AJP 335
American Journal of Primatology 43:159–165 (1997)
BRIEF REPORTS
Meat-Eating by Adult Female Sumatran Orangutans
(Pongo pygmæus abelii)
SRI SUCI UTAMI,1,2,3* AND JAN A.R.A.M. VAN HOOFF3
1
Fakultas Biologi, Universitas Nasional, Jakarta, Indonesia
2
Ketambe Research Centre, Gn. Leuser National Park, Aceh Tenggara, Indonesia
3
Ethologie en Socio-ecologie, Universiteit Utrecht, Utrecht, The Netherlands
Information about meat-eating behavior by wild orangutans (Pongo
pygmæus) is scant. The first article about such a case dates from 1981.
Since 1989, seven incidents of adult female Sumatran orangutans eating
slow lorises (Nycticebus coucang) have been witnessed. Three females
from two study sites were involved. In three cases the females were
seen catching the prey. There are too few cases to conclude whether
this behavior is typically female. Am. J. Primatol. 43:159–165, 1997.
© 1997 Wiley-Liss, Inc.
Key words: Meat eating; Pongo pygmæus; Nycticebus coucang
INTRODUCTION
Most primates are considered to be herbivores, frugivores, insectivores, or a
combination of these. Carnivory, the eating of meat of larger tetrapod animals,
has been reported so far only for a few species in the wild. It has been observed,
for example, in different baboon species, Papio spp. [Kummer, 1968; Altmann
and Altmann, 1970; Harding, 1973, 1975; Strum, 1975, 1981; McKee, 1992], in a
few other catarrhine species [blue monkey, Cercopithecus mitis: Butynski 1982;
vervet monkey, Cercopithecus aethiops: Fairbanks, 1984; stumptail macaque,
Macaca arctoides: Estrada & Estrada, 1977; Estrada et al., 1978], in different
populations of chimpanzees [Pan troglodytes; Teleki, 1973; Boesch & Boesch, 1989;
Boesch, 1994a,b; Uehara et al., 1992; Huffman & Kalunde, 1993] in the bonobo,
Pan paniscus [Ihobe, 1992], and possibly in the gorilla, Gorilla gorilla [Fossey,
1983], and a gibbon, Hylobates lar [Newkirk, 1973].
For example, in chimpanzees the diet consists primarily of fruits, with prey
comprising a minor part [Teleki, 1973; Goodall, 1986; Stanford et al., 1994a,b].
Chimpanzees eat a variety of animals. They consume invertebrates, such as ants
and termites, often with the aid of tools [Goodall, 1968; Teleki, 1973; McGrew,
1974, 1979]. Occasionally, they also hunt vertebrates, chiefly monkeys, and small
ungulates [Nishida and Uehara, 1983; Hasegawa et al., 1983; Boesch and Boesch,
1989], and they may even eat slain conspecifics [Suzuki, 1971; Goodall, 1977;
Nishida & Kawanaka, 1985; Hamai et al., 1992].
*Correspondence to: Sri Suci Utami, Ethologie en Socio-ecologie, Universiteit Utrecht, Pb. 80.086,
3508 TB Utrecht, The Netherlands. Email: [email protected].
Received for publication 10 December 1996; revision accepted 18 April 1997.
© 1997 Wiley-Liss, Inc.
160 / Utami and van Hooff
Until recently there was only one report on meat-eating in orangutans.
Sugardjito and Nurhuda [1981] described a wild adolescent female orangutan,
named Sina, at Ketambe found to be eating a gibbon. Since 1989 we have seen
six cases of meat-eating by orangutans during our socioecological field work in
Ketambe, Southeast Aceh. Recently the same phenomenon has been observed in
Suaq Balimbiang, South Aceh, Sumatra [van Schaik, personal communication].
The Ketambe population has been studied since 1971, first by Rijksen and subsequently by Schürmann, Sugardjito, Suharto, and Tatang Mitra Setia. Individuals
of this population have been observed for at least 20,000 h during the past 20 years.
Apart from the report of Sugardjito and Nurhuda, no meat-eating has been seen.
We report these cases, since knowledge of the conditions under which meateating and hunting occur in our nearest relatives is important for understanding
the role of hunting and meat-eating in the evolution of Homo sapiens [cf. van
Hooff, 1990; McGrew, 1992].
METHODS
Six cases of orangutan hunting behavior and meat-eating were observed during
studies of the social behavior of the habituated wild population of orangutans in the
Ketambe area of the Gunung Leuser National Park, Sumatra, Indonesia. In addition, Carel van Schaik also provided one case of hunting, observed during a longterm field study on orangutans by his team in the Suaq Balimbiang area of the
Gunung Leuser Park. Both are areas of undisturbed tropical rain forest.
The data of Ketambe come from observations by the first author and by local
field assistants and students and were collected during focal subject follows. These
cases as well as the Suaq case involved a slow loris as the prey.
RESULTS
In Ketambe, two adult females, each accompanied by an offspring, were involved; the female Getty, fully wild after having been rehabilitated, was involved
five times and female Yet, a wild animal born in Ketambe, was involved once.
The prey was always a slow loris, in one case a mother with her offspring.
All captures were made up in trees at a height of more than 10 m. Also, foodsharing was observed in two cases. This was a passive food-sharing, in which the
female Getty permitted her offspring to take food from her.
In three of the six cases (Getty twice, Yet once), the whole process was
seen, from the discovery of the slow loris through its consumption. In the
other three cases the discovery, by Getty, was not observed. The following
steps were distinguishable:
1. Discovery. In two cases Getty was foraging in epiphytes when she found a
slow loris. In another case Yet entered a fruit tree and then suddenly sat down
and stared at a slow loris right in front of her. She slapped it until the slow loris
fell to the ground. When the prey fled on the ground, the orangutan pursued it
while making high-pitched hooting sounds.
2. Capture. In three cases in which the whole process was observed, the orangutan was seen to hit the slow loris hard on the back. Immediately afterwards
the orangutan grabbed the slow loris by the scruff of its neck. In one case, Getty
stared at the slow loris for about 15 min before approaching it slowly and carefully. Then she grabbed the slow loris by the scruff of the neck.
3. Consumption. The orangutan instantly killed the slow loris by biting
Meat-Eating by Sumatran Orangutans / 161
through its skull. The orangutan then sat down or made a small nest at a height
of 10–15 m and started to eat the prey. First, she sucked out the brain and eyes
and ate the palms of the hands. She ripped the neck and the chest apart with
her teeth and ate the genitals. She picked out the entrails from the body cavity
using a finger like a fish hook. She continued tearing apart the body using her
teeth. She chewed all the bones and skin thoroughly before swallowing. After 2 h
all body parts had been eaten. One female, at Suaq, dropped a small piece of
bone and a small wadge of skin and bone.
In all six cases the female was accompanied by an offspring, but there were
no others around them. Passive food-sharing occurred in two cases between Getty
and her 5-year-old son, Herman. He repeatedly approached his mother with infantile vocalizations, but she always slapped him or turned her back on him.
After several such attempts Herman twice succeeded in getting some body part
of the slow loris and moved about two arm lengths away from his mother to feed
on his prize. She looked at her son but otherwise did not react.
In the other four cases, the offspring merely approached the mother and
showed interest in what she ate but never came very close to her.
Over the past few years systematic habituation of the orangutan population
at Suaq Balimbiang has taken place, and observations (approximately 2,000 h)
of their behavior and ecology have been made. One case of prey capture has been
seen; a natal female, Abby, got hold of a slow loris and ate it.
DISCUSSION
Predation by orangutans on vertebrates is a rare occurrence, considering the
many hours of observation in the wild. It is of the stumble-upon-and-capture
type, and in this respect it differs from the hunting that has been described for
chimpanzees. Boesch and Boesch [1989] and Boesch [1994a,b] have suggested
that hunting in Taï Forest chimpanzees can be deliberate and strategic, and,
more importantly, that it need not be triggered by accidental encounter with a
prey; the apes seem to be actively searching for prey.
Eight cases of predation by orangutans on vertebrates have been recorded:
the seven reported here, plus the one by Sugardjito and Nurhuda [1981]. Four
individuals were involved, all females. In contrast, chimpanzee hunting is mostly
[Boesch, 1994,a,b; Stanford et al., 1994a,b] although not exclusively done by males
[Takahata et al., 1984; Uehara et al., 1992] whereas foraging for invertebrate
prey is done more by females [McGrew, 1979; Uehara, 1984]. In olive baboons
(Papio anubis), males also do by far the most captures of vertebrates [Harding,
1973]. Still, our data are too few to conclude that orangutan females more often
secure vertebrate prey.
Observations by Rodman [1977], Sugardjito [1986], and the first author [unpublished] suggest that females spend more time on foraging for insects than do
males. If there is indeed a systematic sex difference, this would imply a difference in the selective direction of attention in searching for food, which might
relate to a sex difference in capturing vertebrate prey.
Here one orangutan made five captures and two others made one each. The
data are too scant to draw firm conclusions about the distribution of meat-eating
in the population. Capture of a slow loris may, therefore, be idiosyncratic and
opportunistically developed, because the skewed distribution of the captures is
not due to a skewed distribution of focal observations. Figure 1 demonstrates
that Getty has not been followed more often than the other orangutans.
162 / Utami and van Hooff
Fig. 1. The recorded slow loris captures and the total number of hours of focal observation for
the most frequently observed orangutans at Ketambe from 1989 till 1994.
Getty is a rehabilitant, one of the few successful ones at Ketambe. She came
to the Ketambe station in 1979 when she was about 6 years old, in comparatively good shape. She was wild and avoided people, suggesting that she had not
been with humans for long. She was released into the forest after only 3 weeks,
rarely came to the feeding site, and disappeared temporarily after 3 months
[Schürmann, personal communication]. It is unlikely that she had become accustomed to meat-eating during her stay with humans, because orangutans kept by
Indonesian citizens tend to be fed with rice and fruits. But even if she had eaten
meat occasionally, it is unlikely that this explains the development of the preycapturing in orangutans generally. The occurrence of the behavior in two other
individuals, one of whom lives more than 100 km away from the others, refutes
the explanation that it is an artifact of habituation.
A disproportionate number of captures by Getty could be explained by uneven distribution of slow lorises over the home ranges of the orangutans. There
might be slow lorises in the home range of some orangutans and not in that of
others. The distribution of the captures suggests a certain clustering, even within
Getty’s home range. However, this part of her home range overlaps the home
ranges of seven other females and about ten males (Fig. 2). Therefore, these
other animals have had an opportunity to develop the behavior. This also suggests that orangutan predation on slow lorises may be an idiosyncratic trait rather
than a general behavior.
CONCLUSIONS
1. In orangutans, solitary, opportunistic, reactive hunting was seen to get a
slow moving prey, the slow loris.
2. Only four females from two large, habituated populations were involved in
this behavior. One female made five captures, suggesting that the behavior may
be idiosyncratic.
3. Unlike the other hunting ape, the chimpanzee, whose hunting is more
often done by males, all eight cases by orangutans were by females.
4. Female orangutans may be more prone to develop the habit as they
spend more time searching for invertebrates and thus may be more likely to
stumble upon slow lorises, nocturnal animals which hide in the foliage during
the day.
Meat-Eating by Sumatran Orangutans / 163
Fig. 2. Home range boundaries of eight adult females living in the Ketambe research area. Capture sites
also are shown.
ACKNOWLEDGMENTS
This paper is based on observations from a 6 year field study in Sumatra,
financed by the Netherlands Foundation for the Advancement of Tropical Research. We are indebted to Prof. Carel van Schaik for allowing us to report on a
case of hunting in Suaq Balimbiang. We are grateful to Romy Steenbeek, Liesbeth
Sterck, Tatang Mitra Setia, and the students at the Ketambe Research Centre
for comments, discussions, and support. We also thank Dr. Erna Suzana, Matplin,
Usman, and Rizal for their help in collecting the data. We thank Eleni Nikitopoulos
and William McGrew for correcting the English text. We are grateful to the Dean
of the Faculty of Biology, UNAS, Jakarta (Dr. Kasim Moosa) and the Indonesian
Nature Conservation Service (PHPA) for permitting this research. We owe very
special thanks to the late Mrs. Nina Sulaiman.
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