Mantled howler


The mantled howler 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, and males can weigh up to. 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. The male mantled howler has an enlarged hyoid bone, a hollow bone near the vocal cords, which amplifies the calls made by the male, and is the reason for the name "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 groups are usually smaller. Most mantled howlers of both sexes are evicted from the group they were born into upon reaching sexual maturity, resulting in most adult group members being 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 affected by deforestation, it is 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.

Taxonomy

The mantled howler belongs to the New World monkey family Atelidae, the family that contains the howler monkeys, spider monkeys, woolly monkeys and muriquis. It is a member of the subfamily Alouattinae and genus Alouatta, the subfamily and genus containing all the howler monkeys. The species name is A. palliata; a pallium was a cloak or mantle worn by ancient Greeks and Romans. This refers to the long guard hairs, known as a "mantle", on its sides.
Three subspecies are recognized:
Two additional subspecies of the mantled howler are sometimes recognised, but these are more generally recognised as subspecies of the Coiba Island howler, Allouatta coibensis. However, mitochondrial DNA testing of their status has been inconclusive:
  • Azuero howler, Alouatta palliata trabeata, in Panama;
  • Alouatta palliata coibensis, in Panama.

    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 yellow or golden brown guard hairs on the flanks of the body earning the common name "mantled" howler monkey. When the males reach maturity, the scrotum turns white. Females are between in body length, excluding tail, and males are between. The 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, which is smaller than that of several smaller monkey species, such as the white-headed capuchin.
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 cords. This hyoid bone amplifies the male mantled howler's calls, allowing it to locate other males without expending much energy.

Behavior

Social structure

The mantled howler lives in groups. Group size usually ranges from 10 to 20 members, generally 1 to 3 adult males and 5 to 10 adult females, but 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 gets primary mating rights. Animals in the group are generally not related to each other because most members of both sexes leave the group before sexual maturity.
Grooming activity in the mantled howler is infrequent and has been shown to reflect social hierarchy, with dominant individuals grooming subordinates. Most grooming activities are short and are typically females grooming infants or adult males. Aggressive interactions between group members are 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 but interactions with the white-headed capuchin sometimes occur. These are most often aggressive, and the smaller capuchins are more often the aggressors. However, affiliative associations between the capuchins and howlers do sometimes occur, mostly involving juveniles playing together, and at 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. Leaves make up between almost 50% and 75% of the mantled howler's diet. The mantled howler is selective about the trees it eats from, and it prefers young leaves to mature leaves. This selectivity is likely to reduce the levels of toxins ingested, since certain leaves of various species contain toxins. Young leaves generally have fewer toxins, as well as more nutrients, than more mature leaves, and are also usually easier to digest. 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. 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 majority 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 sometimes exceed the proportion of leaves. The leaves and fruit from Ficus trees tend to be the preferred source of the mantled howler. Flowers can also make up a significant portion of the diet and are eaten in particularly significant quantities during the dry season. The mantled howler tends to get the water it needs from its food, drinking from tree holes during the wet season, and by drinking water trapped in bromeliads.
Like other species of howler monkeys, almost all mantled howlers have full three color vision. This is different from other types of New World monkeys, in which most individuals have two color vision. The three color vision exhibited by the mantled howler is believed to be related to its dietary preferences, allowing it to distinguish young leaves, which tend to be more reddish, from more mature leaves.

Locomotion

The mantled howler is diurnal and arboreal. Movement within the rainforest canopy and floor includes quadrupedalism, bridging, 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 the name "howler" from the calls made by the males, particularly at dawn and dusk, but also in response to disturbances. These calls are very loud and can be heard from 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 cords — amplifying the sound made by the vocal cords. 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 as the males'. 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 uses a wide range of other sounds, including barks, grunts, woofs, cackles and screeches. It uses clucking sounds to maintain auditory contact with other members of its group.
The mantled howler also uses non-vocal communication, such as "urine rubbing" when in a distressful social situation. This consists of rubbing the hands, feet, tail and/or chest with urine. It marks its scent by rubbing its throat on branches. Lip smacking and tongue movements are signals used by females to indicate an 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 usually 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.