Changes to Sabah’s orangutan population in recent times: 2002–2017

Abstract

The Bornean orangutan is critically endangered and monitoring its population is needed to inform effective conservation management. In this paper, we present results of 2014–17 aerial nest surveys of the major orangutan populations in Sabah and compare them with baseline data produced during surveys conducted in 2002–03 using similar methods. Our results show three important points: a) by increasing the survey effort (estimated at 15–25% cover), sparsely scattered orangutan sub-populations not recorded in the previous aerial surveys were located and the accuracy of the nest count estimates is expected to improve; b) large populations in the interior forests of Sabah, occupying sustainably managed logged and unlogged forests, have been stable over 15 years and are of vital importance for the species’ conservation; c) fragmented populations located in eastern Sabah, that are surrounded by extensive oil palm plantations, have declined at varying rates.

No time to rest: How the effects of climate change on nest decay threaten the conservation of apes in the wild

“…In recent years, some studies have included survey-specific decay time by either observation [ 48 , 79 , 80 , 82 ] or modelling [ 38 , 53 , 54 , 81 , 92 – 95 ]. Others have incorporated values obtained in the same area from an earlier survey [ 51 , 55 , 96 – 99 ], from a site close to the surveyed area [ 34 , 50 , 58 , 60 , 99 , 100 ], or from averaged published values [ 101 ]. Our findings highlight the problematic nature of this approach.…”

“…However, camera-trap methods have not yet been fully validated and they require costlier equipment than nest count methods. Thus, nest count surveys remain highly relevant, with SCNC being the most commonly used method for estimating ape density in the wild, both via traditional ground [47][48][49][50] or aerial [51,52] line transects. Finally, to investigate population trends, a crucial body of information in conservation science, it is necessary to compare estimates of ape population density obtained at different points in time [53][54][55][56].…”

“…However, as such studies could last several months, more time-efficient methods have been developed, such as the retrospective estimation of nest decay with a single revisit of a marked nest, using logistic regression [57], or hidden Markov chain [58] analysis. Nevertheless, with the exception of some authors who have modelled decomposition time across sites [53,54], published decay times have been applied to different sites [34,56,[59][60][61] and/or time periods [51,62]. This is problematic, as nest decomposition may differ with differing climate conditions, leading to inaccurate population density estimates [56,63].…”

Impact of Malaysian palm oil on sustainable development goals: co-benefits and trade-offs across mitigation strategies

“…Currently, although HCV assessments have been found to be beneficial, lack of monitoring indicators for plantations managers was identified as a barrier to efficient HCV implementation (Pillai 2020). Encouragingly, the Malaysian Palm Oil Green Conservation Fund (MPOGC) was incorporated on 19 February 2020 to support conservation projects such as the planting of 1 million forest trees in Lahad Datu, Sabah and the Orangutan Population Census and Pygmy Elephants program, a collaboration between the Malaysian Palm Oil Council (MPOC) and the Sabah State Government (Azian et al 2020), which leverages on data highlighting the need to support these species in fragmented areas (Simon et al 2019).…”

Envisioning a future for Bornean orangutans: Conservation impacts of action plan implementation and recommendations for improved population outcomes

“…However, protected areas have increased, most notably within Sabah and Sarawak, Malaysia, and in Central Kalimantan. The Malaysian states of Sabah and Sarawak have decided to fully protect most of the orangutan range as a conservation strategy, and the recent surveys show the populations in these two states are becoming stable (Simon et al 2019), except in non-protected or in fragmented forests. The network of fully protected forests in Kalimantan is smaller relative to forest extent and the prevalence of detected illegal activities (see Results sections on Rescue and release, and Law enforcement).…”