Old World Monkeys
The classification of Old World monkeys is geographically confused. The 2 subfamilies are Cercopithecinae and Colobinae. Cercopithecines are largely African, though macaques are Asian. Colobines are nominally Asian, though colobus monkeys are African.
The colobine subfamily includes 59 species in 10 genera. Most are medium-sized monkeys with long tails. Colobine monkeys include colobus, douc, langur, leaf, lutung, surili, snub-nosed, and proboscis monkeys.
Most colobines are arboreal, though some are more terrestrial. Their habitats range from rain forests, mangroves, mountain forests, to savanna.
Colobines have diverse colorations. In many species, the coloring of juveniles differs considerably from adults.
Colobines are herbivores, with occasional dietary supplements of insects and other small animals. Leaves are a columbine staple. Leaves are hard to digest, so these monkeys have complex stomachs with multiple chambers.
Red colobus monkeys that live on the island of Zanzibar sometimes eat charcoal to help them handle the cyanide in the leaves they eat. Red colobus monkeys are often able to digest plants that are toxic to other primates.
Proboscis monkeys are endemic to the swampy mangrove forests of Borneo. They are among the minority of monkeys that swim. Proboscis monkeys not only swim, they swim well, both on the surface and underwater. Having partly webbed hands helps. Such is swamp life.
Proboscis eat primarily seasonal fruit and leaves; also, flowers, seeds, and insects as supplements.
Proboscis are one of the largest monkey species in Asia. Males average 72 cm, 19 kg; females 57 cm, 9.5 kg. This is not the only dimorphism.
Proboscis males have a particularly pronounced snoot; enough of a nuisance that some have to push it aside to eat. A female’s nose, while peculiarly prominent for a monkey, is much smaller, and upturned.
A male’s cartoonish nose has its compensation. Females find males with the biggest noses most attractive.
Proboscis monkeys have somewhat fluid sociality. A typical family group has 1 adult male, along with some adult females and their offspring. Females in a group have a dominance hierarchy. Mothers often rear their young with some assistance from other females in the group, particularly close relatives.
All-male groups of up to 20 are also common. Some, mostly males, prefer a more solitary life.
Upon reaching maturity males leave their natal group for an all-male group. Females occasionally leave their natal group for any of a variety of reasons: avoiding inbreeding or infanticide, reducing competition for food, or in hope of elevating their social status.
Females solicit mating. Proboscis monkeys also engage in non-reproductive and same-sex mounting.
There is little territoriality in the overlapping home ranges. Groups gather into bands of up to 60 or more and travel together, though individuals only groom and play with those in their own group. Arguments do arise, but proboscis monkeys are generally tolerant of each other.
Proboscis monkeys have a variety of vocalizations, including alarm and threat calls. Males communicate the status of their group by honking. A special honk is used to reassure infants.
Proboscis monkeys prefer to sleep in trees near a river, perhaps for safety, though crocodiles are its main predator.
Proboscis monkeys need large tracts of forest to sustain themselves. Though protected by law, habitat loss and poaching reduced the proboscis population by over half from 1970–2008. By 2010, their numbers in the wild were down to 1,000 or less. National parks and wildlife reserves are their last enclave. Like many other monkeys, proboscis monkeys will soon be extinct.
The cercopithecine subfamily comprises some 71 species in 12 genera. Cercopithecines include baboons, guenons, macaques, mandrills, mangabeys, patas monkeys, and vervet monkeys. Most are omnivorous.
Most cercopithecines live in sub-Saharan and central Africa, though macaques range from far east Asia through northern Africa, with a presence in Gibraltar.
All cercopithecines have cheek pouches which can store food. This differentiates cercopithecines from colobines.
Otherwise, the various species are adapted to the different habitats they inhabit. Arboreal species tend to be gracile: slender, with long tails; while terrestrial species are more robustly built.
Guenons are a fairly diverse grouping of monkeys. The beautiful Diana monkey is a guenon. The smallest Old World monkey, the talapoin, is also a guenon, as is the fastest primate of all: the patas.
Talapoins may be found in the swamp forests of central Africa. An adult male talapoin weighs 1.3 kg, while a female averages 0.8 kg. Talapoins are 32–45 cm long, excluding the tail. Typical of small monkeys, talapoins are arboreal, living in troops of 50 to 100.
Talapoins are gregarious, with the typical complement of social behaviors, including play, occasional aggression, and grooming. They are not territorial.
At the other extreme from talapoins are ground-dwelling patas monkeys. Patas monkeys have considerable sexual dimorphism. Adult males weigh 12.4 kg, 60–87 cm long (excluding tail); females 6.5 kg, 49 cm.
Patas monkeys are adapted for life on the ground, and are the only monkey built for running. These slender monkeys run on all fours at up to 55 km per hour, faster than any other primate, owing to their long forelimbs.
They need the speed. Patas are preyed on by hyenas, jackals, and leopards. Away from sheltering trees, patas monkeys rely on running away from danger.
Patas monkeys typically live in groups of 20–30, though troops with up over 60 members have been seen. Groups are largely segregated by sex.
During most of the year, a female troop has a single adult male. Females lead the group, while the male is lead only in providing vigilant security. Should a predator appear, the male will try to grab its attention and run away from the troop, while the females flee to safety. Other males temporarily join a female troop during breeding season.
Once a male juvenile reaches sexual maturity, around 4 years of age, he leaves his natal group to join an all-male group.
Patas are tolerant of several types of habitat, ranging from savanna and steppe to woodlands, preferring open areas to heavily wooded forests. Patas live in fairly arid areas.
Patas prefer tall trees to short ones, and spend midday there resting, as well as sleeping in the trees. They forage on the ground in the morning and afternoon.
Diana monkeys live in West Africa. Adults weigh 4–7 kilograms. A Diana may live 2 decades.
Dianas live in in the canopy of primeval forests, rarely hitting the ground. They don’t do well in secondary forests. As such, Dianas are gravely endangered by human habitat destruction.
Dianas are omnivorous, eating anything nutritious and nontoxic: fruit, leaves, flowers, insects, and small invertebrates.
A Diana family group may be 5–10 adults, with a single male and a harem of females. Multiple families make up a troop of up to 50. Breeding is year-round, with a 6-month gestation to a birth of a single offspring.
Like vervets, Diana monkeys have a distinct alarm call for each type of predator: leopards, eagles, chimpanzees, and humans. Communication may be coordinated in a call-and-response. For example, a female may answer a male’s call of a leopard alert, though with a different vocalization that females use for the same animal.
Chimps chase Diana monkeys through the treetops, trying to snag one for a meal. Spotting such a wily predator results in deafening silence and retreat. Others in the troop take note and move off silently too.
Diana monkeys have highly distinctive hair, with sharply contrasting portions. This helps a Diana effectively convey body language, including communicative facial expressions.
Diana monkeys have a reputation for perceptive reliability. The tree-dwelling African hornbill isn’t concerned about leopards but is preyed upon by eagles. The hornbill recognizes a diana eagle warning and responds, while ignoring leopard calls.
Red colobus monkeys live in the same neck of the woods as Dianas. Red colobus associate with Dianas for safety, as either is chimp meat if caught.
When the two forage together, both monkeys respond to a Diana warning. The type of vigilance differs between Diana monkeys and red colobus, so there is more overall protection for both when together.
Vervet monkeys reside in sub-Saharan Africa. They sleep in the trees for safety, but spend their days on the ground, playing and feeding.
Vervets have 3 types of predators: snakes, leopards, and raptorial birds, such as martial eagles. Vervets have names for these predators. Chickens and ground squirrels are also known to have different alarm calls for ground and aerial predators.
If a snake is spotted, a distinctive vervet alarm call is made. Nearby vervets stand up to spy the snake. Once several monkeys have seen the snake, they may approach it as a mob, forcing the snake to retreat.
A leopard raises a cry that has vervets leaping up the trees to small branches where a leopard cannot reach. An air attack possibility gets vervets running for cover after a vervet cries out to look out from above.
The vervet predator language is learned by young ones. Infant vervets often make mistakes, raising an alarm to pigeons, warthogs, or other non-threatening creatures.
While infants may be easily scared into alarm, they quickly cotton to the concept of alien approach, whether overhead or on the ground. By observing adult alarm call and response, a juvenile learns the subtleties of proper calling.
Vervets have other verbal communications specific to an individual or social situation. In other words, vervets gossip. The communications are so nuanced that humans have difficulty discriminating vervet-speak.
Japanese macaques reside in the furthest northern range of all monkeys. They are found on 3 of the 4 main islands of Japan: Honshū, Kyūshū, and Shikoku; but not Hokkaidō, the northernmost island.
Japanese macaques are equally comfortable in the trees and on the ground. Some have learned to swim and to dive into water.
Japanese macaques live 25 to 30 years. They are tough, clever, and learn quickly; typical of the 15 macaque species.
Japanese macaques are omnivores. Their favorite foods are fruits, berries, nuts, and acorns. Flowers, seeds, leaves, and grasses are also good, as are mushrooms. Spiders, insects, larvae, snails, crabs, crayfish, and barnacles provide variety. Some are fond of birds’ eggs when they can be found.
Winter can mean living off tree bark, along with winter tree buds and sprouts. Japanese macaques that live seaside eat the kelp and algae that wash up onto beaches.
Males and females are similarly sized: 60 cm, with the average female 12.3 kg, and 14.6 kg for males. Overall, weight varies between 9 to 18 kg. Males look larger, as they have more muscle and hair on their shoulders and hips.
Japanese macaque troops commonly contain 20 to 100 members. Female Japanese macaques spend their entire life in the same troop. Matrilines develop, albeit at different social strata.
A mother provides all the care for her newborn. As an infant grows, relatives assist. Older siblings pay special attention.
Males sometimes carry, comfort, play with, and protect juveniles. A male may adopt a juvenile that needs attention. Overall, a troop provides a supportive environment for its young, with many willing caregivers.
Males typically emigrate to another troop when they reach maturity, which is between 3 to 7 years of age. The few that stay in their natal troop maintain close ties to their mothers and sisters.
There are separate dominance hierarchies for females and males. Favored males have high social standing. They stay in the central part of the troop with the most dominant female matriline.
The top-ranking male oversees security. The top female leads the troop. The alpha male and alpha female settle disputes between group members.
Males getting ready to leave a troop are relegated to its outer edges, as are males trying to join the group. These peripheral males are low ranking. Low-ranking females sometimes develop friendships with these males.
Many males change troops several times. Some become nomads, joining a troop only during breeding season.
Males compete for females during breading season, but females choose their mating partners. A male’s chances are as much a matter of personality as well as look. Some new males are welcomed, while others are chased away.
As with many monkeys, grooming and play are important facets of macaque social life. Both serve to form and maintain relationships; play more so for the young.
As juvenile male macaques mature, they go off with playmates for longer durations. Young males especially like to play with nearby adult males. In contrast, females stay close to their female relatives, learning by practice on infants their mothering skills.
Home ranges are 5 km2 in the south, and up to 20–30 km2 in the north, where food is scarcer. Troop ranges may overlap.
Neighboring troops try to avoid each other. They let each other know where they are by shaking treetops. Chance encounters are most often trouble-free, but fighting can occur.
Imo the Innovator
Researchers studying Japanese macaques once doled out sweet potatoes on a sandy beach to entice monkeys into the open. The monkeys would rub the sand off before munching. Then, a 2-year-old, low-ranking female that researchers named Imo, which is the Japanese word for sweet potato, had the insight that washing was a superior technique.
Imo took her taters to a nearby freshwater stream to wash them off. Within a short time, Imo’s friends and family followed her lead, and rinsed their potatoes in the stream. Inside of a decade, spud washing was practiced by 90% of the troop.
Then Imo had another idea: salted potatoes. Imo started washing her potatoes at the seashore.
Again, Imo started a trend that became a tribal norm; over 80% within 5 years. The tradition continued through generations, long after Imo was gone. That troop of Japanese macaques treat themselves to sea-rinsed potatoes whenever they get the chance.
Imo also figured out how to sort wheat from sand by dropping it into water. Whereas sand sinks the wheat floats. This technique also caught on with the tribe.
Deep winter snow in the mountain forest on Honshū makes for mean foraging. One Japanese macaque troop acquired the luxury of bathing in natural hot springs to take the chill off; a learned behavior passed on through generations.
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As with much of the natural world, the lives of Japanese macaques are being degraded by humans, who pave roads and cut down trees. As their habitats shrank, Japanese macaques became regarded as encroaching into human territory: raiding crops and coming into towns. To many Japanese people now, having taken macaque territory, the indigenous monkey has become a pest.
A 1948 national law protecting the species is adhered to in the breach by permits to kill those that pillage on human land. Japanese macaque populations are on an inexorable decline toward extinction.