title: Line Transect and Triangulation Surveys Provide Reliable Estimates of the Density of Kloss' Gibbons (Hylobates klossii) on Siberut Island, Indonesia.
abstract: Estimating population densities of key species is crucial for many conservation programs. Density estimates provide baseline data and enable monitoring of population size. Several different survey methods are available, and the choice of method depends on the species and study aims. Few studies have compared the accuracy and efficiency of different survey methods for large mammals, particularly for primates. Here we compare estimates of density and abundance of Kloss' gibbons (Hylobates klossii) using two of the most common survey methods: line transect distance sampling and triangulation. Line transect surveys (survey effort: 155.5 km) produced a total of 101 auditory and visual encounters and a density estimate of 5.5 gibbon clusters (groups or subgroups of primate social units)/km2. Triangulation conducted from 12 listening posts during the same period revealed a similar density estimate of 5.0 clusters/km2. Coefficients of variation of cluster density estimates were slightly higher from triangulation (0.24) than from line transects (0.17), resulting in a lack of precision in detecting changes in cluster densities of <66 % for triangulation and <47 % for line transect surveys at the 5 % significance level with a statistical power of 50 %. This case study shows that both methods may provide estimates with similar accuracy but that line transects can result in more precise estimates and allow assessment of other primate species. For a rapid assessment of gibbon density under time and financial constraints, the triangulation method also may be appropriate.
authors.affiliation: Department of Conservation Biology, Centre for Nature Conservation, Georg-August-Universität Göttingen, 37073 Göttingen, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Höing
authors.forename: Marcel C
authors.initials: MC
authors.lastname: Quinten
authors.forename: Yohana Maria
authors.initials: YM
authors.lastname: Indrawati
authors.forename: Susan M
authors.initials: SM
authors.lastname: Cheyne
authors.forename: Matthias
authors.initials: M
authors.lastname: Waltert
keywords: Auditory sampling; Hylobates klossii; Line transect survey; Mentawai islands; Siberut; Triangulation
references.citation: Folia Primatol (Basel). 1975;24(1):60-80
references.pmid: 1140755
references.citation: Am J Primatol. 2010 Jun;72(7):607-16
references.pmid: 20186760
references.citation: Primates. 2006 Oct;47(4):327-35
references.pmid: 16736263
references.citation: Primates. 2008 Jan;49(1):50-6
references.pmid: 17899314
references.citation: Am J Primatol. 1993;29(2):93-108
references.pmid: 31941194
references.citation: J Appl Ecol. 2010 Feb;47(1):5-14
references.pmid: 20383262
references.citation: Primates. 2006 Jan;47(1):65-73
references.pmid: 16132166