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Open AccessArticle

Drivers of Bornean Orangutan Distribution across a Multiple-Use Tropical Landscape

1
School of Biological Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK
2
Department of Biology, University of Ottawa, Gendron Hall, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada
3
South East Asia Rainforest Research Partnership, Danum Valley Field Centre, P.O. Box 60282, Lahad Datu 91112, Sabah, Malaysia
4
Institute for Tropical Biology and Conservation, Universiti Malaysia Sabah, Jalan UMS, Kota Kinabalu 88400, Sabah, Malaysia
5
Asian School of the Environment, Nanyang Technological University, 50 Nanyang Avenue Singapore, Singapore 639798, Singapore
6
Division of Biological Sciences & Wildlife Biology Program, University of Montana, Missoula, MT 59812, USA
7
School of Biological and Environmental Sciences, Liverpool John Moores University, Exchange Station, Liverpool L2 2QP, UK
*
Author to whom correspondence should be addressed.
Academic Editor: Lin Cao
Remote Sens. 2021, 13(3), 458; https://doi.org/10.3390/rs13030458
Received: 15 December 2020 / Revised: 22 January 2021 / Accepted: 25 January 2021 / Published: 28 January 2021
(This article belongs to the Special Issue Drone-Based Ecological Conservation)
Logging and conversion of tropical forests in Southeast Asia have resulted in the expansion of landscapes containing a mosaic of habitats that may vary in their ability to sustain local biodiversity. However, the complexity of these landscapes makes it difficult to assess abundance and distribution of some species using ground-based surveys alone. Here, we deployed a combination of ground-transects and aerial surveys to determine drivers of the critically endangered Bornean Orangutan (Pongo pygmaeus morio) distribution across a large multiple-use landscape in Sabah, Malaysian Borneo. Ground-transects and aerial surveys using drones were conducted for orangutan nests and hemi-epiphytic strangler fig trees (Ficus spp.) (an important food resource) in 48 survey areas across 76 km2, within a study landscape of 261 km2. Orangutan nest count data were fitted to models accounting for variation in land use, above-ground carbon density (ACD, a surrogate for forest quality), strangler fig density, and elevation (between 117 and 675 m). Orangutan nest counts were significantly higher in all land uses possessing natural forest cover, regardless of degradation status, than in monoculture plantations. Within these natural forests, nest counts increased with higher ACD and strangler fig density, but not with elevation. In logged forest (ACD 14–150 Mg ha−1), strangler fig density had a significant, positive relationship with orangutan nest counts, but this relationship disappeared in a forest with higher carbon content (ACD 150–209 Mg ha−1). Based on an area-to-area comparison, orangutan nest counts from ground transects were higher than from counts derived from aerial surveys, but this did not constitute a statistically significant difference. Although the difference in nest counts was not significantly different, this analysis indicates that both methods under-sample the total number of nests present within a given area. Aerial surveys are, therefore, a useful method for assessing the orangutan habitat use over large areas. However, the under-estimation of nest counts by both methods suggests that a small number of ground surveys should be retained in future surveys using this technique, particularly in areas with dense understory vegetation. This study shows that even highly degraded forests may be a suitable orangutan habitat as long as strangler fig trees remain intact after areas of forest are logged. Enrichment planting of strangler figs may, therefore, be a valuable tool for orangutan conservation in these landscapes. View Full-Text
Keywords: aboveground carbon; aerial survey; drone; forest disturbance; ground-transect; land use; multiple-use landscape; strangler fig aboveground carbon; aerial survey; drone; forest disturbance; ground-transect; land use; multiple-use landscape; strangler fig
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MDPI and ACS Style

Milne, S.; Martin, J.G.A.; Reynolds, G.; Vairappan, C.S.; Slade, E.M.; Brodie, J.F.; Wich, S.A.; Williamson, N.; Burslem, D.F.R.P. Drivers of Bornean Orangutan Distribution across a Multiple-Use Tropical Landscape. Remote Sens. 2021, 13, 458. https://doi.org/10.3390/rs13030458

AMA Style

Milne S, Martin JGA, Reynolds G, Vairappan CS, Slade EM, Brodie JF, Wich SA, Williamson N, Burslem DFRP. Drivers of Bornean Orangutan Distribution across a Multiple-Use Tropical Landscape. Remote Sensing. 2021; 13(3):458. https://doi.org/10.3390/rs13030458

Chicago/Turabian Style

Milne, Sol; Martin, Julien G.A.; Reynolds, Glen; Vairappan, Charles S.; Slade, Eleanor M.; Brodie, Jedediah F.; Wich, Serge A.; Williamson, Nicola; Burslem, David F.R.P. 2021. "Drivers of Bornean Orangutan Distribution across a Multiple-Use Tropical Landscape" Remote Sens. 13, no. 3: 458. https://doi.org/10.3390/rs13030458

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