Monkeys From Heaven

Hanuman langurs use shrewd strategies and poison-proof stomachs to survive in some of India's most extreme environments

06-01-2003 // Rene Ebersole
National Wildlife Magazine Image - Animal

THE LEGEND of the sacred monkey traces back more than 20 centuries to an old Hindu epic of Hanuman, the god of monkeys. In a battle of good versus evil, Hanuman leaps from the coast of India to rescue his king’s abducted queen from the island of Lankah (present-day Sri Lanka). Setting the island kingdom ablaze with his tail, Hanuman distracts the queen’s captors and sets her free. Today, the fabled deity is still worshipped for his brave deeds—his charred face and limbs a national symbol of strength.

Many devout Hindus regard the black skin of Hanuman langurs as proof that they are the living descendants of the monkey god. But the mysterious intrigue surrounding these monkeys doesn’t stop with their royal legacy. For decades, scientists have marveled at their social behaviors—some of them jarringly violent—as well as Semnopithecus entellus’s dogged ability to survive in a diverse range of environments, from the brutally hot sands of the Great Indian Desert to the snow-capped Himalayan Mountains. Next to man, the Hanuman langur inhabits a wider array of landscapes than any other primate in the world.

Visit the imperial city of Jodpur on the edge of the Thar Desert and you are likely to see the silver silhouettes of Hanuman langurs lounging on rooftops. The monkeys’ settlement in urban jungles is linked tightly to their sacred status, which ensures them safety and a steady surplus of leftovers, vegetables, water, rice and sweets from Hindus and other passersby. "The Hindus honor God Hanuman by provisioning the monkeys," says Andreas Koenig, an anthropologist at the State University of New York–Stony Brook, who with his wife, Carola Borries, has been studying Hanuman langurs for many years. Save for the occasional sandwich snatching or pantry raid, the monkeys are mostly celebrated by their fellow urbanites. They have even been spotted grooming stray dogs, which are known to hunt and kill monkeys.

National Wildlife Magazine Image - Animal

Photo: © CYRIL RUOSO (BIOS/PETER ARNOLD INC.)

CITY LIFE: Adaptive Hanuman langurs move atop the urban canopy with the same ease that they exhibit in the treetops of their forest homes.

The Hindus make it possible for thousands of Hanuman langurs to survive in cities and near remote desert temples. But researchers say the key to the Hanuman langur’s success across its wide range—from India to Pakistan, Sri Lanka, Nepal, Bangladesh, and possibly as far east as Bhutan and China—is its gut. "They can live on anything, even strychnine," explains Sarah Hrdy, an anthropologist at the University of California–Davis. Like all colobines (leaf-eating monkeys), Hanuman langurs have special "sacculated" stomachs that are extremely efficient at breaking down plant materials—mature leaves, unripe fruit, seeds, bark. Their stomachs support anaerobic bacterial colonies that digest cellulose. On India’s Mount Abu, where Hrdy studied Hanuman langurs during the early 1970s, a pungent invasive shrub called Lantana camara grows widely. "The black berries of that plant will poison a horse," says Hrdy. "Yet there are periods of the year when the langurs subsist entirely on lantana berries."

According to experts, some 17 species of langurs—or leaf monkeys, as they are also known—exist worldwide, and the Hanuman langur is one of four species in India. Among Hanuman langurs, there may be anywhere from 7 to 15 subspecies, which vary in body mass, size and color—from gray to dark brown to golden. The average weight of a female is 25 pounds, while the typical male weighs around 40 pounds.

No matter where they live or how big they are, studies indicate that all Hanuman langurs make use of whatever food is available to them. For example, in the evergreen forest of Ramnagar, in southern Nepal, Hanumans adjust their culinary tastes with the three seasons: winter, spring and monsoon. During the monsoon, the monkeys gorge on fruits and young leaves. They also go off their predominantly vegetarian diet to slurp slow-moving, protein-rich caterpillars. During winter, they survive solely on the flowers and dry fruit of just one type of large, climbing liana. Come spring, the hungry monkeys will devour just about any plant they can get their furry little hands on.

With that kind of adaptability, the sky’s the limit—literally—when it comes to habitat. Hanuman langurs can be spotted on cold winter days huddling together with their ebony faces tilted toward the sun on rocky Himalayan outcroppings as high as 14,000 feet. "The first time I saw one in the mountains," remembers Hrdy, "I couldn’t believe it. I thought it was a statue." Others trekking the Himalayas have occasionally mistaken the thick gray coat of a Hanuman langur for the fabled Yeti.

At such high elevations, food sources are scarce even when they are abundant elsewhere. So the hearty monkeys are often forced to subsist for long periods of time solely on bark and mature leaves that have lost most of their nutritional punch. During summer and fall, mountain langurs are also known to supplement their diets with other, cultivated food sources, including wheat, barley and potatoes. And that can get them in big trouble.

Hanuman langurs may be sacred to devout Hindus, "but villages will make pacts to get rid of crop-raiding monkeys," says Hrdy. In fact, the first phrase she learned upon arriving in India to study the langurs was "please stop throwing stones at the monkeys." Crop raiding is especially worrisome to conservationists. Though the Hanuman langur is not yet listed as an endangered species, its future could be bleak thanks to many of the common threats—habitat destruction, development, human encroachment—plaguing primates worldwide. And it’s not likely that farmers will stop persecuting pilfering monkeys any time soon. For people living at high elevations, food is survival, says Koenig. "These people are very poor." When it comes down to a choice between human lives and monkeys, humans inevitably prevail. "In the future, I doubt these monkeys have a very good chance of surviving in their natural habitat," Koenig explains. "But you will probably still see them in cities where they are provisioned."

In the forests where Hanuman langurs do still persist today, the acrobatic animals spend the majority of their time in the treetops—a lifestyle facilitated by their anatomy. The name langur comes from the Sanskrit langulin, "having a long tail," and the Hanumans have longer tails than any other langurs—up to three feet or more. They depend on those tails as balancing rods that keep them aloft on high branches.

National Wildlife Magazine Image - Animal

Photo: © CYRIL RUOSO (BIOS/PETER ARNOLD INC.)

FRIEND OR FOE: For the most part, Hanuman langurs live a peaceful lifestyle. Troops while away the days foraging, keeping track of playful adolescents, mating and grooming. But when a bachelor male overtakes the leader of a harem, infants often become targets for murder. Studies suggest a new ruling male can increase his chances of siring offspring by killing the unweaned infants in a troop because females enter estrous when they stop nursing.

Arboreal living helps Hanumans avoid threatening predators, such as leopards, hyenas, wild dogs, pythons and tigers. According to Uma Ramakrishnan, a Connecticut-based scientist who has studied langur predator avoidance in the rain-soaked forests of India’s Kalakad-Mundanthurai Tiger Reserve, Hanuman langurs clump together in the trees and make a rumbling call, called a cackle bark, that sounds like explosive, hacking coughs: Aaaaccchhh! Ooooccchhhh! Scientists who study Asia’s leopards (relatives of Africa’s better-known spotted cats) have the luxury of being able to track the elusive felines by simply following the eerie sound of langur cackle barks ricocheting through a forest.

In the event that a leopard does dare to mount a tree and grab a langur, chances are it won’t get a very important one. The monkeys adhere to a social pecking order that applies even when they are sleeping, says Ramakrishnan. The highest-ranking male naps at the top of a "sleeping tree," far from the grasp of predators (India doesn’t have the monkey-snatching raptors that Africa does). Females with babies sit just below the male, followed by younger females. The riskiest posts at the base of the tree usually fall to the adolescent males. "Subadult males are eventually kicked out of a troop—a behavioral adaptation to avoid inbreeding," Ramakrishnan explains. "They will join other troops or form a group of bachelor males."

Nomadic bands of bachelors can range in size from just a few individuals to more than 60. Other langur societies contain as many as a hundred animals centered around a tightly knit core of females and their offspring, which are accompanied by one or more dominant adult males. The females are closely related and stick together in a single territory for their entire lives. While the males’ time with the troop is short-lived—on the average, only two years.

"The bachelors roam around testing the males with harems," says Koenig. And when they find a weakness, they often attempt a takeover. With threatening, open mouths, the 40-pound bachelors rush into the troop, grinding their teeth and whooping. When the alpha male responds to such a call to combat, a fierce battle ensues. The males spar with razor sharp teeth, and infants cling to their mother’s chests as the females chase the invaders, slapping at them with long, stinging arms. The war ends when the bachelors either retreat or drive off the alpha male, seizing command of the troop. Shortly after such a victory, the strongest member of the bachelor group often evicts his fellow comrades and gains full reign.

An occasional finale to such a coup d’état occurs when a succeeding male snatches his new troop’s unweaned infants one by one from their mothers’ clutches and sinks his canines into their skulls in a bloody act that has become known as one of nature’s most blatant examples of genetic perseverance: infanticide.

National Wildlife Magazine Image - Animal

Photo: © CYRIL RUOSO (BIOS/PETER ARNOLD INC.)

MOUNTAIN HIGH: From sea level to 14,000 feet, Hanuman langurs inhabit a wider array of habitats than any other primate in the world, say scientists. Against the snowy backdrop of the Himalayas (above), climbers have occasionally mistaken the gray furry monkey for the fabled Yeti. But farmers know all too well the telltale footprint of a hungry group of langurs that have scoured their fields for fruits and vegetables on a risky, moonlit food raid.

The earliest documented report of infanticide among langurs dates back to the 1960s when Japanese scientists doing research in India witnessed for the first time an outsider successfully overthrowing a leader. Afterward, the victorious male bit six of the troop’s infants to death. The account shocked many scientists because it defied the accepted wisdom of the day: Only humans routinely murdered members of their own species.

Primatologists floundered for an explanation of the langur’s macabre behavior until the early 1970s when Sarah Hrdy suggested the episode and others like it were linked to Darwin’s theory of sexual selection, which states that males will compete for access to fertile females with the females choosing the best male. "Only in this instance," Hrdy explains, "infanticidal males were canceling the female’s last ‘choice’ and forcing her to choose him instead. The mother whose unweaned infant is killed becomes fertile again sooner than if she continues to nurse, increasing the new male’s chances of breeding with her. His attack on the infant is purposeful and goal orientated, as organized and focused as a shark’s."

In recent years, infanticide has been documented in a wide range of primate species, from baboons, macaques and howler monkeys to some of man’s closest relatives: chimpanzees and mountain gorillas. Genetic studies by Borries at the State University of New York–Stony Brook and others have further supported Hrdy’s theory of infanticide in langurs by revealing that murderous males rarely, if ever, make the mistake of killing their own "kids."

The females also seem to be evolving strategies for protecting their genetic progeny. Studies have shown they take advantage of a male’s reluctance to kill his own offspring by mating with a variety of outsiders in addition to the alpha male. "What from a male view looks like promiscuous behavior," says Hrdy, "is from a female’s view assiduously maternal."

Interestingly, all Hanuman females seem to exhibit some degree of maternal behavior, even when they are not carrying infants of their own. Reminiscent of God Hanuman’s valiant efforts to save his king’s bride, the females will fight fiercely to thwart the advances of infant-snatching males. Researchers are still trying to explain why the females are so loyal to their fellow troop mates, but some say the behavior is probably linked to kinship. A female may support her sisters, cousins and aunts with the expectation that when she needs help, they’ll be there—an "I’ll scratch your back if you scratch mine," sort of phenomenon. But what’s always shocking, says Koenig, is when a male succeeds in killing an infant, the females will turn right around and mate with him. "There are no ethics involved. The human concept of good versus evil does not exist in langur societies. Nature is not good or bad, it’s just nature."

Rene Ebersole is an associate editor of the National Wildlife Magazine.

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