Brown Howler Monkey (Alouatta guariba)

Brown Howler

The Brown Howler Monkey, scientifically known as Alouatta guariba, is a fascinating species of New World monkey native to South America. These primates are known for their loud and distinctive howls, which can be heard up to three miles away and are believed to be the loudest of any land-based animal.

Brown Howler Monkey

The Brown Howler Monkey is an arboreal species that can be found in the canopy of tropical and subtropical forests, where they spend most of their time moving from one tree to another in search of food.

In this post, we will explore the fascinating world of the Brown Howler Monkey, including its physical characteristics, behavior, habitat, diet, and conservation status. Whether you are a nature enthusiast or simply curious about these amazing creatures, this post will give you a deeper understanding of one of the most fascinating primates in the world.

The Brown Howler Monkey was previously known by the scientific name of Alouatta fusca. In 1996 this was changed to Alouatta guariba. They are endemic to Brazil.

Physical characteristics

They have a brown coat hence the name, but this can vary slightly from a reddish-brown through to a near black-brown color. The male Brown Howler Monkeys range from about 55 to 60 cm in length, with their tail another 50 to 70 cm in length. The females are slightly smaller, 45 to 50 cm in length, with tails of 50 to 60 cm. The male howler monkey weighs anywhere between 5 to 8 kgs, and the females between 4 and 5 kgs.

The Brown Howler Monkey is known hence its name, by the terrific howl which can be heard over a mile away. It is thought that they use their howls to express their presence and claim their right to a territory for food. Their amazing prehensile tails also allow them to hang from trees.

These primates have a specialized enlarged hyoid bone in their throats, which allows them to produce deep and resonant howls that can carry for long distances. These vocalizations serve multiple purposes, including territorial marking, communication with group members, and attracting mates. The haunting sounds of the Brown Howler Monkey can create a mystical atmosphere in the rainforest, captivating the attention of anyone fortunate enough to witness them in their natural habitat.

The Brown Howler Monkey is a threatened species, mostly due to habitat destruction by humans.

Another fascinating physical characteristic of the Brown Howler Monkey is its prehensile tail. This tail serves not only for balance but also acts as an extra limb, enabling them to navigate their arboreal habitat with exceptional dexterity. The tail possesses a specialized gripping ability, allowing the monkeys to tightly grasp branches and swing effortlessly from tree to tree. This adaptation is particularly advantageous in their search for food and their overall survival in the dense forest environment.

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The females give birth to usually one monkey, which is fully weened by one year of age. During this time, the males will aggressively protect their territory.


These remarkable creatures primarily inhabit dense forests, favoring areas with a high canopy cover and abundant vegetation. They are particularly well-suited to live in tropical and subtropical rainforests, where they can take advantage of the diverse food sources available.

Within their extensive range, Brown Howler Monkeys adapt to different types of habitats, including primary and secondary forests, as well as fragmented habitats. However, they tend to thrive best in undisturbed areas with minimal human encroachment.

Their presence in the Atlantic Forest, one of the world’s most biodiverse and endangered ecosystems, makes them an essential species for conservation efforts. The Brown Howler Monkey plays a crucial role in seed dispersal, contributing to the forest’s regeneration and overall ecosystem health.

Although they are predominantly arboreal, spending most of their lives in trees, Brown Howler Monkeys are relatively versatile and can adapt to various altitudes and vegetation types. From lowland forests to montane regions, they have managed to adapt and survive in diverse environments throughout their distribution.

Social structure and behavior

One notable aspect of their social organization is their preference for living in groups called troops. These troops typically consist of several males, females, and their offspring. The size of a troop can vary, but it is usually composed of around 8 to 15 members. Within the group, there is a clear hierarchy with dominant males leading the troop and defending their territory.

Communication plays a vital role in the social dynamics of the brown howler monkeys. They are renowned for their deep, resonant vocalizations that can be heard echoing through the forest. These vocalizations, often referred to as howls, serve multiple purposes, including marking territory, establishing contact between group members, and warding off potential threats. The low-frequency howls are so powerful that they can carry over long distances, ensuring effective communication within the troop.

Another interesting behavior of the brown howler monkey is their sedentary lifestyle. They are primarily arboreal creatures, spending most of their time in the upper canopy of trees. They move slowly and with great agility, using their prehensile tails to maintain balance while traversing branches. This arboreal habitat provides them with protection from predators and access to their primary food source – leaves.

Within the troop, cooperative behavior is observed, particularly when it comes to caring for the young. Females play a significant role in nurturing and raising the offspring, while males contribute to the protection of the group. This cooperative parenting helps ensure the survival and well-being of the next generation.

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Diet and feeding habits

The Brown Howler Monkey has a unique digestive system that allows them to efficiently extract nutrients from tough, fibrous leaves. They have a large, specialized stomach called a sacculated stomach, which helps with the fermentation process. This fermentation breaks down the cellulose found in leaves and enables the monkeys to extract nutrients from them.

In addition to leaves, these monkeys also consume fruits, flowers, and even some insects. However, leaves remain their main source of sustenance. They are known to be selective feeders, carefully choosing the leaves they consume based on their nutritional content. This selective feeding behavior helps them maximize their nutrient intake.

Reproduction and life cycle

The Brown Howler Monkey has a polygynous mating system, where dominant males mate with multiple females within their group. During the mating season, which typically occurs between April and June, the males compete for dominance through vocalizations and physical displays. Their deep, resonant howls can be heard echoing through the dense forests, signaling their territory and attracting potential mates.

After successful mating, the gestation period lasts approximately 180 to 190 days. Female howler monkeys give birth to a single offspring, known as an infant. The newborns are incredibly small and helpless, weighing only around 400 grams. They cling tightly to their mother’s abdomen, relying on her for protection and nourishment.

For the first few months, the infant remains close to its mother, relying on her for warmth, milk, and guidance. As it grows, the infant becomes more independent, gradually exploring its surroundings and learning essential skills such as climbing and foraging.

The Brown Howler Monkey experiences a slow life cycle compared to other primate species. The infants stay with their mothers for an extended period, typically up to two years, receiving crucial social and survival lessons. During this time, they gradually develop their own set of skills and knowledge, preparing them for adulthood.

Once the young howler monkeys reach sexual maturity, which happens around four to five years of age, they leave their natal group to find a new group or establish their own. This dispersal helps prevent inbreeding and promotes genetic diversity within the species.


We hope you enjoyed diving into the fascinating world of the Brown Howler Monkey, Alouatta guariba, with us. These incredible creatures, known for their unique vocalizations and distinctive appearance, are a significant part of the rich biodiversity found in the forests of South America. From their social dynamics to their feeding habits, we’ve explored various aspects of their lives and shed light on their conservation status. By understanding and appreciating these remarkable primates, we can work towards preserving their habitats and ensuring their survival for generations to come. Thank you for joining us on this exciting journey through the captivating world of the Brown Howler Monkey.

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