Orangutans: Wizards of the Rain Forest

Orangutans: Wizards of the Rain Forest

by Anne Russon

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Product Details

ISBN-13: 9781552979983
Publisher: Firefly Books, Limited
Publication date: 08/07/2004
Edition description: Revised edition
Pages: 240
Product dimensions: 8.00(w) x 10.00(h) x (d)

About the Author

Anne E. Russon is an Associate Professor in the Department of Psychology at York University in Toronto. She has been studying intelligence and learning in orangutans in Indonesian Borneo since 1989. She co-edited a book on great ape intelligence, Reading into Thought: The Minds of the Great Apes.


Read an Excerpt

Orangutans 101

I chose to study orangutans because most researchers in the field of great ape intelligence had ignored them, despite hints that beneath their sluggish exteriors they are exceptionally thoughtful. But if there wasn't much information on their intelligence, there was plenty on other facets of their adaptation; efforts to study wild orangutans began in the late 1950s. The job turns out to have its easy side. Orangutans spend their time slowly and serenely meandering through the treetops, just minding their own business. Unfortunately they do it in the almost inaccessible, swamp-logged, leech-laden tropical rainforests of Borneo and Sumatra. They also, on occasion, chase researchers out of their forests. It would take humans as obstinate as orangutans themselves to brave the discomfort of that environment to study them. Fortunately, there have been some. They now number in the dozens.

The great red Buddha

Orangutans signature feature has to be their red-orange color. Surprisingly, that is also one of the main reasons they are hard to study, because it makes them especially difficult to find. Finding a wild orangutan makes finding a needle in a haystack look like a kindergarten task in comparison. As a hint of how hard it can be, in the late 1950s George Schaller logged only 5.75 hours of direct observation of wild orangutans, after months of work. Part of the difficulty is that orangutans come quietly, in ones and twos, way up in the canopy, half hidden in foliage. On top of that, believe it or not, their orange color lets them vanish. Many researchers, myself now included, can attest to watching an orangutan disappear right before their eyes. The explanation lies in the way sunlight penetrates the forest. Because the rainforest is so deep and dense, most sunlight that filters through the canopy does so by bouncing off vegetation. Vegetation reflects green light
— the color we see — but absorbs red and orange. By the time sunlight has bounced down through the canopy it has been robbed of its ability to register reds and oranges. In the midst of forest vegetation or on the forest floor, orangutans become large, dull brown lumps, just like the dead wood littered everywhere.

Beyond color, orangutans' most prominent feature is size. Like all great apes, orangutans are exceedingly large — in scientific terms, they come under the heading of megafauna. Largest by far are adult males, reaching 1.25 meters tall and over 100 kilograms in weight. Their strength is legendary, reputedly seven times as great as a man's. So much larger are adult males than other orangutans that the Iban Dayak people of north Borneo call them a separate species of orangutan, the biggest of three. The other two "species" are the middle-sized and the small (the Dayaks say they never get large). The middle-sized ones would be adult females and near-adult males and females, who are close to a meter tall and 35 to 50 kilograms, about half the adult male weight. Little ones would of course be youngsters. They weigh only 1.5 to 2 kilograms at birth and remain under about 25 kilograms for six or seven years. In this phase they grow so slowly, they could seem permanently small. Their growth spurts at adolescence, at least in males, but then they change so much as to be virtually unrecognizable.

Adult males also differ from other orangutans in having cheek pads. a great drooping throat pouch, long, shaggy hair that can look like dreadlocks, and a distinctive "long call." Cheek pads are subcutaneous accumulations of fibrous tissue between eyes and ears that give their faces the look of giant pieplates or blinkered horses. Peter Rodman and John Mitani have suggested they may help aim the male's long call so that it travels farther, and their visual impact — massive size — makes a very convincing threat. These features are likely important to orangutans' mating system, in which adult males compete for access to a precious group of females who can carry their offspring.

Orangutans, like all great apes, are designed for life in the trees suspended below branches, so their arms are longer than their legs and their shoulders wider than their hips. Orangutans are the only great apes to embrace this modus operandi close to full time, travelling as well as sleeping and eating in the trees, so they have exceptionally narrow, elongated arms and hook-like hands and feet for grasping branches. The other great apes, all from Africa, tend to travel on the ground by walking quadrupedally on their knuckles. When orangutans travel terrestrially, they walk either upright or quadrupedally on their fists.

Orangutans are exceptionally long-lived. The current estimate of their lifespan is thirty-five to forty years but researchers now know wild adults in their late forties at least and captives who have reached sixty. Orangutans have the longest immaturity of all the great apes, nine to twelve years. Their immaturity has three stages of roughly equal length — infant, juvenile, and adolescent — paced by birth, weaning, puberty, and sexual maturity. Females are deemed adult with the birth of their first infant, around fourteen to sixteen years, and males with the emergence of full adult regalia — cheek pads, throat pouch, and long call — as late as nineteen or twenty years. Males show an unusually prominent two-stage maturation, with adulthood preceded by a distinctive and indeterminate subadulthood stage. Male subadulthood usually starts at about ten years of age and lasts until about fifteen, but may continue until nineteen or twenty or even, very rarely, until thirty-five or forty

Reproduction, correspondingly, is exceedingly slow. Orangutan females' estrus cycles average thirty (29-32) days, their pregnancies are just under nine months long (230-260 days), and they give birth to a single infant at a time. In all this they are very like human females, except for the fact that they bear an offspring only once every eight to ten years. This may contribute to the males' fierce competition for females. It also makes orangutans extremely fragile as a species: they reproduce so slowly that losses take decades, even centuries, to replace.

Islands of the apes

Orangutans range today only on the islands of Borneo and Sumatra. They are not spread everywhere on the two islands. Their diet, primarily fruit, makes for a marked preference for lowland alluvial and peatswamp forest habitat close to waterways. The best orangutan habitat is near coasts and rivers, because farther inland elevation rises and other forests predominate. Permanent orangutan populations are rarely found above 500 meters of elevation.
Those ranging higher probably migrate to lower elevations for food for some periods of the year.

Orangutans' island distribution has led biologists to recognize two subspecies. perhaps even two species, Bornean and Sumatran. Sumatran orangutans tend to have red-orange hair, often whitish around the mouth and abdomen; Borneans tend to be darker, sometimes almost chocolate. Bornean adult males tend to have more robust bodies than Sumatrans as well as larger, differently shaped cheek pads, while Sumatran males have better beards. Sumatrans seem to be more arboreal and somewhat more social than Borneans, who have a bit of a reputation for turning into grumpy old men (and women).

The variability may be even greater. Borneo is the third largest island in the world, and is divided by high mountain ranges and wide rivers that, for orangutans. are as old and impassable as the straits dividing Borneo and Sumatra. Corresponding to Borneo's major geographical regions — east, northwest, and southwest — there may be three types of Bornean orangutan. It seems to be the easterners that tend to chocolate coloration. The southwesterners, in the region closest to Sumatra, look much like typical Sumatrans, although there may be several types of Sumatran orangutan too. Herman Rijksen detected a robust Sumatran type with lightish skin, orange-red hair, heavy build, and stubby hands and

Table of Contents

Introduction

Aristotle's Rubicon

  • Gifts from the Greeks
  • Baggage from the past
  • Great apes on the Western stage
  • Ape Nature
  • Bornean views
  • Looking past belief

Orangutans 101

  • The great red Buddha
  • Islands of the apes
  • Being orangutan
  • Thinking on the wild side
  • Personal pickle

The World According to Camp Leakey

  • Bridging two worlds
    • Food
    • Nest and Rest
    • Travel
    • Sociality and Sexuality

The Sorcerer's Red Apprentice

  • Mechanical genius
  • Plans
  • Abilities in concert

Trouble in Eden

Wanariset: The New Rehabilitation

  • Close-up on captivity
  • Socialization
  • Enrichment

Tropical Rainforest Homes

  • Reaching for the sun
  • The seasons
  • Interdependencies
  • Arboreality reconsidered
  • Acquiring the expertise

Lord of the Flies

  • The players
  • Roughing it in the bush
  • The food's the thing
  • What's eating Paul
  • Encounter
  • Tools for food
  • Food for imitation
  • Planning for food
  • Deceptions
  • Is there life beyond food?

Release Me

  • Settling in
  • Taking stock of forest skill

The Mirror Crack'd

  • Inferno

If Not Now, When?

  • Destruction

Organizations Concerned with Orangutan Welfare
Bibliography
Index


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