deforestation and capture for the pet trade.

[3] In 2011, the primatologist Joaquim Veà Baró studied in Los Tuxtlas Biosphere Reserve in Veracruz, Mexico, the impact due to the fragmentation of populations and identified an increase in stress, especially among females, when a male from outside the group approached the area, because they felt that their offspring are being threatened.

Veà highlighted that "although this situation revealed up to what point individuals have the capacity for adaption, in some cases, undernourishment can lead to health problems that would make the population inviable".

Results can be compared to humans who "do not always eat everything which they should, for example in underdeveloped countries that have problems with malnutrition, rickets, a range of illnesses, but this does not put an end to the population, but rather provokes them to change their characteristics".

[37] However, the mantled howler can adapt to forest fragmentation better than other species due to its low energy lifestyle, small home ranges and ability to exploit widely available food sources.

[13] Dung beetles, which are also seed dispersers as well as nutrient recyclers, also appear to be dependent on the presence of the mantled howler.