Newestimates of orangutan density in Sungai Palin watershed, Kapuas Hulu,West Kalimantan, Indonesia ACHMAD YANUAR,JAN F EHS E,DAV I D CHIVERS and J ITO S UGARDJIT O


Abstract Pongo pygmaeus pygmaeus is a subspecies of Bornean orangutan whose distribution is restricted to the northern part of the Kapuas River, West Kalimantan, and is categorized as Critically Endangered. In October 2017 we carried out a survey to estimate orangutan density in the peat-swamp forests of the Sungai Palin watershed, of the upper Kapuas river, Kapuas Hulu,West Kalimantan, Indonesia. Surveys for orangutans in 1991, in nearby Nanga Awen, had indicated the presence of orangutans in the peat-swamp forests of this area. We used distance sam- pling techniques to estimate orangutan densities from nest observations. We recorded 76 orangutan nests along 4.5 km transects in Sungai Palin in 2017, and 71 orangutan nests were observed along 4.3 km transects in Nanga Awen in 1991, giving densities of 1.29 and 2.62 individuals/km2, respectively. The results of this orangutan survey can be used as a baseline for monitoring of orangutan popula- tions for conservation and management of this watershed landscape.


Keywords Indonesia, limited production forest, Nanga Awen, orangutan, Pongo pygmaeus pygmaeus, small popu- lation, Sungai Palin, transect survey


et al., 2017) in northern Sumatra and Pongo pygmaeus in Borneo. The latter has three subspecies: the north-western Bornean orangutan Pongo pygmaeus pygmaeus, the central Bornean orangutan Pongo pygmaeus wurmbii and the north-eastern Bornean orangutan Pongo pygmaeus morio (Groves, 1999, 2001), all of which are categorized as Critically Endangered on the IUCN Red List (Ancrenaz et al., 2016). Pongo pygmaeus pygmaeus is restricted to the upper Kapuas River in West Kalimantan (Indonesia) and Sarawak (Malaysia). It has the smallest population of the three subspecies, with a total of 3,000–4,500 individuals (Wich et al., 2008) of which there are c. 1,300 in Sarawak


T ACHMAD YANUAR (Corresponding author, orcid.org/0000-0001-8015-7793)


and JITO SUGARDJITO Department of Biology, Universitas Nasional, Jl. RM. Harsono, Jakarta 12550, Indonesia. E-mail ay232ster@gmail.com


JAN FEHSE Value for Nature Ltd., Oxford, UK, and LTS International Ltd., Edinburgh, UK


DAVID CHIVERS Selwyn College, University of Cambridge, Cambridge, UK


hree Asian great ape species occur in Sumatra and Borneo: Pongo abelii and Pongo tapanuliensis (Nater


(Ancrenaz et al., 2005; Ancrenaz, 2006; WWF Malaysia, 2018). Bornean orangutans are known to live in primary and secondary forests and are typically found in peat- swamp forest and lowland dipterocarp forest at ,500 m altitude (Rijksen & Meijaard, 1999). Only an estimated 25% of orangutan populations live within protected areas (Singleton et al., 2004; IUCN, 2012). Most orangutan range remains poorly documented, and


updating and expanding baseline data, especially in unpro- tected areas such as limited production forests (forests in which there is selective logging) and production forests, is essential (Wich et al., 2012). The rate of deforestation in Kalimantan is increasing, threatening orangutan habitats. Improvedmanagement is thus needed for conserving orang- utan populations outside protected areas by involving all stakeholders, developing and implementing best manage- ment practices, and working with local communities to avoid or mitigate negative human–wildlife interactions. Two protected areas, Danau Sentarum Wildlife Reserve


and Betung Kerihun National Park, in the upper Kapuas watershed, were home to relatively large populations of the Bornean orangutan until the 1990s (Meijaard et al., 1996). However, during 1973–1997 almost 30%of habitat dis- appeared in and around Danau Sentarum Wildlife Reserve (Russon et al., 2000) and it is likely that the orangutan popu- lation in this area has declined. Orangutans are, however, still commonly encountered in the unprotected areas of Sungai Palin and Nanga Awen, which lie between Danau Sentarum Wildlife Reserve and Betung Kerihun National Park (Fig. 1), although anecdotal evidence suggests that the number of orangutans in these two areas has fallen as a result of forest degradation. In October 2017 we conducted orangutan population


surveys in peat-swamp forests that are limited production forests under the authority of the local forest department of Kapuas Hulu and the local community of Nanga Lauk village. We established five line transects (0.6–1.2 km long, with a total length of c. 4.5 km) from the bank of the Palin River in Sungai Palin towards peat-swamp forests (Fig. 1). We counted orangutan nests along these transects in 5 days of survey walks, each with two observers. A previous survey, using the the same method, under-


Received 10 January 2019. Revision requested 12 February 2019. Accepted 15 July 2019. First published online 25 November 2019. Oryx, 2020, 54(6), 763–766 © 2019 Fauna & Flora International doi:10.1017/S0030605319000875


taken in 1991 in Nanga Awen, c. 20 km away from Sungai Palin in the same landscape, recorded orangutan nests along three transects (1.0–1.2 km long,withatotallengthof 4.3 km). Here we also analyse these previously unpublished data, to determine orangutan density in August 1991 as a reference point for comparison with our 2017 survey.


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