Determination of ape distribution and population size using ground and aerial surveys: a case study with orang-utans in lower Kinabatangan, Sabah, Malaysia

Authors

  • Marc Ancrenaz,

    Corresponding author
    1. Kinabatangan Orangutan Conservation Project, PO Box 3109, 90734 Sandakan, Sabah, Malaysia
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  • Benoit Goossens,

    1. Kinabatangan Orangutan Conservation Project, PO Box 3109, 90734 Sandakan, Sabah, Malaysia
    2. Institute for Tropical Biology and Conservation, Universiti Malaysia Sabah, Locked Bag 2073, 88000 Kota Kinabalu, Sabah, Malaysia
    3. Biodiversity and Ecological Processes Group, Cardiff School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK
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  • Olivier Gimenez,

    1. CEFE/CNRS; 1919, Route de Mende; 34293 Montpellier-Cedex 5, France
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  • Azri Sawang,

    1. Kinabatangan Orangutan Conservation Project, PO Box 3109, 90734 Sandakan, Sabah, Malaysia
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  • Isabelle Lackman-Ancrenaz

    1. Kinabatangan Orangutan Conservation Project, PO Box 3109, 90734 Sandakan, Sabah, Malaysia
    2. Pittsburgh Research Fellowship, Pittsburgh Zoo
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*All correspondence to: Marc Ancrenaz: KOCP, Austral Park, Lorong 10, House Number 35, 88300 Kota Kinabalu, Sabah, Malaysia. Tel/Fax: 60 88 250 540; E-mail: hutan1@tm.net.my

Abstract

Because of the difficulties encountered in detecting many large tropical forest-dwelling species in their natural habitat, precise figures concerning the distribution, number and trends of many populations remain deficient. In tropical forests, ground surveys are generally carried out by counting objects along straight lines. These counts require a strict compliance with the line-transect methodology before (proper design of the census), during (careful data collection) and after (accurate and correct data processing and analysis) the census itself. In addition, the major source of bias when estimating population size and/or trends comes from the extrapolation of estimates obtained in small sampling areas to the larger, and often incompletely known, distribution of the population. In the Kinabatangan floodplain (Sabah, Malaysia), helicopter surveys were useful in directly assessing the distribution of orang-utans and were a major advantage in the precise estimation of the size of the orang-utan population surviving in this region. Our survey showed that about 1100 orang-utans remain in the multiple-use forests of the Kinabatangan floodplain. These results provide new evidence on orang-utan adaptation to habitat disturbance and indicate the potential of the Kinabatangan multiple-use forests for orang-utan conservation. Helicopter surveys appear to be a promising alternative to ground survey for precise distribution assessment and for monitoring population trends of apes throughout their entire range in Asia and in some parts of Africa.

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