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Asian Primates Journal 2(1), 2011
10
FIRST SIGHTING OF BORNEAN ORANGUTAN
TWINS IN THE WILD
Benoit Goossens
1,2
* Mohd Daisah Kapar
3
, Suhailie Kahar
4
, and Marc Ancrenaz
3
1
Danau Girang Field Centre, c/o Sabah Wildlife Department, Wisma MUIS, 88100 Kota Kinabalu, Sabah, Malaysia. E-mail:
goossensbr@cardiff.ac.uk
2
Cardiff University, Cardiff School of Biosciences, Biomedical Sciences Building, Museum Avenue, Cardiff CF10 3AX, UK.
E-mail: goossensbr@cardiff.ac.uk
3
Kinabatangan Orangutan Conservation Project, PO Box 3109, 90734 Sandakan, Sabah, Malaysia. E-mail: marc.ancrenaz@
yahoo.com
4
Red Ape Encounters, PO Box 3109, 90734 Sandakan, Sabah, Malaysia.
* Corresponding author
ABSTRACT
Twinning is a rare event in great apes, and has never been reported in wild orangutans to date. In this paper, we report the rst
sighting of Bornean Orangutan (Pongo pygmaeus) twins in the wild. In October 2007, we observed a female Northeast Bornean
Orangutan (P. pygmaeus morio) carrying two young twins aged four to six months old along the Kinabatangan River, Sabah,
Malaysia. The same family unit (adult female and twins) was observed in November 2009, at the same location, indicating that
the two offspring survived the rst 2.5 years of their life. They appeared very healthy suggesting that the mother was able to
care for two offspring over this period.
Keywords: Pongo pygmaeus morio, Borneo, Kinabatangan, reproduction, twinning
INTRODUCTION
In captivity, twinning is a rare event with orangutan
(Pongo spp.): from a sample of 626 orangutan preg-
nancies recorded in ISIS and the Orangutan Stud-
book between 1968 and 1985, Seal et al. (1985) re-
ported 11 pairs of twins or 1.1% of the sample size
(see also Geissmann, 1989 for a review). This rate
is similar in other hominids (great apes and humans
alike). The rst-ever twin birth in captivity took place
in 1968 at Woodland Park Zoo, in Seattle, Washington
(Heinrichs & Dillingham, 1970), and the twins were
still alive 40 years later (The Seattle Times 24 Febru-
ary 2008: http://seattletimes.nwsource.com/html/lo-
calnews/2004197844_orangs24m.html). In 1985, an
orangutan gave birth to twins at the Audubon Zoo in
New Orleans. More recently, in December 2003, non-
identical orangutan twins were born at a wildlife park in
Florida – the rst recorded captive twin birth for almost
20 years. Taxonomic information is unavailable either
for these captive-born twins or their parents. Further-
more, Bornean and Sumatran orangutans in American
zoos were rather mixed at that time.
Only single infants have been observed with wild
orangutans (Markham, 1995). In this paper, we report
the rst sighting of twins of Bornean Orangutan Pongo
pygmaeus (Linnaeus), and specically of Northeast
Bornean Orangutan P. pygmaeus morio (Owen) in the
wild.
METHODS
Observations were all from a boat while cruising
along the Kinabatangan River in search of primates
close to the study site of the Kinabatangan Orangu-
tan Conservation Project (KOCP). The rst observa-
tions were recorded by BG on 23 October 2007 and
three days later by MDK on 26 October 2007. The
orangutans were observed in a g tree (Ficus race-
mosa L.) located on the edge of the river in Lot 1 of
the Lower Kinabatangan Wildlife Sanctuary (LKWS:
N5°33’01.44”, E118°17’17.45”). Pictures were taken
by Mr Jorge Camilo Valenzuela, a professional pho-
tographer, who was accompanying BG. This female
and her twins have been subsequently reported to
KOCP researchers on a regular basis by various sourc-
es (tourists, tour guides, villagers). On 15 November
2009, MDK and SK spotted at the same location the
same adult female with a pair of young infants aged
between 2.5 and 3 years old.
Asian Primates Journal 2(1), 2011
11
RESULTS AND DISCUSSION
On the rst day of sighting, BG observed a total of
four orangutans in the same g tree: one adult female
with two babies of equal size clinging to her (see Fig. 1),
accompanied by one adolescent (7 to 8 years old) only
a few metres away from the trio. We assume that this
adolescent was the older offspring of the same female
(Goossens et al., 2006). During the rst two sightings,
the twin babies were holding on tightly to both sides of
the female’s chest while the mother was feeding on gs
or moving in the tree. The babies were observed suck-
ling several times at this time. Based on photographs,
we estimated the age of the twins to be between four
and six months. Two years later, the same female was
observed again with two juveniles of identical age (less
than three years old). No other female was observed in
the area, suggesting that the female was the mother
of both of the two juveniles. The two juveniles were
observed playing with each other, and interacting with
the mother. They appeared very healthy.
This is the rst reported sighting of orangutan twins
in the wild. However, the absence of any records of
orangutan twins in the wild does not mean that it has
not happened before. It may be that orangutans in the
wild have had miscarriages when carrying twins, as
recorded three times amongst nine sets of orangutan
twins in captivity (Seal et al., 1985). It is also possible
that one of the twins often dies shortly after birth, as
perinatal mortality is reported to be higher with pri-
mate twins compared to singletons (Bond & Block,
1982). Galdikas reported on her blog (http://drbirute.
com/2009/11/22/orangutan-twins-at-camp-leakey/)
that on 15 October 2009 an orangutan female gave
birth at Camp Leakey in Tanjung Puting National Park,
Central Indonesian Borneo, but one of the infants died
shortly afterwards.
Moreover, holding two babies simultaneously may
be challenging for the mother since mutual interfer-
ence between the two newborn infants can alter their
natural ventro-ventral clinging position. As reported in
wild chimpanzees (Goodall, 1979), there is a risk of the
babies losing their grip on the mother, and being killed
as a result of falling, especially as orangutans are so
highly arboreal. Difculties in carrying twins seem only
to last for a short time in most primate species, but
can lead to the death or abandonment of one twin by
the mother as reported in wild mountain gorillas (Watts
& Huts, 1988). With a pair of twins observed in 2007,
Fig. 1. Picture of a wild female Northeast Bornean Orangutan and her twins holding on to her chest (copyright:
Jorge Camilo Valenzuela; courtesy: Benoit Goossens)
Asian Primates Journal 2(1), 2011
12
and subsequently in 2009, it appears that this female
had overcome this issue. On the other hand, the fe-
male must look for larger quantities of food to produce
the extra milk necessary to feed the pair. In one pair
of captive orangutan twins, one baby died four weeks
after birth due to insufcient milk production by the
mother, even though the female had easy access to
food (Lang, 1973). Malnutrition and subsequent death
of one twin was also observed in wild chimpanzees
(Goodall, 1979). Here, the second observation of the
mother and twins aged about three years old, appear-
ing very healthy, show that this wild orangutan female
had been able to produce enough milk to feed them
for almost three years. During the last encounter, the
twins were observed feeding directly on Ficus leaves,
indicating that the weaning process had been initiated.
Although we can conrm that the twins have survived
their childhood stage, it is still not known whether they
will survive until they become fully independent, which
happens between six and nine years of age (Markham,
1995; Delgado & van Schaik, 2000).
ACKNOWLEDGMENTS
We thank the Economic Planning Unit for permission
to conduct research in Sabah and the Sabah Wildlife
Department and Dr Laurentius Ambu for permission to
conduct research in the Lower Kinabatangan Wildlife
Sanctuary. We also extend our thanks to our nancial
partners: Darwin Initiative for the Survival of Species
(Grant no. 14/014, DEFRA, UK); zoos of Pittsburgh,
Cleveland, Columbus, Philadelphia, Phoenix, Oregon,
Saint Louis, Brevard, Houston, Woodland Park, Sea
World & Bush Gardens, Chester, Apenheul, Beau-
val and La Palmyre; Abraham, World Women Work,
Shared Earth, Margot Marsh and Arcus Foundations;
USFWS Great Ape Conservation Fund, Australian
Orang-utan Project, Orangutan Conservancy, Stichting
BOS, Utah and North England Zoological Societies,
and LEAP. We nally thank Jorge Camilo Valenzuela for
kindly allowing us to use his photograph for scientic
and educational purposes.
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