Mantled Howler, Alouatta palliata
MANTLED HOWLER
Alouatta palliata
Geographic Distribution and Habitat
The most widely distributed of the howlers, the mantled howler monkey is found in Colombia, Costa Rica, Ecuador, Guatemala, Honduras, Mexico, Nicaragua, Panama, and Peru. They are mostly found in primary forests (forests that have not been disturbed by human activities), which have more of the tree species they rely on, making food more abundant in these areas. They also prefer riparian forests, along the edges of rivers, over dry deciduous forests. While these areas are preferred, with expanding human developments mantled howler monkeys can also be found near villages and farmland.
With how widespread the mantled howler monkey is, several sub-species have been identified across different regions. These include the Ecuadorian mantled howler (A. palliata aequatorialis), found along the coast of Colombia, Ecuador, Panama, and Peru and may also be found in Costa Rica; the Mexican howler (A. palliata mexicana), found in Mexico, and the golden-mantled howler (A. palliata palliata), found in Costa Rica, Guatemala, Honduras, and Nicaragua.
Two other howler monkey species in Panama are also sometimes recognized as subspecies of mantled howler monkeys. These are the Coiba Island howler monkey, A. palliata coibensis, and the Azuero howler (A. palliata trabeata). However, they are sometimes recognized as subspecies of the Coiba Island howler (A. coibensis), which is suggested by some scientists to be a separate species from the mantled howler monkey due to morphological differences. Despite these differences, DNA analysis didn’t find enough difference between the Coiba Island howlers and mantled howlers to conclude that they are, in fact, fully separate species, making this a slightly murky corner of the mantled howler monkey’s taxonomy. They are still listed on the IUCN Red List as a subspecies of the mantled howler.
Size, Weight, and Lifespan
The body length of mantled howler monkeys ranges from 15–23 inches (38–58 cm), not including their tails which can range in length from 20–26 inches (52–67 cm). They are slightly sexually dimorphic, with females weighing about 9–11 pounds (4–5 kg) and males 13–15 pounds (6–7 kg). At birth, infants weigh only about a tenth of their mother’s weight at 0.9 pounds (0.4kg).
Mantled howler monkeys have been documented to live up to 20 years in the wild.
Appearance
Similar to other howler species, the mantled howler monkey has a stocky build. Their faces are bare and black with a permanently “glum” expression, although it’s hard to imagine looking so sad when they also have such luscious beards. Males have longer beards than females. Like many other primates found in Latin America, mantled howler monkeys are equipped with a prehensile tail which allows them to grip branches while hanging upside down eating leaves. Their tails are even able to save them from a fall should they lose their balance while high in the forest’s canopy. To ensure a firm grip, the underside of their tails is bare with ridges similar to fingerprints. Also like fingerprints, the patterns of these ridges are unique to each individual.
What sets the mantled howler monkey apart from other howlers, at least in their appearance, is the long guard hairs (long, coarse hairs that provide protection from the elements) that drape over their sides almost like a golden cloak against the rest of their black fur. At birth, infants have silvery or golden-brown fur. Their fur changes in color to match their parents by twelve weeks of age.
Diet
Like many other monkeys found in Latin America, mantled howlers have a frugivore-folivore diet (meaning they eat fruits and leaves). To reduce feeding competition with the other monkeys they share space with, howlers focus more on the wide variety of leaves they can feed on rather than the fruit that other Latin American monkeys prefer. You could say that howler monkeys are true leaf connoisseurs, as they are very selective about which leaves meet their standards. Of all the leaves available throughout the rainforests, they mostly eat new leaves which contain fewer tannins and mature leaves from plant species that have a higher protein content and few to no tannins. Being so selective despite the wide variety of fruits and leaves available to them allows the howlers to optimize their diet throughout the seasons, eating young leaves and flowers that are available during the wet season and mature high-protein leaves and fruits in the dry season.
Another way mantled howler monkeys get the most nutrients they can out of their food is with specialized adaptations. Tannins are a type of acid produced by many plant species as protection from herbivory because it doesn’t taste very good, and can also make necessary nutrients in the plants difficult for animals to digest. Other than choosing foods that are low in tannins, the mantled howler monkeys also have a specialized protein in their saliva called tannin-binding salivary proteins (or “TBSPs” for short), that essentially neutralize any negative effects from the tannins. Additionally, compared to other primates close in size, howlers take an exceptionally long time to digest their food, giving their bodies lots of time to absorb as many nutrients as possible from their food.
Mantled howler monkeys have routine trichromatic vision, meaning both males and females can see the same range of colors as us humans, which is somewhat unique among Latin American primates. Scientists think this allows mantled howlers to select the best fruit for their dietary needs.
While they love their meticulously selected leaves, howlers will sometimes also feed on other items including gums, fungi, and honey. They have also been known to unintentionally consume insects on the plants they eat, which researchers believe may give them an extra bit of protein and other nutrients.
Behavior and Lifestyle
Mantled howler monkeys are arboreal, meaning they spend most of their time in the trees, although they will occasionally travel along the ground between tree patches when they need to. They are active during the day, making them diurnal. During the night they’ll sleep stretched out on tree branches.
When near human developments, mantled howler monkeys are at risk of attacks from domestic dogs when they need to travel across the ground. They are also at risk of predation from jaguars, ocelots, pumas (a.k.a., mountain lion, cougar, or panther), some birds of prey, and boas.
Because the mantled howler monkey is so widespread, they are known by multiple names across the many different cultures that encounter them. These names include: “mono congo” in Costa Rica; “monos zambo” in some regions of Mexico, and “buhurum uutzu” in the native language of the indigenous people in Los Tuxtlas, Mexico.
The indigenous people of Los Tuxtlas believe that changes in the mantled howler monkeys’ calls (specifically when they become louder and more frequent) indicate that there will soon be changes in the weather.
Mantled howler monkeys like to take things slow. They begin their days early in the morning with a chorus of long calls, which researchers think lets neighboring howler groups know where their territory is and not to enter it. After serenading the forest, mantled howler monkeys will then take a mid-morning nap before they begin foraging. Because it takes more energy to digest all the leaves they consume, mantled howler monkeys are generally slow-moving and sleepy as they go about their day. They’ll spend about 60-70% of their time resting.
Their home ranges can be 0.012–0.293 square miles (3.2–76 ha), of which they’ll travel around 0.129–0.784 miles (0.207–1.261 km) throughout the day while searching for the best leaves to eat. They live in groups with multiple males and females and group sizes average 10-20 individuals, but can range anywhere from 2–45. While foraging for food, the direction of the group is often lead by pregnant females, likely because of their higher nutritional requirements compared to other group members. Researchers think this also allows pregnant females greater access to food resources.
Males and females each form their own social hierarchies, which are subject to change as adults of both sexes transfer between groups. Males will transfer out of their natal group (the group they were born into) at a younger age than females, with males transferring at 15-36 months, and females transferring at 24-40 months. Unlike many other primate species, younger adults will be dominant to older adults.
Mantled howler monkeys share their habitat with a number of species, including capuchins (genus: Cebus) and spider monkeys (genus: Ateles). Generally mantled howlers get along peacefully with their fellow primates, but can occasionally get into scuffles over food. In areas where mantled howler monkey overlaps with black howler monkeys, they have been known to hybridize.
Characteristic of howlers, the hyoid bone in mantled howlers is enlarged and at an angle to allow them to produce their name-sake calls. The most well-known call of mantled howler monkeys is their long call, which they use to let other groups know where they are and not to mess with them. Both males and females participate in this call, but for females, it is shorter and higher in pitch. Other vocalizations used by mantled howler monkeys include the “deep cluck” which is used by the alpha male to direct the group when traveling and a “grunt” used when an individual is upset. Females will also “wail” to locate their babies when they’ve wandered out of their mother’s view.
Both male and female mantled howler monkeys will urine-wash to “flirt” with the opposite sex, and sometimes in male-male competition for females. They’ll do this by rubbing urine on their hands, the soles of their feet, or even their prehensile tails, which they’ll then use to rub urine across their fur.
Mantled howler monkeys aren’t constrained to a breeding season and give birth year-round. Gestation typically lasts 180-194 days (roughly six months), and females typically give birth every 1–2 years. After birth, babies will ride on their mother’s back for the first year, but start to venture away from her around 12 weeks of age when their adult coloration has come in. When ovulating, the skin around the female’s genitals will change color to signal her fertility. Females reach sexual maturity at 4-5 years of age, and males at 6-8 years.
Although not the most frugivorous primate species, the mantled howler monkey acts as a seed disperser for the fruits that they do eat. Their feces are also used by dung beetles which act as secondary seed dispersers by burying seeds or rolling them away to a new location. This also creates ideal conditions for the seeds to grow in, making dung beetles the gardeners of the forest. Dung beetles will also use feces from the mantled howler monkey’s close relative, the black howler monkey, and likely many other primate species too.
The mantled howler monkey is classified as Vulnerable by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species. Although the most widespread howler monkey, the mantled howler monkey’s population is decreasing. This is largely due to the loss of their habitat due to urban and agricultural development. A side effect of habitat loss is habitat fragmentation, where the once wide unbroken forest has been reduced to smaller patches. The human developments in between the patches are dangerous for mantled howler monkeys and other animals to cross, isolating them from food resources and potential mating partners in other patches.
Groups of mantled howler monkeys that live on the edges of farmland may be tempted to eat some of the crops being grown, which puts them at risk of retaliation from farmers. They are also hunted for bushmeat or to be sold in the pet trade.
Mantled howler monkeys are listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.
In some urban environments, artificial canopy bridges have been implemented to help mantled howler monkeys and other animals cross between forest fragments. Howlers are also known to use powerlines as canopy bridges although, obviously, that is not the intended purpose. Researchers in Costa Rica have advocated for the insulation of powerlines used by howler monkeys to prevent accidental electrocutions from happening, as well as started community reporting of injured howler monkeys to ensure they are brought to a wildlife rehabilitation facility.
Although agricultural development often requires the destruction of forest habitat, some scientists have noted that shade-coffee plantations (a method of growing coffee plants underneath a canopy of trees) may offer an important shelter for howler monkeys who live on the plantations but cause no harm to the coffee plants.
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Written by Lina Rademacher, May 2024