A recent report, published by the Government of Indonesia with support from the Food and Agricultural Organization and Norway’s International Climate and Forest Initiative, states that orangutan populations (Pongo spp.) have increased by more than 10% in Indonesia from 2015 to 2017, exceeding the government target of an annual 2% population increase []. This assessment is in strong contrast with recent publications that showed that the Bornean orangutan (P. pygmaeus) lost more than 100,000 individuals in the past 16 years [] and declined by at least 25% over the past 10 years []. Furthermore, recent work has also demonstrated that both Sumatran orangutans (P. abelii) and the recently described Tapanuli orangutan (P. tapanuliensis) lost more than 60% of their key habitats between 1985 and 2007, and ongoing land use changes are expected to result in an 11–27% decline in their populations by 2020 []. Most scientific data indicate that the survival of these species continues to be seriously threatened by deforestation and killing [] and thus all three are Critically Endangered under the International Union for Conservation of Nature’s Red List.

Ministry of Environment and Forestry Republic of Indonesia (2018). The State of Indonesia’s Forests 2018. (Jakarta: Ministry of Environment and Forestry, Republic of Indonesia), p. 157. www.menlhk.go.id/downlot.php?file=SoiFo.pdf .

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1 Ministry of Environment and Forestry Republic of Indonesia (2018). The State of Indonesia’s Forests 2018. (Jakarta: Ministry of Environment and Forestry, Republic of Indonesia), p. 157. www.menlhk.go.id/downlot.php?file=SoiFo.pdf. 8 KSDAE (2016). 2016 Statistik. (Jakarta: Direktoral Jenderal Konservasi Sumber Daya Alam dan Ekosistem (KSDAE)), p. 139. http://ksdae.menlhk.go.id/assets/publikasi/Draft_final_Statistik_Ditjen_KSDAE_2016_CETAK_FIX.compressed_.pdf. 8 KSDAE (2016). 2016 Statistik. (Jakarta: Direktoral Jenderal Konservasi Sumber Daya Alam dan Ekosistem (KSDAE)), p. 139. http://ksdae.menlhk.go.id/assets/publikasi/Draft_final_Statistik_Ditjen_KSDAE_2016_CETAK_FIX.compressed_.pdf. 9 Marshall A.J.

Lacy R.

Ancrenaz M.

Byers O.

Husson S.

Leighton M.

Meijaard E.

Rosen N.

Singleton I.

Stephens S.

et al. Orangutan population biology, life history, and conservation. Perspectives from population viability analysis models. 4 Nowak, M.G., Rianti, P., Wich, S.A., Meijaard, E., and Fredriksson, G. (2017). Pongo tapanuliensis. The IUCN Red List of Threatened Species 2017, e.T120588639A120588662. https://doi.org/10.2305/IUCN.UK.2017-3.RLTS.T120588639A120588662.en. 6 Ancrenaz, M., Gumal, M., Marshall, A.J., Meijaard, E., Wich, S.A., and Husson, S. (2016). Pongo pygmaeus. The IUCN Red List of Threatened Species 2016, e.T17975A17966347. https://doi.org/10.2305/IUCN.UK.2016-1.RLTS.T17975A17966347.en. 7 Singleton, I., Wich, S.A., Nowak, M., Usher, G., and Utami-Atmoko, S.S. (2017). Pongo abelii. The IUCN Red List of Threatened Species 2017, e.T121097935A115575085. https://doi.org/10.2305/IUCN.UK.2016-1.RLTS.T17975A17966347.en. We applaud the Indonesian conservation authorities for providing publicly available documentation on forest management impacts, and for their use of quantitative measures of wildlife conservation progress []. Based on the above-mentioned discrepancy, however, we question whether appropriate methods and efforts were employed to assess management impacts on wildlife trends. For orangutan impact monitoring, the Indonesian government reported on nine monitoring sites, including national parks for which the 2015 population was established to be 1,153 orangutans []. By 2016, the government estimated that these sampled populations had more than doubled to 2,451 individuals []. There are three major issues with this reported population trend. First, it is biologically impossible for an orangutan population to double its size in a year []. Second, some of the government-sampled sites are used for orangutan introductions or translocations from other sites (for example, Bukit Baka–Bukit Raya National Park), implying that any net positive change in the monitored sites was inevitably preceded by at least an equally large negative change in non-monitored populations from which orangutans had been initially removed. Third, the nine government sampling plots and their reported populations represent less than 5% of the Bornean and Sumatran orangutan ranges, and zero percent of the Tapanuli orangutan range. Furthermore, all monitoring sites are within protected areas, whereas the majority of orangutans occur in non-protected lands []. It is thus scientifically unjustified to extrapolate population trends from these sampling sites to the total range of all three species.

1 Ministry of Environment and Forestry Republic of Indonesia (2018). The State of Indonesia’s Forests 2018. (Jakarta: Ministry of Environment and Forestry, Republic of Indonesia), p. 157. www.menlhk.go.id/downlot.php?file=SoiFo.pdf. 10 Payne, J., and Yoganand, K. (2017). Critically Endangered Sumatran Rhinoceros: Inputs for Recovery Strategy and Emergency Actions 2017–2027. (Kota Kinabalu: World Wildlife Fund). https://d2d2tb15kqhejt.cloudfront.net/downloads/critically_endangered_sumatran_rhinoceros.pdf. The apparent mismatch between reported and achievable population growth for orangutans is not limited to this species alone. Indeed, the report states that populations of 19 of the Indonesian government’s 25 priority species also grew by more than 10% []. This is not possible for some of the listed species, such as the Sumatran rhinoceros (Dicerorhinus sumatrensis), given known breeding rates and threat levels. For the past several decades overall Sumatran-rhinoceros birth rates have been exceeded by death rates [].

We acknowledge the difficulty of accurately estimating population trends for elusive, low-density species such as orangutans. However, we believe that the current Indonesian government methods provide an unrealistically positive and biased picture of orangutan population trends. The direct measurements of orangutan numbers could, for example, be complemented with an assessment of changes in their forest habitat, which would offer a more robust estimate of their current status. Establishing targets such as an increase in the percentage of orangutan habitat that is protected or well managed, including not only forest management but also the implementation of zero-killing policies, might allow easier verification of progress towards established goals.