Howler Monkey

The howler monkey is a term used to define the new world monkey. The etymology can be attributed to the fact these monkeys produce a shrill noise that resembles the howling sound. The new world is the term used to describe most of the western hemisphere of the earth, the term is specifically used to describe the American landscapes. Howler monkeys are primarily found in Central America and South America. An important point to notice is that this term is used to define the monkeys that belong to the genus Alouatta, it is not a scientific term that is used in the taxonomic classification. The howler monkey is also sometimes referred to as howlers. 

The brown howler and black howler are the most commonly found species of the howler monkey. Although all the howler monkeys belong to a single genus called Alouatta, various species are categorized into the genus. All the species discovered thus far are termed howler monkeys, the example of species that are considered as howlers includes the following, Alouatta arctoidea, Alouatta belzebul, Alouatta caraya, Alouatta coibensis, Alouatta discolor, Alouatta guariba, and Alouatta juara. Apart from these species, some other species are defined as howlers that belong to the same genus.

An important question that arises here is what is the unique feature of these animals that renders them such an important animal to be studied. The reason for this enormous fascination can be attributed to the fact that these animals are among the largest monkeys that are living on this planet. The body of a howler monkey can be 16 to 18 inches long, an important point here to note is that this length does not include the length of the tail. The tail of a howler monkey can grow up to 50 to 75 cm long, which when converted into inches is about 20 to 30 inches long. The long tail and the howling sound produced by these animals are some of the most important characteristic features of the howlers.

The article discusses the general characteristics and description of the howler. The article also focuses on the morphological characteristics, taxonomical classification, the diet and habitat of the animal. The article also briefly describes the social behaviour of the animal. The red howler monkey and the black howler are also briefly described in the article.

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General Description of Howler Monkey

Howler monkey as the name suggests is the term that shows annotation with the howling sounds, the monkey is aptly named after its ability to produce cacophonous cries. Howlers are primarily found in the American continent, the species diversity is highest in Central America and South America. The cacophonous cries are a way to establish their territory, it is believed that when the male members of the group produce such howling noises it is done primarily to announce the territory. The vocal cords of these monkeys are strong and are evolutionarily adapted to produce such sounds. Apart from the howling sounds they are also known for their body size, a unique feature is the presence of a long tail usually larger than the body. This feature is common in all species of howling monkeys.  Some of the commonly known species are black howler and red howler monkeys. The scientific name of these two species is Alouatta caraya and Alouatta seniculus respectively.

Howler monkeys are categorized as folivorous animals. The term is used to define the animals that are largely dependent on plant parts as a part of their diet especially the leaves of the trees, since they are considered as folivorous, the selection of the best leaves and fruits is hugely important for their survival. 

Taxonomical Classification

The taxonomic classification can be defined as a system of classification in which the organism is categorized based on its relative similarity with the other animal. The taxonomic classification is done to provide an understanding of the evolutionary history of the organism. It is also done to provide the links between the phylogenetic relationship. Lastly, taxonomy is used to study the common characteristics that are unique to the species. The taxonomic classification of howler monkeys is as follows, but before understanding the classification system it is important to note that the term howler monkey is used to describe different species of the howler monkeys like black howler (Alouatta caraya) and the taxonomic classification mentioned here describes the general classification system of the genus Alouatta.

Howler monkeys are classified under the kingdom called Animalia, this kingdom consists of all the organisms that require organic nutrients to sustain their life. The multicellular eukaryotic organisms are primarily considered as an animal in this kingdom. The kingdom is further classified as a phylum, the howler monkeys are categorized into a phylum called Chordata. 

The unique feature of this phylum is that the member of this phylum consists of a notochord during any stage of their life cycle. The phylum is characterized by the presence of the 5 synapomorphies, which include a notochord, dorsal hollow nerve cord, endostyle or thyroid, pharyngeal slits, and a post-anal tail. All these 5 features are well developed in every species of howler monkeys, thus categorizing them on the Chorda phylum.

The phylum is further divided into classes, howlers belong to the class called Mammalia. The characteristic feature of this class is the ability to produce progeny. The members of this class are majorly viviparous, another important feature to note is that the female members are characterized by the presence of mammary glands, these glands are used for lactation during the early developmental stage of progeny. This also signifies that the members of this phylum provide parental care. The howler monkey satisfies all the requirements of the phylum, they are viviparous animals that give birth to the progeny and provide parental care. The female of all the species of the howlers is known to have two mammary glands to support the life of young ones.

The class can be further classified as the order, howlers belong to the order called Primates. The term primates can be misleading, but it actually refers to the pre-developed ancestors of humans. The order is also defined as eutherian mammals constituting the taxonomic order. The characteristic features that are common to the howler monkey, as well as the order, constitute the following: they have large brains, visual acuity, colour vision, a shoulder girdle allowing a large degree of movement in the shoulder joint, and dexterous hands. A very interesting fact about the howler vision is that they have the three-colour vision, which is found in humans. The primates are known for adapting to living in challenging environments like a tropical forest, this holds for the howlers as well as they are primarily inhabitants of the forest.

Howler monkeys are further classified in a suborder called Haplorhini. The suborder is known for its dry-nosed members. The suborder contains tarsiers and the simians. Simians are the high primates the howler monkey along with other new world monkeys are classified into this infraorder.

They are further classified into the family called Atelidae. This family is among one of the five families that contain all the species of the new world monkeys. Apart from howler monkeys, other categories of monkeys are spider, woolly, and woolly spider monkeys. The family is further classified into genus, howler monkey belongs to the genus called, Alouatta. Under this genera various species are classified, some of the examples of the species are

• Alouatta arctoidea, 

• Alouatta belzebul,

•  Alouatta caraya,

•  Alouatta coibensis, 

• Alouatta discolor

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Morphological Features

The howler monkeys are of medium size, an interesting fact about them is the tail of a howler monkey is approximately five times larger than the body. The size of an adult howler monkey is larger than any monkey.  The size of the head and body ranges from about  22 to 36 inches, since the tail is the longest part of the body, the average size of the tail among different species is 23 to 36 inches. The tail is considered the most important organ of the body, it is used to hang and clutch the branches of trees.

A characteristic feature of these animals is the presence of short snouts and wide and round nostrils. The side-opening nostrils and no pads on their rumps. Another unique feature is the dextrous hand of the animal.

Howler monkeys are also known to have bearded structures and long thick hair that covers the entire body including the tail. Based on the colour of the hair the howlers are classified as red howler monkey or black howler monkey. Howler monkeys are commonly found in red, black, and brown but the red coloured howler known as the red howler monkey (Alouatta seniculus) is the most common.

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Behavioural Traits

The howler monkey irrespective of their species are considered calm and peaceful animals, they are generally not seen attacking any human or animal. Although the howling sound produced by them is very loud, it is used to communicate and mark territory among the different groups. The howlers are social animals, they live in groups and the groups follow a social hierarchy.

The group of a howler is known as a troupe, it contains about 12 to 15 adult males and females. The group is led by an alpha male. The alpha is generally aged and is determined by its physical strength. An interesting trend that is seen in this troupe is the exclusion of young male and female members of the troupe upon reaching sexual maturity. Upon leaving the group, they live solitary until another troupe is willing to accept the member, this behavioural trait is very unique among the howlers.  

As discussed earlier the troupe is led by a dominant male but there is the presence of dominant females, the primary role of these females is to maintain the social hierarchy. An interesting point about these animals is that although they have a large body and were thought to be aggressive unlike their relative family members, they are considered the laziest monkey on the planet. It is estimated that they spend almost 80% of their life sleeping. Although they spend most of the time resting, they are considered diurnal animals as the maximum activity is seen during the day.

Reproduction

Howler monkeys are categorized as primates, which is one of the most evolved orders. Since they are highly evolved and anatomically developed they undergo sexual reproduction. The fertilization process is internal, that is the fusion of male and female gametes that takes place inside the reproductive tract of females.

They mate within the troupe, they are generally seen as polygamous animals. Sexual maturity is attained at the age of four. Females conceive their first offspring at this age, the gestation period can last up to six months. They are not seasonal breeders, they mate throughout the year. A single mate produces a single offspring, and a female produces one offspring every 2 to 3 years. 

Since the number of progeny is low, the parental care provided to the offspring is very high. Howler monkeys including all the species like red howler or black howler monkey are considered mammals, that is the female parent provides lactation by the mammary gland to sustain the life of the baby howler. One of the interesting baby howler monkey facts is that despite the high parental care provided during early developmental years, they are forced to leave the trope and find a different troupe.

Diet 

Howler monkeys are folivorous animals, they are mainly dependent on the plant leaves as their diet. They are also seen eating fruits. It can be said that fruits and leaves are the primary sources of their food. Apart from the folivorous nature of their diet, they are seen eating chicken eggs, such cases are reported in the troupes living near the human settlements.

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Habitat

Howler monkeys are tropical animals, almost every species of the monkey is found living in tropical habitats. Central America and South America are the two major geographical locations where high species diversity of howler are found. They are also found in tropical Mexico. The habitat of these primates includes tropical rainforest, tropical dry forests and cloud forests. 

Threats and Life Span

The life span of different species of howler monkeys may vary but in general, they live about 10 to 25 years, they are not easily susceptible to disease but they are sometimes seen affected by toxin poisoning. It is caused by the ingestion of plant toxins in high concentrations during feeding. Apart from it, they have a very low number of natural predators. Some of the predators are jaguars, snakes, and birds.

Although howlers are not under the threatened list of IUCN, some subspecies are considered endangered. An example of such subspecies is the Maranhao red-handed howler of Brazil and the Yucatan black howler of Guatemala. The greatest risk of the howler population is by humans. Constant deforestation has lead to habitat loss and habitat fragmentation, which has greatly impacted the overall lifestyle of these primates. They are also subjected to live in captivity for commercial exploitation thus leading to the shortened life span of the animal.

Summary at a Glance

• Howler monkey belongs to the genus Alouatta.

• The most common species is the red howler monkey

• They are arboreal animals, the most distinctive feature is the howling sound.

• They are considered folivorous animals.

• They are found in tropical forests.

• The body is covered with hair and the tail is almost five times the size of the body.

• The average weight of the animal is 3-9 kg.

• The average life span is 15 to 20 year

• Natural predators of the primate are jaguars, snakes and some birds.

• Endangered subspecies are Maranhao red-handed howler of Brazil and Yucatan black howler of Guatemala.