Alouatta palliata trabeata

Mantled Howler

The Mantled Howler (Alouatta palliata), or sometimes the Golden-mantled Howling Monkey, is a species of howler monkey, a type of New World monkey, from Central and South America. It is one of the monkey species most often seen and heard in the wild in Central America. It takes its "mantled" name from the long guard hairs on its sides.

The Mantled Howler is one of the largest Central American monkeys, similar in size to Geoffroy's Spider Monkey, and males can weigh up to . It is the one Central American monkey whose diet is composed largely of leaves. The Mantled Howler has several adaptations to this folivorous diet. Since leaves are difficult to digest and provide less energy than most foods, Mantled Howlers spend the majority of each day resting and sleeping. Male Mantled Howlers also have an enlarged hyoid bone, which is a hollow bone near the vocal chords. This enlarged bone amplifies the calls made by the male, which give the monkey its common name of "howler". Howling allows the monkeys to locate each other without expending energy on moving or risking physical confrontation.

The Mantled Howler lives in groups that can have over 40 members, although usually have fewer. Most Mantled Howlers of both sexes are evicted from the group upon reaching sexual maturity, and so most group members are unrelated. The most dominant male, the alpha male, gets preference for food and resting places, and mates with most of the receptive females.

The Mantled Howler is important to the rainforest ecology as a seed disperser and germinator. Although it is impacted by deforestation, it appears to be able to adapt better than other species, due to its ability to feed on abundant leaves and its ability to live in a limited amount of space.

Physical description

The Mantled Howler's appearance is similar to other howler monkeys of the genus Alouatta except for coloration. The Mantled Howler is primarily black except for a fringe of gold to buff hair on each side that gives it its common name. When the males reach maturity, the scrotum turns white. Females are between , in body length and males are between . Its prehensile tail is between long. Adult females generally weigh between while males typically weigh between . Average body weights can vary significantly between monkey populations in different locations. The brain of an adult Mantled Howler is about .

The Mantled Howler shares several adaptations with other species of howler monkey that allow it to pursue a folivorous diet, that is a diet with a large component of leaves. Its molars have high shearing crests, to help it eat the leaves, and males have an enlarged hyoid bone near the vocal chords. This hyoid bone amplifies the male Mantled Howler's calls, allowing it to locate other males without expending much energy, which is important since leaves are a low energy food.

Geographic range

The Mantled Howler is native to Colombia, Costa Rica, Ecuador, Honduras, Guatemala, Mexico, Nicaragua and Panama. Its range covers most of Honduras, Nicaragua, Costa Rica and Panama. In Colombia and Ecuador, it is found in a narrow corridor bordered by the Pacific Ocean to the west and the Andes Mountains to the east. In Colombia it is also found in a small area near the Caribbean Sea close to the Panama border. In Guatemala, the Mantled Howler is found through the central part of the country, and then into southeastern Mexico south of the Yucatán Peninsula. 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. The Mantled Howler lives in several different types of forest, including secondary forest, semi-deciduous forest and riverine forest. Higher densities of Mantled Howlers appear to be found in older areas of forest and in areas containing evergreen forest.

Behaviour

Social structure

Group size ranges from 10 to 20 members, generally 1 to 3 adult males and 5 to 10 adult females. However, some groups have over 40 members. Males outrank females, and younger animals of each gender generally have a higher rank than older animals. Higher ranking animals get preference for food and resting sites, and the alpha male generally gets exclusive mating rights. Animals in the group are generally not related to each other as most members of both sexes leave the group before sexual maturity.

Grooming behaviour in the Mantled Howler has been shown to reflect social hierarchy, where dominant individuals groom subordinates. However, grooming activity is infrequent. Aggressive interactions between group members is not often observed either However, studies have shown that aggressive interactions among group members do occur, and are probably not often observed because these interactions tend to be quick and silent.

Mantled Howler groups that have been studied have occupied home ranges of between . Groups do not defend exclusive territories, but rather several groups have overlapping home ranges. However, if two groups meet each group will aggressively attempt to evict the other. On average, groups travel up to about each day.

The Mantled Howler has little interaction with other sympatric monkey species. However, interactions with the White-headed Capuchin occur. These are most often aggressive, with the smaller capuchins are more often the aggressors. However, affiliative associations between the capuchins and howlers do sometimes occur, mostly involving juveniles playing together. Other times the capuchins and howlers may feed in the same tree, apparently ignoring each other.

Diet

The Mantled Howler is the most folivorous species of Central American monkey. It relies on leaves for much of its diet. Leaves make up between almost 50% and 70% of the Mantled Howler's diet. The Mantled Howler is selective about the trees it eats from. It also prefers young leaves to mature leaves. This selectivity is likely to reduce the levels of toxins ingested, since certain leaves of different species contain toxin levels. Young leaves generally have less toxins as well as more nutrients than more mature leaves, and are also usually easier to digest. Leaves from Ficus trees tend to be preferred over other leaves. Although leaves are abundant, they are a low energy food source. 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.

Although leaves tend to make up the bulk of the Mantled Howler's diet, fruit can also make up a large portion of the diet. When available, the proportion of fruit in the diet can be as much as 50%, and can exceed the proportion of leaves. Figs tend to be a preferred fruit. Flowers can also make up a significant portion of the Mantled Howler's diet. Flowers are eaten in particularly significant quantities during the dry season.

The Mantled Howler tends to get the water it needs from its food, but it does sometimes drink from tree holes. It drinks from tree holes more during the wet season than during the dry season. It probably also drinks water from bromeliads.

Like other species of howler monkeys, almost all individual Mantled Howlers typically have full three color vision. This is different from other types of New World monkeys, where most individuals have two color vision. The three color vision exhibited by the Mantled Howler (and other howlers) is believed to be related to its dietary preferences.

Locomotion

The Mantled Howler is diurnal and arboreal. Movement within the rainforest canopy and floor includes quadrupedalism (walking, running, and galloping on supports), bridging (crossing gaps by stretching), and climbing. It will also sometimes leap to get to another limb.

However, the Mantled Howler is a relatively inactive monkey. It sleeps or rests the entire night and about three quarters of the day. Most of the active period is spent feeding, with only about 4% of the day spent on social interaction. This lethargy is an adaptation to its low energy diet. It uses its prehensile tail to grasp a branch when sleeping, resting or when feeding. It can support its entire body weight with the tail, but more often holds on by the tail and both feet. A study has shown that the Mantled Howler reuses travel routes to known feeding and resting sites, and appears to remember and use particular landmarks to help pick direct routes to its destination.

Communication

The Mantled Howler gets its name from the calls made by the males, particularly at dawn and dusk, as well as in response to disturbance. These calls are very loud and can be heard for several kilometers. The calls consist of grunts and repeated roars that can last for four to five seconds each. The volume is produced by the hyoid bone — a hollow bone near the vocal chords — amplifying the sound made by the vocal chords. Male Mantled Howlers have hyoid bones that are 25 times larger than similarly-sized spider monkeys, and this allows the bone to act like the body of a drum in amplifying the calls. Females also call but their calls are higher in pitch and not as loud. The ability to produce these loud roars is likely an energy saving device, consistent with the Mantled Howler's low energy diet. The roars allow the monkey to locate each other without moving around or risking physical confrontations.

The Mantled Howler utilises a wide range of other vocalisations. These include barks, grunts, woofs, cackles and screeches.

The Mantled Howler also uses non-vocal communication. It engages in "urine rubbing" when in a distressful social situation. This consists of rubbing the hands, feet, tail and/or chest with urine. Lip smacking and tongue movements are signals used by females to indicate a invitation to mate. Genital displays are used to indicate emotional states, and group members shake branches, which is apparently a playful activity.

The Mantled Howler is often indifferent to the presence of humans. However, when it is disturbed by people, it often express its irritation by urinating or defecating on them. It can accurately hit its observers despite being high in the trees.

Tool use

The Mantled Howler is not known to use tools. Until recently, no Howler Monkey was known to use tools. However, in 1997 a Red Howler was reported to use a stick as a club to hit a two-toed sloth that was resting in its tree. This opens the possibility that other howlers, such as the Mantled Howler, may also use tools in ways that have not yet been observed.

Reproduction

The Mantled Howler uses a polygamous mating system in which one male mates with multiple females. Usually, the alpha male monopolises the breeding opportunities, but if the alpha male is distracted, a lower ranking male can get an opportunity to mate. And in some groups, lower ranking males do get regular mating opportunities. Alpha males generally maintain their status for about 2 1/2 to 3 years, during which time they may father 18 or so infants. Adults invite mating by flicking their tongues. Females apparently also use chemical signals, since males smell the females' genitals and taste their urine.

The gestational period is 186 days. Births can occur at any time of year. The infant's fur is silver at birth, but turns pale or gold after a few days. After that, the fur starts to darken, and the infant takes on the adult coloration at about 3 months old.

The infant is carried under its mother, clinging to its chest, for the first 2 or 3 weeks of its life. After that, it is carried on its mother's back. At about 3 months the mother will usually start to push the infant off, but will still carry the infant some of the time until it is 4 or 5 months old. After the young can move on its own, the mother will still help it cross difficult gaps in the trees by carrying it across. Juveniles play among themselves much of the time. Infants are weaned at 1 1/2 years old at which point maternal care ends. Adult females typically have an interbirth interval of 19–23 months, assuming the prior infant survived to weaning.

Females become sexually mature at 36 months, and males become sexually mature at 42 months. The Mantled Howler differs from other howler monkey species in that the males' testes do not descend until he reaches sexual maturity. Upon reaching sexual maturity, the young monkeys are usually evicted from the natal group, although the offspring of a high ranking female may get to stay in its natal group. However, many infants do not reach sexual maturity; high ranking adults sometimes harass or kill the offspring of lower ranking monkeys to eliminate competition for their own offspring. When a male from outside the group ousts the previous alpha male, he normally kills any infants so that the mothers come into estrus quickly and are able to mate with him. Predators such as cats, weasels, snakes and eagles also kill infants.

The Mantled Howler is known to be able to live to at least 25 years old.

Conservation

The Mantled Howler is regarded as "least concern" from a conservation standpoint by IUCN. However, its numbers may be impacted by rainforest fragmentation which has caused forced relocation of groups to less habitable regions. 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. The Mantled Howler is important to its ecosystems for a number of reasons, but especially in its capacity as a seed disperser and germinator. Dung beetles, which are also seed dispersers as well as nutrient recyclers, also appear to be dependent on the presence of the Mantled Howler.

The Mantled Howler is protected from international trade under Appendix I of the Convention on International Trade in Endangered Species (CITES). It is most at risk from rainforest fragmentation which has caused forced relocation of groups to less habitable regions.

Taxonomy

The Mantled Howler belongs to the New World monkey family Atelidae, the family contains the howler monkeys, spider monkeys, woolly monkeys and muriquis. It is a member of the genus Alouatta, the genus containing all the howler monkeys. It is sympatric with another howler monkey species, the Guatemalan Black Howler, A. pigra, over a small part of its range, in Guatemala and Mexico near the Yucatan Peninsula.

No subspecies are currently recognised, however, several have been proposed:

Two additional subspecies of the Mantled Howler are sometimes recognised, but are more generally recognised as subspecies of the Coiba Island Howler, Allouatta coibensis, although the evidence is not conclusive:

References

External links

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