COLOMBIAN RED HOWLER
Geographic Distribution and Habitat
The Colombian red howler is found throughout the Western Amazon Basin in South America, with populations recorded in Brazil, Colombia, Ecuador, Peru, Trinidad and Tobago, and Venezuela. Their range blends extensively with the ranges of other howler monkey subspecies. They live in several types of forest, including primary lowland rainforest, dry deciduous forest, Andean cloud forest, gallery forest, mangrove swamps, and várzea forest (in which the trees are seasonally flooded by whitewater rivers). They live as high up as 10,500 feet (3,200 m), though they’re more common between 650 and 2300 feet (200 and 700m). The home ranges of local populations vary with the abundance of their preferred fruits and leaves. During the fruit scarcity season, for instance, some groups respond by sticking to particular areas of flooded forest and becoming more specialized in their foraging habits. However, howler monkeys generally have small and overlapping ranges that vary from 54 to 450 acres (22–182 hectares).
In recent years, and because of their vast range, there has been quite a bit of controversy around designating red howler monkeys species and subspecies. Recent genetic and morphological analysis have eliminated subspecies specifically related to red howler monkeys. As of this writing, the IUCN (International Union for Conservation of Nature) recognizes five red howler monkey species. They are the Colombian red howler (Alouatta seniculus), the subject of this Primate Species Profile, the Bolivian red howler (Alouatta sara), the Guyanan red howler (A. macconnelli), the Jurua red howler (Alouatta juara), and the Purus red howler monkey (A. Puruensis).
Size, Weight, and Lifespan
On average, adult males weigh 16.6 pounds (7.54 kg) and measure 19.3–28.4 in (49–72 cm), while adult females weigh 13.9 pounds (6.29 kg) and measure 18–22.4 inches (46–57 cm). Unconfirmed estimates suggest that Colombian red howlers can live up to 25 years in the wild.
Both male and female howlers sport reddish-brown fur in shades that shift as they age. Their stubby gray noses and mouths and enlarged voice boxes, which droop beneath their chins like thick red beards, make for a statuesque, almost rabbinical appearance. When howling, they pucker their lips and seem to lean their weight into the sound. The undersides of the last third of their prehensile tails are furless to allow for a firmer grip on tree branches. Males and females are roughly the same size.
Colombian red howlers are folivores—their diet consists mostly of leaves (a little more than 50%) with fruit making up most of the remainder, as well as buds, flowers, seeds, moss, twigs, stems, and soil from termite hills. Consequently, their foraging range is much smaller than that of frugivorous (fruit-based) subspecies, since leaves are more common than fruit. They will, of course, opt for fruits and sugary flowers when given the option, but they can happily sustain themselves on leaves for long periods of time.
Their digestive system is somewhat specialized for leaves. Two large sections in their hindgut contain bacteria that can extract key nutrients from leaves. Other physical adaptations for leaf-eating include deep lower jaw bones and narrow incisors. They’re especially reliant on young, more tender leaves.
Primatologists often describe their diet as “opportunistic,” since their preferences become more general or specified depending on seasonal and ecological changes. This flexibility makes it easier for the monkeys to adjust to forest fragments and degraded habitats. In one 2011 field study, a group of Colombian red howlers quickly switched from leaves to epiphytes—non-parasitic plants that grow on other plants, like orchids and ferns—after flooding covered most of the leaves in their local range.
Behavior and Lifestyle
Colombian red howlers spend most of their lives in the upper canopy. Due to the demands of digesting leaves, which comprise the majority of their diet, they rest in the trees for up to 70% of the day. They spend 5–10% of the day moving and the rest feeding.
Early in the day, Colombian red howlers acquire as much food as possible and forage less and less as the hours pass. Primatologists suggest that this pattern occurs due to adverse weather conditions later in the day, which also make it difficult to develop consistent patterns of behavior beyond resting. Relatedly, the howlers shift from quantity to quality in the late day and opt from energy-rich food sources to sources with high protein content. They consume about 2.7 pounds (1.23 kg) of food daily.
Red howler groups range from 2–13 animals. In Colombian red howler populations, they average 5.5–9 individuals. There is usually one dominant male in the group, a harem of 2–5 females, and a number of juvenile or sub-adult males.
Among most primates, allogrooming is an activity in which troop mates groom one another. As well as the resulting health benefits of removing insects and parasites from each other’s coats, is it a bonding and de-stressing exercise that strengthens group alliances. Grooming rates vary widely between red howler monkey groups. In groups that include high populations of related females, which result in stronger coalitions, grooming is more common.
Both males and females often (but not always) leave their natal troops upon reaching sexual maturity. Adult males may then live alone for a time before attempting to oust the dominant male in a pre-existing group. If successful, he will acquire the existing harem of females and kill their infants to expedite their readiness to conceive again. This is a practice known as “infanticide,” which is not uncommon in the animal kingdom when a new dominant male takes over an existing community. It ensures that all future offspring will be his alone.
Females usually join a new troop soon after leaving their natal group or when they begin a consortship with another solitary male.
As their name suggests, Colombian red howlers (along with other howler monkey subspecies) are known for their incredibly loud, hoarse, low-pitched howls—the loudest in the animal kingdom—which is most common during their “dawn chorus,” a regular morning session of howls (usually by males) audible from up to 1.3 miles (2 kilometers) away. The powerful roars rely on their enlarged voice boxes, which serve as resonating chambers for the sound.
Early theories as to the purpose of the dawn chorus in howler monkeys suggested that it helped troops establish intergroup spacing for the day. However, in red howlers, the roaring continues throughout the daytime. Several different uses for daytime howling have been suggested, most of which concern the constant and immensely competitive process of deterring other males and attracting females. Some (non-exclusive) possibilities include deterring outside males from entering the group, solidifying bonds with subordinate males, and indicating fitness to nearby females. Like chest-beating in gorillas, roaring may serve as a marker of strength to both sexual competitors and prospective mates, which limits the need for dangerous and potentially fatal fights between males.
Red howlers also emit short calls to nearby troop members while foraging, as well as a broader repertoire of grunts and barks. However, little research is available on the possible functions of vocalizations other than their howls. Other howler monkey subspecies also rely on chemical communication—for instance, by rubbing urine on their palms and the soles of their feet—but this behavior has not been recorded in red howlers.
In related howler species, menstrual periods last for 2–4 days and occur roughly 17 days apart. Pregnant red howlers give birth every 17 months or so, though the interval may shorten if their most recent infant dies. Females first give birth around 5 years, while males father offspring around 7 years. Sexual competition is fierce due to an unbalanced sex ratio—more males are born than females—and polygynous mating practices, in which a small number of males (usually one per troop) mate preferentially with a larger number of females.
Male howlers fight often when competing for females (but rarely otherwise), and these fights are often dangerous for both parties. Their competition sometimes includes infanticide, especially if new males join a group. However, infanticide is less likely if natal juvenile males (born in the group) are present, as this prevents other males from joining.
Sexual interactions start with “consortships,” when a male and female begin spending lots of time close to one another. Eventually, the female initiates copulation with the male by approaching him and moving her tongue rhythmically.
Infants are usually born during the dry season so that they can be weaned during the wet season when food is the most abundant. They begin using their prehensile tails at one-month-old to hang onto their mothers. Females in the group are attentive and tolerant of the infants, especially in the earliest parts of their life. Males are also tolerant (so long, of course, as the offspring is theirs).
Colombian red howlers, and howler monkeys in general, eat dozens of different plants and, as a result, spread the seeds of many species in their fecal matter. One study found 2.3 species per stool sample in a population of howlers. Importantly, the population studied in this case followed a less diverse diet than populations in other forest types. This means number is probably low and that a higher number of plant species per sample is likely in other groups.
For some tree species, howler monkeys are the only seed dispersers, especially in forests disturbed by human activity. They thus contribute to “secondary succession” by restoring degraded habitats through seed dispersal. Notably, studies have found that passing through the howler gut has a positive effect on the survival of seeds and that nutrients in their stool contribute to the health of germinating seedlings.
The International Union for Conservation of Nature lists Colombian red howlers as Least Concern (IUCN, 2021), appearing on the IUCN Red List of Threatened Species.
Hunting, deforestation, disease, and other human-caused pressures are the greatest threats facing Colombian red howlers. In Colombia, their habitats have been extensively deforested. In Peru, a combination of hunting for bushmeat, agricultural deforestation, and ranching, among other pressures, has led to their local extinction in certain areas.
Damming and hydroelectric agriculture are especially harmful to red howlers since the necessary infrastructure affects water levels in the flooded forests they inhabit during the wet season. These practices have been especially harmful to howlers in Brazil. In Trinidad, red howlers are also threatened by invasive species of birds and primates, and hunting laws are poorly enforced. Occasionally, they are killed for their enlarged hyoid (a U-shaped bone in the neck that supports the tongue) or skin.
Their behavioral and dietary flexibility has allowed them to survive these pressures with fewer consequences than other primates. Nonetheless, their population is decreasing, and many howlers now inhabit forest fragments that limit their ability to avoid inbreeding by joining new troops.
Colombian red howlers are 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.
In nearly all countries inhabited by Colombian red howlers, national parks and nature reserves protect large swaths of local populations from hunting, habitat loss, and other threats.
- https://d1wqtxts1xzle7.cloudfront.net/38535663/1997_Folia_Primatol-libre.pdf?1440177569=&response-content-disposition=inline%3B+filename%3DDiet_and_social_behavior_changes_in_a_re.pdf&Expires=1691002383&Signature=SxnfuQtGrmWiaQdiX-HHrdbxOT2JB6D-epL3dRk yHblgACRKU9PYqpgYhtxAz2Owmvu0P15pnHkRFCAFao5frVmGvKUj9okeGPFAC7MKj7ZY0PoSIl1VkMq7cWB7USoeJIZhzevM6ovWGGRGo0YhrFURUBRWyDCp0uWTtW-b7CEO~nlUC8xhFCNPh-CeN9wlEkfHeOJeRBL3JY4OgoeitJURTjr3-Gn-5S2pGSgDjwNCX4dBGYwY5StjzkCZPsf3-iALAWvBGmDb2f6gfxYGT5XVXhFidUoC73boFU1cLMPaio~uTPJQScfG4rnIgnV1ROEp36mnyTcA0MpRoe7fg__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA
Written by Eli Elster, August 2023