The Holy Hanuman

"Au! Au!" The man pants heavily, dragging a sizeable bag uphill. His calls, however, do not express pain but devotion. "Au!" means "Come!" in Hindi. And come they do: Dozens of greyhound-sized creatures in silvery coats emerge from shady crevices in the sandstone cliffs, appear from behind bushes of spiky Euphorbia, climb out of the canopy of Acacia trees, jump from the roof of a temple. "Le! Le! - Take! Take!" The man opens his bag and places potatoes and aubergines in the open palms that surround him.

The scene plays in Jodhpur, a town in North India, but is re-enacted all over the subcontinent where devoted Hindus serve a favourite deity: Hanuman. Biologists call the God's incarnations variedly Gray langurs, Hanuman langurs or Indian langurs and place them as either Semnopithecus entellus or Presbytis entellus in a genus of Colobine primates, a subunit of Old World Monkeys.

Hindu believers pay reverence to langurs because a monkey named Hanuman is the key actor in India's national epic. The "Ramayana" praises God Rama and his beautiful spouse Sita. Alas, the demon king abducts Sita to the island of Lanka. Hanuman masterminds Sita's rescue by commanding a victorious army of monkeys. Half way through the saga, demon guards capture Hanuman and wrap his tail with oil-soaked cloths before setting it on fire. The noble monkey escapes and drags his torched tail across the roofs of Lanka, burning the villain's residence to ashes.

This tale explain why langur monkeys are favourites amongst the pantheon of holy animals roaming India. The Sanskrit word "langulin" translates as "having a long tail", a connection also seemingly preserved in the English "long". It's certainly a fitting name, given that langur tails may exceed head-rump length by 150 percent and can reach 112 cm, a record for any primate. These appendages help navigate jumps of up to eight meters - a useful device not only above the rooftops of Lanka. More importantly, the charcoal black feet, hands and faces of India's temple monkeys are testimony to their heroic ancestor Hanuman, who suffered burns while setting the demon city ablaze.

Elaborate funeral rites may be bestowed on dead monkeys. Devoted Hindus will adorn the body with garlands and sprinkles of beautifying ochre. The deceased is placed on a bier, not reclined, however, but in a sitting position, legs crossed. Such honour is reserved for senior persons who will therefore make their last journey upright. Most monkeys are buried - as is customary for human children and animals - but some Hanumans are cremated, thus tearing down the traditional boundary between humans and animals.

The interrelatedness of all life-forms is also the grand theme of the scientific approach to the lives and deaths of Hanuman langurs. Nowhere have they been observed in greater detail than around Jodhpur in the sunny and dry state of Rajasthan at the edge of the Tharr desert. Generations of researchers from India, Germany and the UK have chronicled the behavioural and reproductive pattern of langurs for the last 35 years, placing them amongst the best studied primates on earth.

Flexible Ecology and Sociality

Like good Hindus, langurs obey a rather strict vegetarian diet. There is the occasional munch of a locust or larvae, but the monkeys are really specialised to exploit hundreds of different plants. A chambered stomach, similar to ruminants, teems with bacteria that can process cellulose. This allows the digestion of large quantities of leaves, though langurs prefer shoots, blossoms, fruit and occasional snacks of gum that seeps from the bark of trees. The langurs spice their diet with small quantities of minerals since they regularly lick stones or eat earth and charcoal (including residuals from funeral grounds). This may help to buffer against toxins which plants manufacture to deter herbivores. However, almost nothing will put off langurs. They can even tackle strychnoid plants which instantly kill same-sized animals such as hardy goats. Most of the langur's natural food does not provide readily available calories and forces the animals to take long naps to digest their bulky meals.

Thanks to their unfussy dietary requirements, Hanuman langurs can be found in many different environments, allowing them the largest geographical distribution of any of the 230 or so non-human primates. They dwell from the Himalayan mountains through the semi-arid zones of Rajasthan to the cultivated plains along the mighty streams; they are as at home in the urban environments of countless cities in the Indian peninsula as in the tropical forests of Sri Lanka - ancient battle-place of the "Ramayana". Only one other primate surpasses such tremendous ecological adaptability: Homo sapiens.

Hanuman langurs share another feature with humans which also reflects their ubiquitous status in the primate world: a considerable social flexibility. In some areas, langurs form troops with multiple adult males and females. Elsewhere, a single male lives with multiple females in a so-called harem while surplus males join bachelor bands. At yet again other places, varying proportions of one-male versus multi-male troops are found simultaneously.

Scientists have wondered, how males can monopolise females in some areas whereas they cannot prevent their peers from mingling with the fairer sex at other sites. This riddle is far from solved although the long-term study at Jodhpur provides some tentative answers.

The semi-arid habitat around Jodhpur is home to a geographically isolated langur population with a particularly rigid one-male structure. In the mid 1990s, researchers counted 1300 monkeys. Bachelors were found in 14 bands with an average of 12 members. In the 29 bisexual troops, harem holders enjoyed average tenures of 27 months amongst 14 females. The longest residence lasted seven years. The largest harem contained 35 females - a total of 83 langurs, if all immatures are included.

Tough Luck for Bachelors

Various factors provide harem holders with an edge over their male band competitors. Harems occupy small ranges in the vicinity of ponds or wells where local people can easily find them. Almost all troops receive massive donations of vegetables, fruit and wheat cakes. This allows a harem holder to gulp down large amounts of food quickly and devote much of his time to sentinel activity. Additionally, the open landscape with its scattered bushes and thin tree cover makes it difficult for bachelors to sneak up to the females. However, chances to reproduce are slim even if a bachelor could successfully invade a troop. The ample food supply allows females to give birth year round. Consequently, only one or two females will be fertile on any given day in a particular troop - and a harem resident can easily concentrate to mate-guard those.

Bachelors are also severely disadvantaged because for them, foraging is a challenging task. Harems occupy the good spots, forcing bands to criss-cross large areas in search of edible vegetation and water. Feeders will rarely locate these nomads. Moreover, it is difficult for the males to become familiar with their extensive ranges, which contain many hazards. Bachelors, already weakened by food and water stress, are therefore prone to fatal falls out of trees, car accidents, electrocution from power lines or predation by packs of feral dogs.

Males have little choice but to trade the relative comfort and security of their natal troops with the perils of bachelor life when a new harem holder takes over. Typically, cohorts of juvenile siblings are ousted together - often together with their defeated father. However, these closely knit units of relatives will quickly thin out - given the risky bachelor life - and brothers hardly ever mature together to become prime males and thus contenders for a harem. One would otherwise expect that brothers would join forces, defeat a harem holder and share the females - as happens sometimes in lions. Such cooperation is virtually non-existent at Jodhpur. Bachelors will jointly invade a female troop, but only the highest ranking band member may challenge the current resident in an all-out fight.

Why are males willing to follow a high-ranking band fellow into battle at all, if he will turn against them as soon as he establishes himself as the new resident amongst the females? Bachelors seem to benefit from band life primarily because they find safety in numbers: external dangers such as preventive attacks by harem holders or ambushes by predators are diluted.

Escape From the Seraglio

The analysis of the one-male system at Jodhpur allows some predictions about the conditions prevailing at sites where multiple males live with the females. For example, a lack of provisioning by local people and strong climatic seasonality should lead to a relatively strict mating period. To guard multiple fertile females is very difficult for a single male, however strong. A densely forested environment will additionally hamper efforts to monopolise females.

Finally, it would be expected that extra-troop male mortality is lower in areas less influenced by human activity. This would allow siblings to grow up together, paving the way for a joint residency in female troops. Reproductive competition amongst related males is relaxed. Full-brothers carry, on average, 50 percent of identical genes, and half-brothers 25 percent. Their reproduction will benefit a sibling too, since at least a proportion of copies of the shared genetic information is passed on.

A comparison of Jodhpur with sites in the Himalayas and elsewhere on the Indian subcontinent supports these predictions at least tentatively.

The Gruesome Logic of Infanticide

An account of langur life would be incomplete without highlighting a most infamous event: The killing of babies by new harem residents. At least half of all infants present during resident male changes at Jodhpur are attacked, and one third is bitten to death. A widely accepted theory maintains that a nursing female is less fertile and that the violent removal of her infant shortens the waiting time until a new male can sire his own offspring. The average female at Jodhpur gives birth to about 17 infants - and will see four of them killed by males.

Interestingly, females could all but wipe out incidences of infanticide if they synchronised their menstrual cycles. This would bring about multi-male-multi-female troops and thus increase the number of sexual partners per female. The corresponding confusion of paternity makes it less beneficial for males to kill infants since they would run the risk of killing own progeny. Various primate females from species including marmosets and humans are indeed able to synchronise their fertility through olfactory signals. Langurs at Jodhpur don't do this - probably because an increased number of males decreases the available food for females, thus lengthening the interval between births. Such conditions might lower the net reproduction per female more than will the presence of infanticidal males. In a way, females seem to choose the lesser of two evils.

The theory about the adaptive function of infanticide is not undisputed. However, some criticism is nourished by a romantic view of animals as the better humans. Many people, particularly in the Western world, see modern culture as the root-cause for the destruction which Homo sapiens inflicts on the environment and innocent members of the own species. A hope of salvation is attached to crusades that proclaim "Back to Nature!" Sadly, such ideas are incompatible with the notion that even holy animals may act entirely selfishly.

A Primatological Mega-Experiment

Scientists at Jodhpur have collected data on langurs in unsurpassed detail and quantity. Still, one might be tempted to downplay their relevance since the population is heavily influenced by humans. However, the focus of primate research has shifted from a rather static conception about alleged "species typical" traits to a more dynamic perspective that tries to encompass the whole spectrum of adaptive capabilities. A comparison: the daily schedule of Londoners is glaringly different from that of Arctic hunter-gatherers, highlighting the influence that varying environmental conditions exert on organisms with almost identical genetic make-up. It is therefore futile to ask which living conditions are more representative for humans. Similarly, the gigantic open-air experiment at Jodhpur may exaggerate certain behavioural features, but these reveal nevertheless parts of the social plasticity of langurs.

Flexible social and ecological responses are hallmarks of both humans and langurs. The reproductive performance of both species is correspondingly high. Jodhpur's human population has tripled since 1967 and stands now at roughly two million. Over the same period, the langur population has also exploded - from 836 to almost 2000 monkeys. The reason is simple: more people means more believers to serve more food to Hanuman's divine deputies.