Spix’s Red-Handed Howler Monkey, Alouatta discolor
SPIX'S RED-HANDED HOWLER MONKEY
Alouatta discolor
Geographic Distribution and Habitat
The Spix’s red-handed howler monkey, also known as the red-handed howling monkey, or Spix’s howler monkey, is native to central Brazil, specifically along the southeastern Amazon River in the State of Pará and extending slightly into the State of Mato Grosso. They occur mainly in the land area between four rivers, Tapajós, Juruena, Xingu, and Iriri. Within this area, they inhabit lowland forests separated by dry areas, as well as forests affected by seasonal flooding.
The Spix’s red-handed howler monkey was once considered a subspecies of the red-handed howler monkey (A. belzebul). The two are now treated as separate species.
Size, Weight, and Lifespan
With regard to size and weight, there is sexual dimorphism between males and females, or noticeable physical differences between genders. Males have a head-body length ranging between 1.87-3 feet (570-915 mm), along with a tail 2.13-2.2 feet long (650-675 mm), and weigh between 14.33-17.64 pounds (6.5-8 kg). Females have a head-body length ranging between 1.53-1.87 feet (465-570 mm), along with a tail 1.98-2.13 feet long (605-650 mm), and weigh between 10.58-13.67 pounds (4.8-6.2 kg). Males also have longer canine teeth, averaging 0.63 inches (16.08 mm) compared to females, which average 0.35 inches (8.91 mm).
The exact lifespan of the Spix’s red-handed howler monkey is not known, but howler monkeys in general have lifespans of 15-20 years in the wild.
Appearance
The Spix’s red-handed howler monkey is covered in dark brown to black medium-length fur, which contrasts with their red to reddish-brown hands, feet, tip of the tail, and a band down the back. They are stout in appearance and often exhibit a beard that blends into their fur. The hairs along their sides are longer in comparison to those covering the rest of the body. The thick and coarse fur is absent from the underside of the lower portion of the tail, which allows for a better grip when traversing branches high up in the canopy. The face is naked and black in coloration. Their loooooong tails are prehensile, which means they are used for grabbing or grasping.
One of their most prominent and unique features is that of their enlarged hyoid bone. The hyoid is a cup-shaped bone that contains an air sac and is located below the jaw. Acting as a resonating chamber, this modified hyoid bone, along with a modified larynx, is responsible for the legendary roars, grunts, and barks howler monkeys are able to make. Howlers are especially dexterous, as their thumb and index finger are opposable to the remaining three fingers.
Infants have a light band on their back, or no band at all.
Diet
The Spix’s red-handed howler monkey is primarily frugivorous, or fruit-eating, with fruit making up 55.6% of their diet. The rest of their diet consists of young leaves (19.8%), flowers (5.7%), mature leaves (5%), bark (4.4%), and soil (0.4%). Like their nearly-identical cousin, the red-handed howler monkey, it is unclear whether they eat soil because it aids in the digestion of the leaves they consume, or to supplement minerals to their diet. Fungi may also be consumed to aid in the digestion of the increased plant matter at times when fruit supply may be limited.
Behavior and Lifestyle
The Spix’s red-handed howler monkey is diurnal, or most active during the day, and arboreal, preferring to spend their time in the trees.
All howler monkeys generally move quadrupedally, or on all fours, on the tops of tree branches, usually grasping a branch with two hands, or one hand and the tail at all times. Their strong prehensile tails are able to support their entire body weight. Fully grown adults don’t often rely on their tails for full-body support, but juveniles do so more frequently.
With regard to an activity budget, the following has been documented: 58.7% of the time is dedicated to resting, 20% is spent foraging, 14.2% is spent traveling, 5% “other”, and 2.1% is engaging in social activity such as grooming and playing. Nights are spent sleeping in “sleeping trees”. Spix’s red-handed howler monkeys tend to retire to their sleeping trees earlier in the wet season compared to the dry season, and most sleeping trees have a canopy covered with vine tangles, allowing individuals to be well hidden while sleeping.
Besides humans, predators of the Spix’s red-handed howler monkey include jaguars, cougars, snakes, and birds of prey such as the Harpy eagle. They avoid predators in a variety of manners, including howling to both scare the predator and warn others of the danger, hiding in dense foliage, and living in the trees where they are out of reach, or at least, harder to reach.
THEY! ARE! LOUD!!!: Howler monkeys are widely considered to be the loudest land animals. According to the Guinness Book of World Records, their vocalizations can be heard clearly for three miles (4.8 km)!
They don’t look like us, but they do LOOK like us: Howler monkeys are the only Latin American monkeys in which both males and females have full-color vision! In some Latin American monkey species, only females possess this benefit. Most Latin American monkeys have dichromatic vision, seeing primarily blues and greens.
Spix’s red-handed howler monkeys generally live in groups of four to 11 individuals, consisting of one or more males—of which one is dominant— multiple females, and their offspring. Their home range is relatively small, ranging between 12.36 and 111.2 acres (5-45 ha). Like other howler monkey species, upon reaching maturity, members of both genders leave their natal group to join or make groups of their own.
On the left bank of the Santa Helena River, the species is sympatric with, or occurs in the same area as, the Purus red howler monkey (A. puruensis).
As their name implies, vocal communication plays an important role in their social behavior. All howler monkeys have an enlarged hyoid bone and larynx, which help them produce their loud vocalizations. Males generally call at dawn and dusk, as well as scattered times throughout the day. Their main vocals consist of loud, deep, guttural growls or “howls”.
Howling is thought to relate to maintaining spacing between different family groups, protecting group territories, as well as possibly mate-guarding. Howler monkeys call usually when they’re in areas with major feeding sites, which, in turn, leads to advertising these major feeding sites to other groups. The howling also demonstrates their willingness to defend these locally available fruit sources.
Very little information is known regarding the reproductive habits of the Spix’s red-handed howler monkey and has to be inferred from other species, namely the red-handed howler monkey. What is known through one study in 2000 is that mating lasted on average 40 seconds, before which the male offered to groom the receptive female. From the same study, three births were reported in April, August, and September, which is during the food-abundant wet season. One of these births occurred in a tall tree with its canopy covered with vines, likely to serve as protection from predators. Outside of this study, it is known that like all other howler monkeys, upon reaching sexual maturity, individuals of both genders will leave the natal group (the troop into which they were born) to join or start a new group.
Red-handed howler monkeys are polygynous, meaning that one male has multiple female partners. Female red-handed howler monkeys reach sexual maturity at four years of age, while males reach this milestone at around age five. Males, however, will not mate until they achieve a status within a group they have recently joined or made.
Females, who generally give birth every two years, are courted by dominant males through howls and competition with other males. The howls are deemed either acceptable or unacceptable by females. These howls also intimidate other males from neighboring groups who may show interest in the females. Females are receptive every 13 to 24 days and are pregnant for approximately six months before giving birth to a single infant. On rare occasions, they will have twins.
Female red-handed howler monkeys invest heavily in their young by carrying them through the treetops, general care, and providing them with a constant supply of milk. There’s some evidence that the differences in maternal care may be cultural and vary among groups, as some females have been observed carrying their infants against their stomachs, while others carry the infants on their backs.
As frugivores, the Spix’s red-handed howler monkey aids in the regeneration of their forest habitats by dispersing seeds through their feces as they move around their habitat. They also play a role in pollination. Like bees and butterflies, they collect pollen from flowers when consuming them. They then deposit pollen on each flower they visit, thereby pollinating the plants. In addition, by feeding extensively on young leaves, the Spix’s red-handed howler monkey largely strips trees of their young leaves. This stimulates the trees to recover by producing a new set of young leaves within a week, thereby increasing their productivity and growth rate. Finally, as a prey species, they also play a role in feeding local predators within their range.
The International Union for Conservation of Nature lists the Spix’s red-handed howler monkey as Vulnerable (IUCN, 2020), appearing on the IUCN Red List of Threatened Species.
The main threat to the Spix’s red-handed howler monkey is deforestation driven by numerous factors, including: logging, agriculture, cattle ranching, mining, expanding rural settlements, and paving of both the Cuiabá-Santarém and the Transamazon highways. Hunting for local bushmeat is another threat facing this species of howler monkey.
The Spix’s red-handed howler monkey is listed in Appendix II 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.
The species is found in numerous protected areas, including Tapajós National Forest, Jamanxim National Park, Itaituba 1 and 2 National Forests, Altamira National Forest, Tapajós Environmental Protected Area, Jamanxim National Forest, Trairão Environmental Protected Area, Riozinho do Anfrísio Extractive Reserve, and Cristalino Private Reserve of Nature Patrimony.
Conservation actions needed to protect the Spix’s red-handed howler monkey should involve additional land, water, site, and area protection and management. Additional research on the species’ population size, distribution, and trends is needed, as well as further monitoring of their population trends. These steps are crucial if this loud and proud howler monkey can survive the plight of endangerment and extinction.
- https://www.alltheworldsprimates.org/Members/Home/MasterPrimate.aspx?tid=967
- https://animalia.bio/spixs-red-handed-howler
- https://a-z-animals.com/animals/howler-monkey/
- https://www.bioexplorer.net/animals/mammals/monkeys/spixs-red-handed-howler/
- https://boneclones.com/product/howler-monkey-hyoid-KO-179
- https://en.wikipedia.org/wiki/Howler_monkey
- https://en.wikipedia.org/wiki/Spix%27s_red-handed_howler
- https://www.gbif.org/species/5786091
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- https://www.iucnredlist.org/species/43912/190416507
Written by Sienna Weinstein, December 2024