Sungai Wain Protected Forest (Gibbon)

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Summary

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• Müller’s gibbons (Hylobates muelleri) are present in Sungai Wain Protected Forest.
• The population size is around 531 gibbons.
• The gibbon population trend is unknown.
• The site has a total size of 112.45 km².
• The main reported threats include recurring wildfires and illegal logging activities.
• Conservation efforts have primarily focused on habitat protection, restricting the number of people accessing the site, and conducting anti-poaching and anti-logging patrols.

Site characteristics

The Sungai Wain Protection Forest, located near Balikpapan Borneo's fourth largest city is a unique and ecologically significant area. Roughly half of it remains pristine coastal lowland dipterocarp rainforest, hosting the full range of native forest species typical of this habitat. Although a devastating fire in 1998 scorched around 40% of the forest, successful fire prevention efforts have helped the area recover, despite a setback when approximately 830 hectares were burned again during the 2015 El Niño. The forest continues to provide vital habitat for species that are unique to Borneo, including the endemic Hylobates muelleri (Müller’s gibbon) (The Rufford Foundation 2017).

Table 1. Basic site information for Sungai Wain Protected Forest (Gibbon)

Species	Hylobates muelleri
Area	112.45 km²
Coordinates	Lat: -1.1 , Lon: 116.85
Type of site	Protected area (Protection Forest)
Habitat types	Subtropical/tropical moist lowland forest
Type of governance

Types of sites Governance types Habitat types

Ape status

Table 2. Ape population estimates reported for Sungai Wain Protected Forest (Gibbon)

Species	Year	Total number groups (95% CI)	Density ​​[groups/km²​] (95% CI)	Total number indiv. (95% CI)	Area	Method	Source	Comments	A.P.E.S. database ID
Hylobates muelleri	2012		4.6	531.1	Sungai Wain Protected Forest	Point transects, Fixed point triangulation	Gilhooly et al. 2015	The analysis was conducted using a combination of Distance sampling and Acoustic spatial capture-recapture methodologies.

Sampling methods Analytical frameworks

Threats

Table 3. Threats to apes reported for Sungai Wain Protected Forest (Gibbon)

Category	Specific threats	Threat level	Description	Year of threat
5 Biological resource use	5.3 Logging & wood harvesting	Present (unknown severity)	Since the 1970s, the eastern section of the forest has experienced degradation due to unlawful tree logging activities and the transformation of land into garden plots (Gilhooly et al. 2015).	1970-Ongoing (2015)
7 Natural system modifications	7.1 Fire & fire suppression	High (more than 70% of population affected)	The paper states that approximately 60% of the forest was affected by the 1998 fires, leaving only 40% as 'pristine forest.' This event led to habitat degradation, particularly in the regenerating forest, where tree diversity and density remain low potentially affecting gibbon density and distribution (Gilhooly et al. 2015).	1998-2015

Threats

Conservation activities

Table 4. Conservation activities reported for Sungai Wain Protected Forest (Gibbon)

Category	Specific activity	Description	Implementing organization(s)	Year of activity
2 Counter-wildlife crime	2.3 Conduct regular anti-poaching patrols	Anti-poaching and anti-logging patrols are ongoing in the reserve (Hutan Lindung Sungai Wain 2015).		Ongoing (2015)
5 Protection & restoration	5.2 Legally protect ape habitat	Sungai Wain Protected Forest has been designated as a protected forest since 1983; prior to that, it was established as a water catchment reserve in 1947 (Nijman and Menken 2005).		1983-Ongoing (2026)
5 Protection & restoration	5.8 Restrict number of people that are allowed access to site	Due to ongoing patrolling and enforcement efforts, access to the pristine area is tightly regulated and restricted to only authorized researchers and approved visitors (Gilhooly pers. obs. 2012).		Ongoing (2015)

Conservation activities

Enablers

Table 6. Enablers reported for Sungai Wain Protected Forest (Gibbon)

Enablers	Specific enablers	Source	Year(s)
4 Institutional support	4.1 Effective legislation and law enforcement	Harrison 2011	2002-Ongoing (2015)
5 Ecological context	5.1 Ecological characteristics (e.g. terrain) conducive to conservation	Gilhooly et al. 2015	Ongoing (2015)

Enablers

Documented behaviours

Table 7. Behaviours documented for Sungai Wain Protected Forest (Gibbon)

Category	Behavior	Observation type	Prevalence	Observation dates	Source	Habituation	Species	Comment
	Vocalizations: The duet songs of bonded gibbon pairs serve to mark territory and are also central to the survey methodology—triangulation via acoustic detection.				Gilhooly et al. 2015
	Duetting Behavior.				Gilhooly et al. 2015

Behaviours

References

Gilhooly, L. J., Rayadin, Y., & Cheyne, S. M. (2015). A comparison of hylobatid survey methods using triangulation on Müller’s gibbon (Hylobates muelleri) in Sungai Wain Protection Forest, East Kalimantan, Indonesia. International Journal of Primatology, *36*, 477–491. https://doi.org/10.1007/s10764-015-9845-1
The Rufford Foundation. (2017, May 5). Primate population monitoring in the Sungai Wain Protection Forest, East Kalimantan, Indonesia. Retrieved June 30, 2025, from https://www.rufford.org/projects/sugi-sugianto/primate-population-monitoring-in-the-sungai-wain-protection-forest-east-kalimantan-indonesia/
Nijman, V., & Menken, S. B. J. (2005). Assessment of census techniques for estimating density and biomass of gibbon (Primates: Hylobatidae). Raffles Bulletin of Zoology, 53, 201–211.
Harrison, R. D. (2011). Emptying the forest: Hunting and the extirpation of wildlife from tropical nature reserves. BioScience, 61, 919–924.
Hutan Lindung Sungai Wain. (2015). Pengelolaan HLSW. Retrieved from: http://sungaiwain.org/profil-hlsw/ pengelolaan-hlsw

Page created by: Aime Mizero Date: 2025-06-30