Density estimation of Asian bears using photographic capture-recapture sampling based on chest marks
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Author list: Ngoprasert D., Reed D.H., Steinmetz R., Gale G.A.
Publication year: 2012
Journal: Ursus (1537-6176)
Volume number: 23
Issue number: 2
Start page: 117
End page: 133
Number of pages: 17
ISSN: 1537-6176
Languages: English-Great Britain (EN-GB)
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Abstract
Assessing the conservation status of species of concern is greatly aided by unbiased estimates of population size. Population size is one of the primary parameters determining urgency of conservation action, and it provides baseline data against which to measure progress toward recovery. Asiatic black bears (Ursus thibetanus) and sun bears (Helarctos malayanus) are vulnerable to extinction, but no statistically rigorous population density estimates exist for wild bears of either species. We used a camera-based approach to estimate density of these sympatric bear species. First, we tested a technique to photograph bear chest marks using 3 camera traps mounted on trees facing each other in a triangular arrangement with bait in the center. Second, we developed criteria to identify individual sun bears and black bears based on chest-mark patterns and tested the level of congruence among 5 independent observers using a set of 234 photographs. Finally, we camera-trapped wild bears at 2 study areas (Khlong E-Tow, 33 km2, and Khlong Samor-Pun, 40 km2) in Khao Yai National Park, Thailand, and used chest marks to identify individual bears and thereby derive capture histories for bears of each species. Average congruence among observers' identifications of individual bears was 78.4% for black bear and 92.9% for sun bear across sites. At Khlong E-Tow, we recorded 13 black bears (8 M, 4 F, 1 unknown sex) and 8 sun bears (1 M, 5 F, 2 unknown sex). At Khlong Samor-Pun, we recorded 10 black bears (6 M, 4 F) and 6 sun bears (4 M, 2 F). We used a spatially explicit capture-recapture method, resulting in density estimates of 8.0 (SE = 3.04) and 5.8 (SE = 2.31) black bears per 100 km2 and 5.9 (SE = 3.07) and 4.3 (SE = 2.32) sun bears per 100 km 2 for each study area, respectively. Our camera trap design and chest-mark identification criteria can be used to estimate density of sun bears and black bears, enhancing knowledge of the conservation status of these threatened and little-known bear species. ฉ 2012 International Association for Bear Research and Management.
Keywords
Asiatic black bear, camera trapping, Helarctos malayanus, Khao Yai National Park, spatially-explicit capture-recapture, sun bear, Ursus thibetanus
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