The Orang-utan as an Indicator Species

The orang-utan – called “person of the forest” by local people and the “neglected ape” by many scientists - is one of our closest relatives; that is, we belong to the same taxonomic group, together with all great apes. Although this relatedness may not be a simple linear ancestry, human primates and the orang-utans have a common ancestor as recently as 10-12 million years ago (see Schwartz 1984 and 2004 for his reading of that relationship).

The ancestral orang-utans were larger and more sexually dimorphic (Zhao et al. 2009). They probably lived a less arboreal existence and were much more widely distributed than they are today. Fossil evidence shows that orang-utans once ranged from Borneo into mainland Indochina and China, as far north as present day Beijing (Zhao et al. 2009). Perhaps, some think, orang-utans were driven back into a more arboreal lifestyle by ground predators. Today, on Sumatra, predators of the orang-utan include the Sumatran tiger (Panthera tigris sumatrae) and the clouded leopard (Neofelis nebulosa), while on Borneo only the clouded leopard is present (Rijksen and Meijaard 1999). One interesting fact is that the orang-utan today is absent from all islands (and of course mainland areas) where leopards (Panthera pardus) occur. For example, while leopards occur on Java, orang-utans do not. The leopard is a very skilled predator, able to catch even arboreal primates (Karanth and Sunquist 1995; Sankar and Johnsingh 2002), however it is unknown if the leopard had a hand in the orang-utan's disappearance from the mainland and its absence from Java.

The disappearance of orang-utans from the mainland of China and Southeast Asia, and their resulting restriction to the islands of Borneo and Sumatra, was a gradual process that occurred over a roughly 10,000-year period. The difference between their decline then and now is that, today, their decline is very dramatic. Before the turn of the nineteenth to the twentieth century there were probably over 200,000 orang-utans in Borneo and Sumatra (Meijaard et al. 2010). In the first modern large-scale wave of destruction, hundreds and thousands of these orang-utans were shot by big game hunters, adventurers, plantation owners and especially scientists who shipped their carcasses back to European museums. Orang-utans have never really been able to recover from these killing sprees, partly because their populations were also increasingly fragmented as human populations pushed into their territory and denuded their forest homes at an ever-accelerating rate (Meijaard et al. 2010).

In 1980, there were estimated to be only 80,000 orang-utans left in the wild. By 1996, new estimates spoke of only 23,000 and, just a year later, it was thought that orang-utan populations had plummeted to about 15,000. The actual number of protected wild orang-utans (i.e. living in one of the national parks) is currently 4,000 (Rijksen and Meijaard, 1999). These population estimates refer to Sumatran and the Bornean orang-utans combined. However, these two geographically separate groups may represent two distinct subspecies, and Borneo's orang-utan population itself may consist of at least two more subspecies. Obviously, if overall population counts are divided into several distinct groups, orang-utan numbers per subspecies have reached critical numbers.

The fact that the orang-utan's habitat is shrinking is all the more cruel when we understand how resourceful and flexible orang-utans are. In everything they do, they are master generalists as humans are said to be (cf Meltzoff 1996). Moreover, they are perhaps the fastest of the great apes in problem solving (Lethmate 1982), have excellent memories, are superb imitators and very skilled trapeze artists. They are the largest mammal living in the canopy, and negotiating this habitat is said to require high cognitive abilities. The performance of orang-utans in the cognitive domain baffled early researchers because it was believed that ‘intelligence’ required many different social interactions (as gorillas and chimpanzees have but orang-utans do not) and extensive play in childhood (Baldwin 1986) - again, something that was known to occur amongst other great apes but not orang-utans. Orang-utans will use boats, make fires, learn to play the guitar, wash clothes and do whatever they have seen humans do, simply by observation without being taught (Russon and Galdikas 1995). In the wild, infants and juveniles often imitate their mother’s behaviour. (Call 1999), They learn to use tools with amazing speed (Bard 1993; Visalberghi et al. 1995; Russon 1998) and also make some in their natural habitat (van Schaik et al. 1996; Fox et al. 1999; Rogers and Kaplan 1994).

In some mental abilities, such as symbolic play, language comprehension and tool using, a five-year old orang-utan may perform at about the same level as a four-year old human child (Miles 1990). In addition, more recent studies have emphasised the capacity for social learning in great apes, including the orang-utan (see reviews in Whiten and Ham 1992; Tomasello and Call 1997, and papers in Heyes and Galef 1996). It is important here to emphasize that the orang-utan belongs to the group of apes capable of higher cognitive tasks, which were once considered the sole domain of humans (Call and Tomasello 1994 ab; Byrne 1995; Rogers and Kaplan 2004b).

Orang-utans seem well-adapted to their rainforest environment.  They obtain a large variety of food items (over 400 different kinds) in all levels of the forest, from the ground to the top of the canopy (Kanamori et al. 2010). They know where to find edible roots and extract these from the soil (Parker 1996), feed on berries fruiting on the ground or on stems, pick fruit at any height in a tree and consume leaves, nuts and even the bark of trees (Bastian et al. 2010). Apart from elephants, they are the only species that has managed to crack the sugar rich durian fruit. They obtain animal proteins from ants and other small insects, reptiles and eggs. Orang-utans may be semi-nomadic, if need be, or sedentary as circumstances require. Furthermore, they usually succeed in raising their offspring (unless poachers take them) (MacKinnon 1974; Kaplan and Rogers 2000).

So well adapted are orang-utans to their environment that they are now generally regarded as an "indicator species", i.e. one that serves as a barometer for the well-being of other rainforest species and for the general health of the whole rainforest. If orang-utan populations are declining, then it is generally safe to conclude that many other rainforest organisms are also in trouble.

History of Attitudes to the Asian Great Ape

Over the centuries, the orang-utan has fared rather badly at the hands of western nations, and in the minds of their peoples. Ironically, despite or because of Charles Darwin’s evolutionary theory, it was considered necessary to delineate humans sharply from animals (Kaplan and Rogers 2004). This was true particularly of apes which, according to Darwin, had become our evolutionary relatives. In the minds of many, this perceived travesty demanded that the human condition be strenuously defended as unique and superior. Claims of a natural link between great apes like the orang-utan and humans were therefore discredited by constantly pointing to evolutionary 'disjunctions' (i.e., we can do things they cannot do), or by discarding pantheistic ideas. The latter refers to a theological position in the Judaic-Christian tradition which, broadly speaking, argues that all living things are God's creation, i.e. have a divine spark and are thus capable of wisdom, altruism, love and perhaps even moral judgement. The processes of the nineteenth century changed all this dramatically. Once divested of intrinsic positive values (i.e., ‘the divine spark’), assessment of animals switched from wise, gentle and loving to dumb, dirty and lazy. The latter description was particularly used for orang-utans (Kaplan and Rogers 1994, 1995).

We have a number of records from the early nineteenth century onwards that demonstrate the general negative tenor well. For instance, in 1838, a naturalist called Rennie condemned orang-utans as slovenly and useless creatures:

"Their deportment is grave and melancholy, their disposition apathetic, their motions slow and heavy, and their habits so sluggish and lazy, that it is only the cravings of appetite, or the approach of imminent danger, that can rouse them from their habitual lethargy, or force them to active exertion." (cit.Yerkes and Yerkes,1945).

Travelling accounts of nineteenth century adventurers and scientists claimed to attest to the general ‘uselessness’ of orang-utans and their undesirable nature. Stories were told of orang-utan males who abducted fragile English ladies and raped them in trees. The orang-utan was said to grow too large and strong for a pet, and to be of only limited use as a domestic helper (an 1892 record purports to ‘employ’ an orang-utan as a ‘domestic’, cf. Yerkes & Yerkes, 1945). In addition, the orang-utan was said to compare poorly in entertainment value to the chimpanzee and, overall, was not perceived as having any immediate medical or research value. It was further alleged that the orang-utan was difficult to observe, boring to watch because of its 'sluggish' behaviour and difficult to keep confined.

These sentiments were still echoed in the twentieth century. For instance, a scientific paper by Sonntag (1924) argued that, “the orang is the least interesting of the apes. It lacks the grace and agility of the gibbon, the intelligence of the chimpanzee and the brutality of the gorilla. (cit. Yerkes and Yerkes, 1945)." Even in the 1960s it was claimed that there was “nothing very spectacular about them (Reynolds, 1967).” The orang-utan was thought to be less suitable for experiments (Drescher and Trendelenburg, 1927; Yerkes, 1929), less capable of problem-solving (Köhler, 1926; see also Kaplan and Rogers 1995) and less skilled in manipulating than other apes, especially the chimpanzee.

Greater interest in and a more positive regard for orang-utans slowly emerged in the 1960s and 1970s, and today the orang-utan is one primate high on the list for documentary films and magazine articles. There is now a new school of thought that argues that apes, precisely for their relatedness to humans, deserve more respect, more freedom and a better future than they are likely to get if present practices continue (Cavalieri and Singer 1993; Sunstein and Nussbaum 2004). These changes of attitude notwithstanding, the orang-utan now belongs to the ever-growing list of endangered species (Cocks 2002).

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