By Rhett Butler   |  Last updated July 30, 2012
The incredible diversity of food sources and unique niches of the canopy trees support a wide variety of animal species. Animals often congregate around a flowering tree, which makes trees in this stage some of the best sites for viewing wildlife. In places like these, where food is abundant, animals set up territories, but since canopy leaf cover affects visual territorial displays, most animals rely on sound signals. Thus some of the loudest animals of the world are canopy dwellers. Many primates emit howls and screams, while birds use song to let other animals know that they are intruding on their space.

Common paths, often leading to fruiting trees, where many animals may pass in the course of the day are well-worn and often free of epiphytes; these form highways in the trees. Similarly, areas in the canopy free of vegetation form flight corridors used by numerous species, especially the birds of prey which often attack their prey from below. These flight paths are embedded in the memory of bats and birds.


Despite the huge abundance of canopy leaves, few mammals are properly equipped to eat them. Cellulose, the material of which cell walls are made, is difficult to digest, so leaf-eating animals must have large stomachs to hold their meal while it is being broken down. A large stomach is often accompanied by a large body which can be detrimental to canopy dwellers who depend on branches to support their weight. Similarly, very few birds specialize in leaf-eating because the extensive digestive system adds weight that hinders flight. Interestingly, more Old World mammal species, especially primates, rely heavily on leaves for the bulk of their diet, but few New World primates have the physiological adaptations to digest fibrous cellulose. Forest canopy mammals outfitted to feed on leaves include sloths, howler monkeys, orangutans, and chimpanzees.


Sloth, Peru 1995. The mother has been slaughtered and eaten, as will this individual once it reaches adequate size.

Pale-throated Three-toed Sloth (Bradypus tridactylus)
Pale-throated Three-toed Sloth (Bradypus tridactylus)

Panamanian Three-toed Sloth (Bradypus variegatus)
Sloths (pictures) are unique mammals highly adapted to life in the canopy. They belong to the Endentata (= "without teeth") order, although they do possess cheek teeth, and are endemic to Central and South America. There are six to seven species represented by two distinct groups: the three-toed sloth and the two-toed sloth. Three-toed sloths feed almost exclusively on cecropia leaves, while two-toed sloths live high in the canopy feeding on a wide variety of leaves and fruits. Three-toed sloths range from Honduras to Argentina and are known locally by natives as "Ai" for their shrill call. Two-toed sloths or "unau" inhabit forest areas from Nicaragua to Bolivia and northern Brazil. Both species are predominantly nocturnal. To facilitate water runoff, the hair of both species grows from the stomach to the back since sloths spend most of their time hanging from branches upside down. The slow movement and moist climate of the hair stimulates the growth of green algae in the fur of the sloth, giving it a greenish color which helps it camouflage from predators like the harpy eagle. Sloths are well evolved as a leaf-eating mammal with stomachs divided into many digestive compartments that contain cellulose-digesting bacteria. A low metabolic rate combined with minimum movement and 15 hours of daily sleep help the sloth conserve energy. Leaf-eaters in general must consume large quantities of their food to satisfy their nutritional requirements. Leaves may last up to one month in the sloth's intestines and feces and urine are passed about once a week when the sloth descends to the ground at habitual places.

The sloth's fur is an entire ecosystem of its own: one study found more than 950 beetles on a single sloth, living off the algae growing in its fur. The fur is also home to a certain species of moth which is dependent on the sloth's descent for its life cycle. When the sloth reaches the ground, the moth quickly lays its eggs in the sloth's dung and returns to the sloth's fur. After the eggs hatch and the caterpillars become moths, the moths, in some way or another, claim another sloth.

The routine descent of the sloth raises an interesting question—if sloths are so clumsy and slow on the ground why do they put themselves at risk to terrestrial predators when they could easily defecate from the trees? The answer lies in the intricacy of the rainforest ecosystem. By defecating at the base of their host cecropia tree, the sloth provides the tree with precious fertilizer, a rare but vital commodity in most rainforests.

Howler monkeys (pictures) are another New World canopy animal that relies heavily on leaves. Howler monkeys have earned the distinction of the loudest animal, according to the Guinness Book of World Records, with their raucous howls that can be heard clearly at distances over 10 miles away. This record is quite believable when a troop of noisy howler monkeys approaches. The male howler monkey, closely related to the spider monkey, is equipped with a special voice box which enables it to vocally defend its small territory without physical confrontation. Howler monkeys live in troops of 5-20 animals (average), in which females and juveniles make up the greatest percentage. These stocky, black primates, weighing up to 20 pounds (9 kg), are also known to eat leaves, although this species usually turns to canopy leaves only when fruits are in short supply.


The orangutan has become the symbol of the protest against unsustainable palm oil. The Sumatran orangutan, pictured here, is critically endangered, largely due to habitat loss. Photo by: Rhett A. Butler.
In the Old World, a few canopy primates turn to leaves. The orangutan, Asia's largest rainforest primate, and the third largest primate in the world, is one of these. The orangutan was once found throughout Asia, but is now limited to northern Borneo (the Borneo orangutan species) and Sumatra (the Sumatra orangutan species). Male specimens of the Sumatran form may reach 5 feet (1.6 m) and 400 pounds (180 kg) with an arm span exceeding 6.5 feet (2 m). The Borneo form is much smaller. Orangutans occupy the mid-strata of the forest canopy where they feed on leaves, fruits, and young shoots, and occasionally may take a bird egg or two. Orangutans are not social animals, but solitary creatures that do not form lasting pairs. Fascinatingly, the unsociable behavior of orangutans is not instinctive but learned. Mothers enforce a regime of strict separation by dragging youngsters away from each other and leaving them alone in the forest. Solitary behavior is of the utmost importance for survival in the rainforest where food trees are widely scattered. A pair or a group of slow-moving orangutans would find little more food than an individual, but have to divide it among more mouths. Orangutans share 98 percent of our genetic makeup and, like humans, participate in prolonged care for their young. Like humans each individual has a distinctive face. From birth, the orangutan undergoes variations in facial structure during the course of its lifetime: at birth its face is bare, juveniles are bearded, and adult males have skin pouches on their cheeks. Orangutans build sleeping nests, 16-80 feet (5-25 m) off the ground, each night and never return to an earlier nest.

Orangutans are highly threatened by the illegal trade in endangered species and widespread deforestation in Indonesia and Malaysia. Scientists estimate that of the remaining 45,000-60,000 orangutans in the wild, more than 1,000 are poached every year as pets or sources of bushmeat.

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Articles about orangutans

Eat like an orangutan to save rainforests

(11/30/2011) One doesn't have to be a scientist or a government official to help save the world's vanishing rainforests, one can also be a chef. World-renowned chef Andre Chiang has added a new item to his menu called Orangutan Salad, reports the Wall Street Journal, which he hopes will raise awareness for the endangered apes at his Singapore eatery, Restaurant Andre. The new salad gives restaurant-goers the chance to enjoy all the subtle, earthy tastes of a typical orangutan meal, including ferns, tree fungi, figs, berries, orchid leaves, and durian flowers.

Orangutans in Indonesian Borneo doomed to extinction?

(11/14/2011) A new study finds orangutans in Indonesian Borneo in unprotected areas are being killed at a rate faster than what population viability analysis considers sustainable. Conflict between orangutans and humans is worst in areas that have been fragmented and converted for timber, wood-pulp, and palm oil production, but hunting is occurring in relatively intact forest zones away from industrial development.

Teaching orangutans to be wild – orangutan rehabilitation

(12/15/2010) Michelle Desilets, Executive Director of the Orangutan Land Trust, spoke with Laurel Neme on her 'The WildLife' radio show and podcast about the process of rehabilitating orphaned orangutans and teaching them to be wild. This is the second in a two-part interview. The first part covered orangutan biology, habits and the interconnected threats, from the pet trade to habitat loss and expansion of oil palm plantations, facing these creatures. This second part focuses on what happens to surviving orangutans.

The problem-solving ape: what makes orangutans special and why they are threatened

(12/13/2010) Michelle Desilets, Executive Director of the Orangutan Land Trust, spoke with Laurel Neme on her “The WildLife” radio show and podcast about orangutans. In the first part of her interview, they discussed orangutan biology, habits and the interconnected threats, from the pet trade to habitat loss and expansion of oil palm plantations, facing these creatures. The second part covers the process of rehabilitating orangutans and teaching them to be wild.

Orangutans can survive in timber plantations, selectively logged forests

(09/23/2010) Selectively logged forests and timber plantations can serve as habitat for orangutans, suggesting that populations of the endangered ape may be more resilient than previously believed, reports research published in the journal PlosONE. The study, conducted by a team of researchers led by Erik Meijaard of Jakarta-based People and Nature Consulting International, found roughly equivalent population densities between natural forest areas and two pulp and paper plantation concessions in East Kalimantan, Indonesian Borneo.

Orangutan populations collapse in pristine forest areas

(08/12/2010) Orangutan encounter rates have fallen six-fold in Borneo over the past 150 years, report researchers writing in the journal PLoS One. Erik Meijaard, an ecologist with People and Nature Consulting International, and colleagues compared present-day encounter rates with collection rates from naturalists working in the mid-19th Century. They found orangutans are much rarer today even in pristine forest areas. The results suggest hunting is taking a toll on orangutan populations.

Indonesian people-not international donors or orangutan conservationists-will determine the ultimate fate of Indonesia's forests

(07/29/2010) Many of the environmental issues facing Indonesia are embodied in the plight of the orangutan, the red ape that inhabits the islands of Borneo and Sumatra. Orangutan populations have plummeted over the past century, a result of hunting, habitat loss, the pet trade, and human-ape conflict. Accordingly, governments, charities, and concerned individuals have ploughed tens of millions of dollars into orangutan conservation, but have little to show in terms of slowing or reversing the decline. The same can be said about forest conservation in Indonesia: while massive amounts of money have been put toward protecting and sustainable using forests, the sum is dwarfed by the returns from converting forests into timber, rice, paper, and palm oil. So orangutans—and forests—continue to lose out to economic development, at least as conventionally pursued. Poor governance means that even when well-intentioned measures are in place, they are often undermined by corruption, apathy, or poorly-designed policies. So is there a future for Indonesia's red apes and their forest home? Erik Meijaard, an ecologist who has worked in Indonesia since 1993 and is considered a world authority on orangutan populations, is cautiously optimistic, although he sees no 'silver bullet' solutions.

Why we are failing orangutans

(03/01/2010) It is no secret that orangutans are threatened with extinction because their rain forests are being destroyed at an alarming rate. Ten years ago, Shawn Thompson, a writer, former journalist and university professor, set out to chronicle the threat to orangutans in a book released in March 2010. The book is called The Intimate Ape: Orangutans and the Secret Life of a Vanishing Species. The book spends most of the time talking about the nature of orangutans and the relationships between orangutans and people. But the ultimate underlying message is there about the source of the peril to orangutans and the solution. Thompson says that the problem of saving orangutans has to do with communications and human nature.

Orangutans vs palm oil in Malaysia: setting the record straight

(01/16/2010) The Malaysian palm oil industry has been broadly accused of contributing to the dramatic decline in orangutan populations in Sabah, a state in northern Borneo, over the past 30 years. The industry has staunchly denied these charges and responded with marketing campaigns claiming the opposite: that oil palm plantations can support and nourish the great red apes. The issue came to a head last October at the Orangutan Colloquium held in Kota Kinabalu. There, confronted by orangutan biologists, the palm oil industry pledged to support restoring forest corridors along rivers in order to help facilitate movement of orangutans between remaining forest reserves across seas of oil palm plantations. Attending NGOs agreed that they would need to work with industry to find a balance that would allow the ongoing survival of orangutans in the wild. Nevertheless the conference was still marked by much of the same rhetoric that has characterized most of these meetings — chief palm oil industry officials again made dubious claims about the environmental stewardship of the industry. However this time there was at least acknowledgment that palm oil needs to play an active role in conservation.

Palm oil both a leading threat to orangutans and a key source of jobs in Sumatra

(09/24/2009) Of the world's two species of orangutan, a great ape that shares 96 percent of man's genetic makeup, the Sumatran orangutan is considerably more endangered than its cousin in Borneo. Today there are believed to be fewer than 7,000 Sumatran orangutans in the wild, a consequence of the wildlife trade, hunting, and accelerating destruction of their native forest habitat by loggers, small-scale farmers, and agribusiness. Gunung Leuser National Park in North Sumatra is one of the last strongholds for the species, serving as a refuge among paper pulp concessions and rubber and oil palm plantations. While orangutans are relatively well protected in areas around tourist centers, they are affected by poorly regulated interactions with tourists, which have increased the risk of disease and resulted in high mortality rates among infants near tourist centers like Bukit Lawang. Further, orangutans that range outside the park or live in remote areas or on its margins face conflicts with developers, including loggers, who may or may not know about the existence of the park, and plantation workers, who may kill any orangutans they encounter in the fields. Working to improve the fate of orangutans that find their way into plantations and unprotected community areas is the Orangutan Information Center (OIC), a local NGO that collaborates with the Sumatran Orangutan Society (SOS).

Rehabilitation not enough to solve orangutan crisis in Indonesia

(08/20/2009) A baby orangutan ambles across the grass at the Borneo Orangutan Survival Foundation’s Nyaru Menteng rehabilitation center in Central Kalimantan, in the heart of Indonesian Borneo. The ape pauses, picks up a stick and makes his way over to a plastic log, lined with small holes. Breaking the stick in two, he pokes one end into a hole in an effort to extract honey that has been deposited by a conservation worker. His expression shows the tool’s use has been fruitful. But he is not alone. To his right another orangutan has turned half a coconut shell into a helmet, two others wrestle on the lawn, and another youngster scales a papaya tree. There are dozens of orangutans, all of which are about the same age. Just outside the compound, dozens of younger orangutans are getting climbing lessons from the Borneo Orangutan Survival Foundation (BOS) staff, while still younger orangutans are being fed milk from bottles in a nearby nursery. Still more orangutans—teenagers and adults—can be found on “Orangutan Island” beyond the center’s main grounds. Meanwhile several recently wild orangutans sit in cages. This is a waiting game. BOS hopes to eventually release all of these orangutans back into their natural habitat—the majestic rainforests and swampy peatlands of Central Kalimantan, on the island of Borneo. But for many, this is a fate that may never be realized.

Orangutan guerrillas fight palm oil in Borneo

(06/01/2009) Despite worldwide attention and concern, prime orangutan habitat across Sumatra and Borneo continues to be destroyed by loggers and palm oil developers, resulting in the death of up to 3,000 orangutans per year (of a population less than 50,000). Conservation groups like Borneo Orangutan Survival report rescuing record numbers of infant orangutans from oil palm plantations, which are now a far bigger source of orphaned orangutans than the illicit pet trade. The volume of orangutans entering care centers is such that these facilities are running out of room for rescued apes, with translocated individuals sometimes waiting several months until suitable forest is found for reintroduction. Even then they aren't safe; in recent months loggers have started clearing two important reintroduction sites (forests near Bukit Tigapuluh National Park in Sumatra and Mawas in Central Kalimantan). Meanwhile across half a dozen rehabilitation centers in Malaysia and Indonesia, more than 1,000 baby orangutans—their mothers killed by oil palm plantation workers or in the process of forest clearing—are being trained by humans for hopeful reintroduction into the wild, assuming secure habitat can be found. Dismayed by the rising orangutan toll, a grassroots organization in Central Kalimantan is fighting back. Led by Hardi Baktiantoro, the Center for Orangutan Protection (COP) has mounted a guerrilla-style campaign against companies that are destroying orangutan habitat in Kalimantan, the Indonesian part of Borneo.

Orangutan populations drop due to logging, expansion for palm oil

(07/03/2008) Orangutan populations have fallen sharply on the two islands where they still live, reports a new study published in the journal Oryx.

Orangutan should become symbol of palm-oil opposition

(01/02/2008) In a letter published today in Nature, Oscar Venter, Erik Meijaard and Kerrie Wilson argue that proposals for conservation groups to purchase and run oil palm plantations for the purpose of generating funds for forest protection are unlikely to be successful. The concept was originally put forth by Lian Pin Koh and David S. Wilcove in a 2007 Nature article.

Saving Orangutans in Borneo

(05/24/2006) A look at conservation efforts in Kalimantan, on the island of Borneo. I'm in Tanjung Puting National Park in southern Kalimantan on the island of Borneo. At 400,000 hectares (988,000 acres) Tanjung Puting is the largest protected expanse of coastal tropical heath and peat swamp forest in southeast Asia. It's also one of the biggest remaining habitats for the critically endangered orangutan, the population of which has been great diminished in recent years due to habitat destruction and poaching. And orangutans have become the focus of a much wider effort to save Borneo's natural environment. We are headed to Campy Leakey, named for the renowned Kenyan paleontologist Louis Leakey. Here lies the center of the Orangutan Research conservation Project. Established by Birute Mary Galdikas, a preeminent primatologist and founder of the Orangutan Foundation International (OFI), the project seeks to support the conservation and understanding of the orangutan and its rain forest habitat while rehabilitating ex-captive individuals. The Orangutan Research conservation Project is the public face of orangutan conservation in this part of Kalimantan, the Indonesia-controlled part of Borneo. Borneo, the third largest island in the world, was once home to some of the world's most majestic, and forbidding forests. With swampy coastal areas fringed by mangrove forests and a mountainous interior, much of the terrain was virtually impassable and unexplored. Headhunters ruled the remote parts of the island until a century ago.

News feed for orangutans

Chimpanzees (pictures | news), genetically, the closest living relation to man, are also leaf eaters, although they also feed on shoots, seeds, bark, fruits, and (less frequently) insects, fish, reptiles, and small mammals. Chimpanzees are highly threatened in their native West and Central Africa by destruction of habitat and hunting as a source of bush meat. Chimpanzees, up to 5.5 feet (1.7 m) when erect, are strong animals that dwell both arboreally and terrestrially.

Adult male orangutan in Sumatra, Indonesia
Adult male orangutan in Sumatra, Indonesia. Click image for more photos of orangutans. (Photo by R. Butler)

Review questions:

  • How do animals communicate in the canopy?
  • Why do relatively few animals eat leaves as the staple of their diet?
  • Where does the orangutan live and why is it endangered?

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