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Serge A. Wich - One of the best experts on this subject based on the ideXlab platform.

  • land cover changes predict steep declines for the sumatran orangutan Pongo Abelii
    Science Advances, 2016
    Co-Authors: Ian Singleton, Serge A. Wich, Sri Suci Utami Atmoko, Matthew G Nowak, Gonda Nisam, Sugesti Mhd Arif, Rudi H Putra, Rio Ardi, Gabriella Fredriksson
    Abstract:

    Positive news about Sumatran orangutans is rare. The species is critically endangered because of forest loss and poaching, and therefore, determining the impact of future land-use change on this species is important. To date, the total Sumatran orangutan population has been estimated at 6600 individuals. On the basis of new transect surveys, we estimate a population of 14,613 in 2015. This higher estimate is due to three factors. First, orangutans were found at higher elevations, elevations previously considered outside of their range and, consequently, not surveyed previously. Second, orangutans were found more widely distributed in logged forests. Third, orangutans were found in areas west of the Toba Lake that were not previously surveyed. This increase in numbers is therefore due to a more wide-ranging survey effort and is not indicative of an increase in the orangutan population in Sumatra. There are evidently more Sumatran orangutans remaining in the wild than we thought, but the species remains under serious threat. Current scenarios for future forest loss predict that as many as 4500 individuals could vanish by 2030. Despite the positive finding that the population is double the size previously estimated, our results indicate that future deforestation will continue to be the cause of rapid declines in orangutan numbers. Hence, we urge that all developmental planning involving forest loss be accompanied by appropriate environmental impact assessments conforming with the current national and provincial legislations, and, through these, implement specific measures to reduce or, better, avoid negative impacts on forests where orangutans occur.

  • preliminary data on the highland sumatran orangutans Pongo Abelii of batang toru
    2014
    Co-Authors: Serge A. Wich, Matthew G Nowak, Graham Usher, H H Peters, Mokhamad Faesal Rakhman Khakim, Gabriella Fredriksson
    Abstract:

    Orangutans are the only great apes occurring in Asia (Caldecott and Miles 2005) and knowledge of their behavioral ecology comes from a number of long-term studies on Sumatra and Borneo (Wich et al. 2009).

  • marked population structure and recent migration in the critically endangered sumatran orangutan Pongo Abelii
    Journal of Heredity, 2013
    Co-Authors: Alexander Nater, Ian Singleton, Serge A. Wich, Gabriella Fredriksson, Natasha Arora, Maja P Greminger, Carel P Van Schaik, Dyah Perwitasarifarajallah, Joko Pamungkas, Michael Krutzen
    Abstract:

    A multitude of factors influence how natural populations are genetically structured, including dispersal barriers, inhomogene ous habitats, and social organization. Such population subdivision is of special concern in endangered species, as it may lead to reduced adaptive potential and inbreeding in local subpopulations, thus increasing the risk of future extinctions. With only 6600 animals left in the wild, Sumatran orangutans (Pongo Abelii) are among the most endangered, but also most enigmatic, great ape species. In order to infer the fine-scale population structure and connectivity of Sumatran orangutans, we analyzed the most comprehensive set of samples to date, including mitochondrial hyper-variable region I haplotypes for 123 individuals and genotypes of 27 autosomal microsatellite markers for 109 individuals. For both mitochondrial and autosomal markers, we found a pronounced population structure, caused by major rivers, mountain ridges, and the Toba caldera. We found that genetic diversity and corresponding long-term effective population size estimates vary strongly among sampling regions for mitochondrial DNA, but show remarkable similarity for autosomal markers, hinting at male-driven long-distance gene flow. In support of this, we identified several individuals that were most likely sired by males originating from other genetic clusters. Our results highlight the effect of natural barriers in shaping the genetic structure of great ape populations, but also point toward important dispersal corridors on northern Sumatra that allow for genetic exchange.

  • Behavioral, Ecological, and Evolutionary Aspects of Meat-Eating by Sumatran Orangutans (Pongo Abelii)
    International Journal of Primatology, 2012
    Co-Authors: Madeleine E Hardus, Sri Suci Utami Atmoko, Adriano R Lameira, Han De Vries, Astri Zulfa, Serge A. Wich
    Abstract:

    Meat-eating is an important aspect of human evolution, but how meat became a substantial component of the human diet is still poorly understood. Meat-eating in our closest relatives, the great apes, may provide insight into the emergence of this trait, but most existing data are for chimpanzees. We report 3 rare cases of meat-eating of slow lorises, Nycticebus coucang , by 1 Sumatran orangutan mother–infant dyad in Ketambe, Indonesia, to examine how orangutans find slow lorises and share meat. We combine these 3 cases with 2 previous ones to test the hypothesis that slow loris captures by orangutans are seasonal and dependent on fruit availability. We also provide the first (to our knowledge) quantitative data and high-definition video recordings of meat chewing rates by great apes, which we use to estimate the minimum time necessary for a female Australopithecus africanus to reach its daily energy requirements when feeding partially on raw meat. Captures seemed to be opportunistic but orangutans may have used olfactory cues to detect the prey. The mother often rejected meat sharing requests and only the infant initiated meat sharing. Slow loris captures occurred only during low ripe fruit availability, suggesting that meat may represent a filler fallback food for orangutans. Orangutans ate meat more than twice as slowly as chimpanzees ( Pan troglodytes ), suggesting that group living may function as a meat intake accelerator in hominoids. Using orangutan data as a model, time spent chewing per day would not require an excessive amount of time for our social ancestors (australopithecines and hominids), as long as meat represented no more than a quarter of their diet.

  • which factors determine orangutan nests detection probability along transects
    Tropical Conservation Science, 2011
    Co-Authors: Serge A. Wich, Ryan H Boyko
    Abstract:

    Effective conservation needs a solid baseline of animal distribution, density, and abundance data to base management strategies on and evaluate the effectiveness of conservation efforts on the species of interest. For many species it is not feasible to directly count individuals, and scientists are forced to use indirect methods that can provide estimates of density and abundance. For orangutans nest counts are the most often used indirect sign of presence. Models used for density and abundance estimates are based on a set of assumptions about the observations. Here we analyze the effect of several factors (distance to transect, height, decay stage, and observer experience) on the probability that an orangutan (Pongo Abelii) nest is found along a line transect. The results indicate that all factors significantly influence nest detection. Orangutan density estimates varied between the teams with the lowest estimate being approximately 83% of the highest estimate and orangutan density showed a positive correlation to experience level. We use these results to propose a new approach to determine orangutan density that should reduce variation between density estimates from nest surveys and therefore should lead to more reliable between-survey comparisons for orangutans and potentially other great-ape species.

C P Van Schaik - One of the best experts on this subject based on the ideXlab platform.

  • general cognitive abilities in orangutans Pongo Abelii and Pongo pygmaeus
    Intelligence, 2019
    Co-Authors: Laura Damerius, Yenny Saraswati, Maria A Van Noordwijk, Judith M Burkart, Daniel B M Haun, Zaida K Kosonen, Birute M F Galdikas, Denny Kurniawan, C P Van Schaik
    Abstract:

    Abstract For over a century, theories of human intelligence have concentrated on a single general factor, the psychometric g, which is used to estimate reasoning ability and cognitive flexibility, i.e. general intelligence. To better understand the evolution of general intelligence, it is important to identify the presence of a psychometric g in nonhuman animals, especially in primates, and to further disentangle the influences affecting its development. We therefore investigated the cognitive abilities of 53 Bornean and Sumatran orangutans to assess the presence of a psychometric g, and to explore possible influences on its expression. We did so using a set of carefully selected physical cognition tasks addressing abilities of inhibitory control, behavioral flexibility, causal reasoning, tool use, and associative- and reversal learning, and presented tasks to the subjects in the absence of human experimenters. A principal component analysis of the individuals' performances revealed a single component, which accounted for 31% of the individual variation in task performance. This g could not be explained by non-cognitive confounding variables, such as health status, island of origin, or rearing background. Furthermore, we found a modest correlation between an individual's independently assessed curiosity and g, which is consistent with the notion that accumulating experience affects the developmental construction of g. Together, our results suggest there is evidence for general intelligence in orangutans comparable to humans and chimpanzees, and thus evolutionary continuity in this trait.

  • development of foraging skills in two orangutan populations needing to learn or needing to grow
    Frontiers in Zoology, 2016
    Co-Authors: Caroline Schuppli, Maria A Van Noordwijk, Sofia I F Forss, Ellen J M Meulman, Nicole Zweifel, Kevin Lee, Evasari Rukmana, Erin R Vogel, C P Van Schaik
    Abstract:

    Background Orangutans have one of the slowest-paced life histories of all mammals. Whereas life-history theory suggests that the time to reach adulthood is constrained by the time needed to reach adult body size, the needing-to-learn hypothesis instead suggests that it is limited by the time needed to acquire adult-level skills. To test between these two hypotheses, we compared the development of foraging skills and growth trajectories of immature wild orangutans in two populations: at Tuanan (Pongo pygmaeus wurmbii), Borneo, and Suaq Balimbing (Pongo Abelii), Sumatra. We collected behavioral data on diet repertoire, feeding rates and ranging competence during focal follows, and estimated growth through non-invasive laser photogrammetry.

  • wild orangutan males plan and communicate their travel direction one day in advance
    PLOS ONE, 2013
    Co-Authors: C P Van Schaik, Laura Damerius, Karin Isler
    Abstract:

    The ability to plan for the future beyond immediate needs would be adaptive to many animal species, but is widely thought to be uniquely human. Although studies in captivity have shown that great apes are capable of planning for future needs, it is unknown whether and how they use this ability in the wild. Flanged male Sumatran orangutans (Pongo Abelii) emit long calls, which females use to maintain earshot associations with them. We tested whether long calls serve to communicate a male's ever-changing predominant travel direction to facilitate maintaining these associations. We found that the direction in which a flanged male emits his long calls predicts his subsequent travel direction for many hours, and that a new call indicates a change in his main travel direction. Long calls given at or near the night nest indicate travel direction better than random until late afternoon on the next day. These results show that male orangutans make their travel plans well in advance and announce them to conspecifics. We suggest that such a planning ability is likely to be adaptive for great apes, as well as in other taxa.

  • the natural history of sumatran orangutan Pongo Abelii
    2010
    Co-Authors: Sri Suci Utami Atmoko, C P Van Schaik
    Abstract:

    The orangutan is the only great ape of Asia. Its present range is confined to dwindling areas on the islands of Sumatra and Borneo (Rijksen and Meijaard 1999). In contrast to its African relatives, the chimpanzee, bonobo (genus Pan), and gorilla (genus Gorilla), it is extremely arboreal (the Sumatra species more so than the Borneo as Sumatra still harbors tigers). In fact, it is the largest and heaviest of all predominantly arboreal mammals. Among the diurnal primates, it is, moreover, exceptional in that it is comparatively solitary.

  • the status of the sumatran orang utan Pongo Abelii an update
    Oryx, 2003
    Co-Authors: Serge A. Wich, Sri Suci Utamiatmoko, M L Geurts, H. D. Rijksen, I Singleton, C P Van Schaik
    Abstract:

    Abstract The Sumatran orang-utan Pongo Abelii is have recently caused local extinctions. We combinecategorized as Critically Endangered on the 2002 IUCN these results with other available information to provideRed List. Although several reports have suggested that a summary of the current distribution of P. Abelii inthe species occurs in the region to the south of Lake Sumatra and, based on our surveys, previous populationToba in Sumatra, Indonesia, their distribution is poorly estimates, and estimates of losses, we speculate that onlyknown. In order to determine whether orang-utans still c . 3,500 orang-utans still occur in the wild in Sumatra atoccur in this region we surveyed areas in which orang- the end of 2002.utans have been reported as well as a number of otherforested areas. Orang-utan signs were found in only Keywords Indonesia, Lake Toba, orang-utan, Pongotwo areas. This indicates that habitat loss and hunting Abelii , Primates, Sumatra.categorized on the 2002 IUCN Red List as EndangeredIntroductionand the Sumatran orang-utan as Critically EndangeredOrang-utans (

Wishnu Nurcahyo - One of the best experts on this subject based on the ideXlab platform.

  • Redescription and resurrection of Bertiella satyri (Cestoda, Anoplocephalidae) parasitizing the orangutan (Pongo Abelii) in Indonesia
    Parasitology Research, 2011
    Co-Authors: Ivona Foitova, Martina Vyskocilova, Sarka Masova, Božena Koubková, František Tenora, Vlastimil Baruš, Iveta Hodová, Wishnu Nurcahyo
    Abstract:

    The tapeworm species Bertiella satyri from a semi-wild Sumatran orangutan (Pongo Abelii: Ponginae) is redescribed and the sequence of its 18S rDNA is presented. The tapeworms parasitizing the genera Pan, Pongo, Homo and Hylobates from Museum National d'Histoire Naturelle, Paris and from Museum d´Histoire Naturelle, Geneve are also presented. The validity of B. satyri is confirmed. B. satyri (BSA) differs from the most similar species Bertiella studeri (BSTU) in the following characteristics: (1) testes number, BSTU 300–400; BSA 116–124, (2) genital opening, BSTU regularly alternate; BSA irregularly alternate, (3) Cirrus-sac, BSTU short, 0.250–0.320, does not reach excretory ducts; BSA long, 0.630 × 0.495, reaches excretory ducts, (4) egg size, BSTU 0.053–0.060; BSA 0.030–0.051, (5) host BSTU Pan troglodytes, Africa; BSA Pongo pygmaeus, P. Abelii, Indonesia (Borneo, Sumatra). Both species differ according to our material and the name B. satyri (Blanchard, 1891) is resurrected.

  • Description of Lemuricola ( Lemuricola ) Pongoi —male (Nematoda: Enterobiinae) parasitising orangutan Pongo Abelii
    Parasitology Research, 2010
    Co-Authors: Ivona Foitova, Sarka Masova, Božena Koubková, Vlastimil Baruš, Wishnu Nurcahyo
    Abstract:

    The study presents the first description of male specimen (allotype) of the pinworm species Lemuricola (Lemuricola) Pongoi, parasitising Sumatran orangutan (Pongo Abelii) from Sumatra (Indonesia). The male specimen morphology presents all features fully corresponding with diagnose of the genus and subgenus Lemuricola. We are agreeing that Protenterobius is synonymous with Lemuricola because the length of tail appendix in males is not a sufficient feature for separation of the genera or subgenera. For L. (L.) Pongoi male are characteristic features: body length (4,803 µm), total oesophagus length (530), tail length (235), tip of tail length (188) and spicule length (90).

  • Two remarkable pinworms (Nematoda: Enterobiinae) parasitizing orangutan (Pongo Abelii) in the Sumatra (Indonesia) including Lemuricola (Protenterobius) Pongoi n.sp.
    Helminthologia, 2009
    Co-Authors: Ivona Foitova, Božena Koubková, Iveta Hodová, V. Baruš, Wishnu Nurcahyo
    Abstract:

    Two species of pinworms (Enterobiinae) were collected from fresh faeces of semi-wild orangutans Pongo Abelii Lesson living in northern Sumatra (Indonesia). The female of Enterobius (Enterobius) buckleyi Sandosham, 1950 is redescribed. Lemuricola ( Protenterobius) Pongoi n. sp. is described on the basis of females (no males are available) and distinguished from L. (P.) nycticebi (Baylis, 1928) by cephalic and mouth morphology (head and teeth superstructures), body (9.85–15.46 mm) and tail (2.34–2.95 mm) length, smaller eggs (48–56 x 22–28 μm), longer vulva distance from anterior extremity (2.05–3.09 mm) and other features. Characteristic is the total body length/oesophagus length ratio (1: 15.3–22.0). Both nematode species were studied using scanning electron microscopy for the first time.

  • two remarkable pinworms nematoda enterobiinae parasitizing orangutan Pongo Abelii in sumatra indonesia
    2008
    Co-Authors: Ivona Foitova, Božena Koubková, Vlastimil Baruš, Iveta Hodová, Wishnu Nurcahyo
    Abstract:

    Dva významne druhy roupů (Nematoda: Enterobiinae) parazitujici u orangutanů (Pongo Abelii) na Sumatře (Indonesie)

  • A new nematode, Pongobius hugoti gen. et sp. n. from the orangutan Pongo Abelii (Primates: Hominidae)
    Helminthologia, 2007
    Co-Authors: V. Baruš, Ivona Foitova, Božena Koubková, Iveta Hodová, A. Šimková, Wishnu Nurcahyo
    Abstract:

    Light and scanning electron microscopical examination and molecular analysis of pinworm samples collected from the Sumatran orangutan ( Pongo Abelii ) from Sumatra (Indonesia) revealed the presence of a new taxon, Pongobius hugoti gen. et sp. n. (Oxyuridae: Enterobiinae). The monotypic genus Pongobius is characterised by the presence of a triangular mouth, three rounded teeth and three chisel-like inner teeth in the buccal cavity, an oesophagus with a long pharyngeal part, corpus posteriorly slightly enlarged and continuing as a pyriform bulb, isthmus absent. These features differentiate P. hugoti from all members of the subfamily Enterobiinae. The male has a long caudal appendix (> 50% of total tail length). Molecular analysis of the new taxon is presented for more precise identification.

Ivona Foitova - One of the best experts on this subject based on the ideXlab platform.

  • molecular identification systematics evolutionary history ofstrongyloides spp in orangutans a comparative study betweenwild and semi wild Pongo Abelii Pongo pygmaeus
    2014
    Co-Authors: Erhan Yalcindag, Peter Stuart, Hiroo Hasegawa, Wisnu Nucarhyo, Helen C Morroghbernard, Cathleen Nguyen, Radka Peckova, Maria A Van Noordwijk, Ivona Foitova
    Abstract:

    Presenter’s Email: e.yalcindag@gmail.com Several pathogenic parasites threaten great apes survival. Parasites are primarily transmited between captive, semi captive and wild ape populations, between apes and other wildlife species and/or humans and their livestock. Several viral diseases and parasitic infections have been well-studied in African apes. However, the distribution and transmission of parasites in orangutans, (the only non-African great apes), are still comparatively poorly understood. Recently, the total number and distribution of orangutans has reduced drastically, primarily due to habitat lost. Several studies have been done on captive and semi-captive species. Information from wild populations is still missing. The aim of this study is to identify Strongyloides species infecting wild and semi-wild orangutans by carrying out PCR assays on 410 fecal samples collected by the Orangutan Health Project. These samples have been collected from 110 wild individual orangutans from 2004 to 2011 in 4 different sites in Indonesia from both Sumatra and Borneo. We will investigate; which Strongyloides species naturally infect orangutans and compare parasitic infection observed in the two Orangutans species, Pongo Abelii and Pongo pygmaeus. Factors including age, sex, time of year and population structure will be investigated to identify any risk factors associated with infection. Results will be discussed. The study was financially supported by the UMI - Saving of Pongidae Foundation and partly by GA P505/11/1163.

  • Redescription and resurrection of Bertiella satyri (Cestoda, Anoplocephalidae) parasitizing the orangutan (Pongo Abelii) in Indonesia
    Parasitology Research, 2011
    Co-Authors: Ivona Foitova, Martina Vyskocilova, Sarka Masova, Božena Koubková, František Tenora, Vlastimil Baruš, Iveta Hodová, Wishnu Nurcahyo
    Abstract:

    The tapeworm species Bertiella satyri from a semi-wild Sumatran orangutan (Pongo Abelii: Ponginae) is redescribed and the sequence of its 18S rDNA is presented. The tapeworms parasitizing the genera Pan, Pongo, Homo and Hylobates from Museum National d'Histoire Naturelle, Paris and from Museum d´Histoire Naturelle, Geneve are also presented. The validity of B. satyri is confirmed. B. satyri (BSA) differs from the most similar species Bertiella studeri (BSTU) in the following characteristics: (1) testes number, BSTU 300–400; BSA 116–124, (2) genital opening, BSTU regularly alternate; BSA irregularly alternate, (3) Cirrus-sac, BSTU short, 0.250–0.320, does not reach excretory ducts; BSA long, 0.630 × 0.495, reaches excretory ducts, (4) egg size, BSTU 0.053–0.060; BSA 0.030–0.051, (5) host BSTU Pan troglodytes, Africa; BSA Pongo pygmaeus, P. Abelii, Indonesia (Borneo, Sumatra). Both species differ according to our material and the name B. satyri (Blanchard, 1891) is resurrected.

  • Description of Lemuricola ( Lemuricola ) Pongoi —male (Nematoda: Enterobiinae) parasitising orangutan Pongo Abelii
    Parasitology Research, 2010
    Co-Authors: Ivona Foitova, Sarka Masova, Božena Koubková, Vlastimil Baruš, Wishnu Nurcahyo
    Abstract:

    The study presents the first description of male specimen (allotype) of the pinworm species Lemuricola (Lemuricola) Pongoi, parasitising Sumatran orangutan (Pongo Abelii) from Sumatra (Indonesia). The male specimen morphology presents all features fully corresponding with diagnose of the genus and subgenus Lemuricola. We are agreeing that Protenterobius is synonymous with Lemuricola because the length of tail appendix in males is not a sufficient feature for separation of the genera or subgenera. For L. (L.) Pongoi male are characteristic features: body length (4,803 µm), total oesophagus length (530), tail length (235), tip of tail length (188) and spicule length (90).

  • two cases of mother infant cannibalism in orangutans
    Primates, 2009
    Co-Authors: David Dellatore, C. Waitt, Ivona Foitova
    Abstract:

    Observations of ape cannibalism have to this point been limited to chimpanzees (Pan troglodytes) where it is associated with infanticide and consumption by unre- lated individuals (Watts and Mitani, Primates 41(4):357- 365, 2000). Here we report for the first time observations of two unrelated female Sumatran orangutans (Pongo Abelii) cannibalizing the remains of their infants on different occasion, a behavior never before reported in any ape species. The two orangutans were wild-born rehabilitated individuals, and had been reintroduced to an area hosting a largely unregulated primate tourism industry and experi- enced restricted ranging conditions. Though it is possible that this is a strategy to regain energy and nutrients or a result of individual history, comparative data suggest that this is an aberrant behavior which may be linked to envi- ronmental stressors within the area.

  • Two remarkable pinworms (Nematoda: Enterobiinae) parasitizing orangutan (Pongo Abelii) in the Sumatra (Indonesia) including Lemuricola (Protenterobius) Pongoi n.sp.
    Helminthologia, 2009
    Co-Authors: Ivona Foitova, Božena Koubková, Iveta Hodová, V. Baruš, Wishnu Nurcahyo
    Abstract:

    Two species of pinworms (Enterobiinae) were collected from fresh faeces of semi-wild orangutans Pongo Abelii Lesson living in northern Sumatra (Indonesia). The female of Enterobius (Enterobius) buckleyi Sandosham, 1950 is redescribed. Lemuricola ( Protenterobius) Pongoi n. sp. is described on the basis of females (no males are available) and distinguished from L. (P.) nycticebi (Baylis, 1928) by cephalic and mouth morphology (head and teeth superstructures), body (9.85–15.46 mm) and tail (2.34–2.95 mm) length, smaller eggs (48–56 x 22–28 μm), longer vulva distance from anterior extremity (2.05–3.09 mm) and other features. Characteristic is the total body length/oesophagus length ratio (1: 15.3–22.0). Both nematode species were studied using scanning electron microscopy for the first time.

M L Geurts - One of the best experts on this subject based on the ideXlab platform.

  • dietary and energetic responses of Pongo Abelii to fruit availability fluctuations
    International Journal of Primatology, 2006
    Co-Authors: Serge A. Wich, Sri Suci Utamiatmoko, Mitra T Setia, S Djoyosudharmo, M L Geurts
    Abstract:

    Like many primates, orangutans face fluctuations in fruit availability. We show that in Ketambe (Sumatra), fruit availability fluctuations have very little influence on orangutan diet. Most importantly, the percentages of fruits including figs, fruits excluding figs, and figs in their diet do not differ significantly between periods of varying fruit availability. In addition, there is no trace of ketones in orangutan urine samples during periods of varying fruit availability. Unlike 1 orangutan population in Borneo, orangutans in Sumatra experience no prolonged negative energy budget because of fluctuations in fruit availability. Dietary data from other Sumatran and Bornean orangutan populations indicate that the pattern might be representative for a more general difference between Sumatra and Borneo, and we discuss how this might have affected orangutan reproduction and life history for the 2 species.

  • the status of the sumatran orang utan Pongo Abelii an update
    Oryx, 2003
    Co-Authors: Serge A. Wich, Sri Suci Utamiatmoko, M L Geurts, H. D. Rijksen, I Singleton, C P Van Schaik
    Abstract:

    Abstract The Sumatran orang-utan Pongo Abelii is have recently caused local extinctions. We combinecategorized as Critically Endangered on the 2002 IUCN these results with other available information to provideRed List. Although several reports have suggested that a summary of the current distribution of P. Abelii inthe species occurs in the region to the south of Lake Sumatra and, based on our surveys, previous populationToba in Sumatra, Indonesia, their distribution is poorly estimates, and estimates of losses, we speculate that onlyknown. In order to determine whether orang-utans still c . 3,500 orang-utans still occur in the wild in Sumatra atoccur in this region we surveyed areas in which orang- the end of 2002.utans have been reported as well as a number of otherforested areas. Orang-utan signs were found in only Keywords Indonesia, Lake Toba, orang-utan, Pongotwo areas. This indicates that habitat loss and hunting Abelii , Primates, Sumatra.categorized on the 2002 IUCN Red List as EndangeredIntroductionand the Sumatran orang-utan as Critically EndangeredOrang-utans (