YUCATAN BLACK HOWLER

Alouatta pigra

Geographic Distribution and Habitat
Yucatan black howler monkeys are also called Guatemalan black howlers, Lawrence’s howlers, and Mexican black howlers. In Belize, they are commonly referred to as baboons, although they are not at all related to African baboons. Yucatan black howlers are found in Belize—the location of their most widespread population—northern Guatemala, and southeastern Mexico in the regions of Chiapas, Yucatan, Quintana Roo, Campeche, and Tabasco.

They are endemic to the largest tropical rainforest region of Mesoamerica, Selva Maya, which encompasses over 9 million acres (4 million ha) of land in all three aforementioned countries.

Their habitat is varied and consists of tropical forest, lowlands, deciduous, semi-deciduous (in Calakmul, Mexico, and Tikal, Guatemala), and evergreen forests (in Yaxchilan, Mexico). In riverine habitats, they often avoid the riverbank and remain inland, where they prefer larger trees in the middle to upper canopy.

Yucatan black howler monkey range, IUCN 2020

Size, Weight, and Lifespan
Yucatan black howler monkeys are one of the largest monkeys in the Americas. Their body length is over 2.2 feet (70 cm), with an even longer tail.

They are sexually dimorphic; males weigh much more than females. The average weight for males is 25 lbs (11.4 kg) and for females is 14 lbs (6.4 kg).

Black howler monkeys have a lifespan of 15-20 years.

Appearance
Yucatan black howler monkeys are medium-sized primates with thick, rich black hair covering their entire body, save for a bare spot on the underside of their prehensile tail. Everything about them, from their full face to their spindly fingers, seems rather elongated. Their eyes are small, almond-shaped, and brown and they have a protruding snout.

Male Yucatan black howler monkeys, with an enlarged hyoid bone in their neck, look as though they swallowed a small oval-shaped serving platter that soon became irretrievably lodged in their throat.

Photo credit: Dave Johnson/Creative Commons

What Does It Mean?

Arboreal:
Physically adapted to living primarily or exclusively in trees.

Diurnal:
Active during daylight hours.

Endemic:
Native or restricted to a certain area or country.

Folivorous:
Having a diet that consists of leaves.

Frugivorous:
Having a diet that consists of fruits.

Herbivore:
An animal that feeds on plants.

Quadrupedal:
Using four limbs to move about. This word comes from the Latin meaning “four feet.”

​Sexually dimorphic:
When males and females have different characteristics (size, color, etc.) other than their reproductive organs.

Visit the Glossary for more definitions

Diet
Yucatan black howler monkeys are herbivores. Their diet is both folivorous and frugivorous, with those categories divided up accordingly:

  • Flowers (5%)
  • Mature leaves (30%)
  • New leaves and buds (25%)
  • Other plants (5%)
  • Fruit (35%, their preferred food source)

They have a flexible, adaptable diet that can adjust in cases of habitat change. Despite their habit of consuming leaves, black howler monkeys have a primitive digestive tract more suitable for frugivory. It takes them a very long while to digest properly, so they spend a lot of their time lounging in the trees.

Behavior and Lifestyle
Yucatan black howler monkeys are arboreal, quadrupedal, diurnal, territorial, and highly social. Territory sizes range from 3 to 25 acres (1.2–10 ha), indicated by howling vocalizations.

Aside from sleeping, Yucatan black howler monkeys spend their time resting (70%), feeding and foraging (18%), moving (5%), and socializing (1.2%). The huge allotment given to inactivity is due to the lengthy digestion of leaves.

Yucatan black howler monkeys are often found living in close conjunction with spider monkeys.

Daily Life and Group Dynamics 
A typical group of Yucatan black howler monkeys consists of one dominant alpha male, a few females, their offspring, and occasionally extra males that are likely involved in group defense against predators.

Occasionally there are lone males that try to start their own groups or attempt to usurp males of established groups. As one might expect, newly formed groups are often smaller than long-established ones.

Densities of groups range from 6 to 90 individuals per 0.4 square miles (1 sq km), which is actually lower than most other howler monkey species. Infants and adolescents engage the most in social interactions, especially vocal ones. In general, different groups have quite small and broadly overlapping home ranges.

Fun Facts

The Yucatan black howler monkey is called a “baboon” in Belize. It is not actually a baboon.

It is one of the largest monkeys in Belize and the rest of the Americas.

Howler monkeys are considered by the Guiness Book of World Records to be the loudest land animal.

Communication
Communication is perhaps what the howler monkeys are most famous for, and it’s not hard to discern why. Imagine a large animal, like a cow, an elephant, or, you know, a brachiosaurus. Now imagine a sizeable group of that large animal breathing very deeply and very loudly, all at once in the same rattling, rasping, wind tunnel of a howl. If you’ve been able to successfully imagine all of that, you have a pretty good idea of what a group of howler monkeys sounds like. The description alone, however, does not do their incredibly loud howl justice.

Howling sessions can last for over an hour and they usually take place in the early morning and late evening. They are low frequency and, in case you didn’t get it the first couple times it was mentioned, loud–about 88 decibels at a 16-foot (5-m) distance, though they have been heard from up to two miles (3.2 km) away. For comparison, that’s equivalent to the sound of a subway hurtling past. Even more, prolonged exposure to any noise above 90 decibels can cause gradual hearing loss.

One of the interesting things about howling is that it occurs in staggered rounds when more than one male is present. This means that other male howlers can tell when more than one group is around, which is pretty helpful if you are a rival group and you’re thinking about heading over to size up another alpha male. If the howls indicate that he’s backed up by other males, the opposing male may not want to venture to take the risk of approaching.

Reproduction and Family
Sexual maturity in Yucatan black howler monkeys is reached at the age of four years old. They breed non-seasonally and typically produce one offspring annually. The gestation period lasts about 180 days. Females care for their young for 12 months after birth, providing direct care and protection from predators and from adult male howlers, who may attempt infanticide. Males and other females do not typically assist the mother with raising her offspring.

Only the dominant males or males with high social status will copulate with females. Alpha males are able to copulate more frequently and with more females than those with lower status. Due to the necessity of having to wait to gain a high social status, males often mate later in life than females.

Ecological Role
Yucatan black howlers are important seed dispersers, a result of their frugivorous diet. It is possible that they provide economic benefits to humans because their unique howling attracts eco-tourists to that region of Mesoamerica.

Conservation Status and Threats
The International Union for Conservation of Nature Red List of Threatened Species classifies the Yucatan black howler monkey as Endangered (IUCN, 2020).

Their population trend is listed as “decreasing” and some scientists predict the Yucatan black howler monkey could become extinct in the next 30 years or at least experience a population reduction of 50% or more over the course of three generations.

The main threats for black howler monkeys are accelerated deforestation rates across its distribution and the direct extraction of individuals for pet trade. In Guatemala, a high rate of deforestation has been associated with the rapid expansion of the agriculture frontier due to megaprojects such as African palm and sugar cane, and the destruction of forest due to open mining.

Threats to the Yucatan black howler monkey include:

  • Hunting
  • Residential and commercial development
  • Logging and wood harvesting
  • Habitat destruction and deforestation
    • Forests are being converted into pastures and agricultural plots
  • Disease
    • Yellow fever
  • Abnormal rainfall
  • Natural disasters
    • Storms, flooding, hurricanes
  • Predation
    • Infanticide by adult male Yucatan black howler monkeys
    • Jaguars
    • Pumas
    • Harpy eagles
    • Large arboreal snakes
    • Humans (who capture them as pets and/or occasionally hunt them for food)

Conservation Efforts
The Yucatan black howler monkey lives in many protected areas designed to provide a sustainable and safe habitat. Some of those areas are Guancaste National Park, Blue Hole National Park, Cockscomb Basin Wildlife Sanctuary, Caracol Archaeological Reserve, Rio Bravo Conservation and Management Area, Tikal National Park, and Palenque National Park.

In Belize, a community-based conservation organization called the Community Baboon Sanctuary has protected land along the Belize river to ensure that habitat and food sources are not destroyed for agricultural purposes.

​References:

  • ​https://animaldiversity.org/accounts/Alouatta_pigra/
  • http://www.belizezoo.org/mammals/black-howler-monkey/
  • https://rainforest-alliance.org/species/howler-monkey
  • https://iucnredlist.org/species/914/13094441#conservation-actions
  • http://animalia.bio/guatemalan-black-howler
  • ​http://selvamaya.info/en/mayan-rainforest/the-selva/

Written by Rachel Heim, June 2019