Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2005 Jan;3(1):e3.
doi: 10.1371/journal.pbio.0030003. Epub 2004 Dec 7.

Aerial surveys give new estimates for orangutans in Sabah, Malaysia

Marc Ancrenaz  1 , Olivier Gimenez, Laurentius Ambu, Karine Ancrenaz, Patrick Andau, Benoît Goossens, John Payne, Azri Sawang, Augustine Tuuga, Isabelle Lackman-Ancrenaz
Affiliations

Aerial surveys give new estimates for orangutans in Sabah, Malaysia

Marc Ancrenaz et al. PLoS Biol. 2005 Jan.

Abstract

Great apes are threatened with extinction, but precise information about the distribution and size of most populations is currently lacking. We conducted orangutan nest counts in the Malaysian state of Sabah (North Borneo), using a combination of ground and helicopter surveys, and provided a way to estimate the current distribution and size of the populations living throughout the entire state. We show that the number of nests detected during aerial surveys is directly related to the estimated true animal density and that a helicopter is an efficient tool to provide robust estimates of orangutan numbers. Our results reveal that with a total estimated population size of about 11,000 individuals, Sabah is one of the main strongholds for orangutans in North Borneo. More than 60% of orangutans living in the state occur outside protected areas, in production forests that have been through several rounds of logging extraction and are still exploited for timber. The role of exploited forests clearly merits further investigation for orangutan conservation in Sabah.

PubMed Disclaimer

Conflict of interest statement

The authors have declared that no conflicts of interest exist.

Figures

Figure 1
Figure 1. Distribution and Size of the 16 Major Orangutan Populations Identified during the Surveys in Sabah, Malaysia, Borneo
Figure 2
Figure 2. Location of Ground and Aerial Surveys during the Orangutan Census in Sabah, Malaysia, Borneo
Aerial transects are not shown for the Lower Kinabatangan forests.
Figure 3
Figure 3. Graph Showing the Predicted Orangutan Nest Density as a Function of Aerial Indexes
The plain line is the fitted line via model (5), and dashed lines are prediction intervals; n = 13 sites, 2 observers.
See this image and copyright information in PMC

References

    1. Rijksen HD, Meijaard E. Our vanishing relative. Dordrecht: Kluwer Academic; 1999. 480 pp.
    1. van Schaik CP, Monk KA, Robertson JMY. Dramatic decline in orangutan numbers in the Leuser Ecosystem, Northern Sumatra. Oryx. 2001;35:14–25.
    1. Sugardjito J. Conservation of orangutans: Threats and prospects. In: Nadler RD, Galdikas BFM, Sheeran LK, Rosen N, editors. The neglected ape. New York: Plenum Press; 1995. pp. 45–49.
    1. Tutin CEG, Fernandez M. Nationwide census of gorilla and chimpanzee populations in Gabon. Am J Primatol. 1984;6:313–336. - PubMed
    1. van Schaik CP, Priatna A, Priatna D. Population estimates and habitat preferences of orangutans (Pongo pygmaeus) based on line transects of nests. In: Nadler RD, Galdikas BFM, Sheeran LK, Rosen N, editors. The neglected ape. New York: Plenum Press; 1995. pp. 129–147.

Publication types