Abstract
Effective conservation needs a solid baseline of animal distribution, density, and abundance data to base management strategies on and evaluate the effectiveness of conservation efforts on the species of interest. For many species it is not feasible to directly count individuals, and scientists are forced to use indirect methods that can provide estimates of density and abundance. For orangutans nest counts are the most often used indirect sign of presence. Models used for density and abundance estimates are based on a set of assumptions about the observations. Here we analyze the effect of several factors (distance to transect, height, decay stage, and observer experience) on the probability that an orangutan ( Pongo abelii) nest is found along a line transect. The results indicate that all factors significantly influence nest detection. Orangutan density estimates varied between the teams with the lowest estimate being approximately 83% of the highest estimate and orangutan density showed a positive correlation to experience level. We use these results to propose a new approach to determine orangutan density that should reduce variation between density estimates from nest surveys and therefore should lead to more reliable between-survey comparisons for orangutans and potentially other great-ape species.
Highlights
Key ingredients for conservation work are solid data on the density, abundance, and distribution of animal species
We analyze the effect of several factors on the probability that an orangutan (Pongo abelii) nest is found along a line transect
Orangutan density estimates varied between the teams with the lowest estimate being approximately 83% of the highest estimate and orangutan density showed a positive correlation to experience level
Summary
Key ingredients for conservation work are solid data on the density, abundance, and distribution of animal species. Because for most species it is not possible to directly count all individuals that occur in an area, scientists resort to methods that provide estimates for density and abundance without counting all individuals living in an area. To obtain data on great-ape density and abundance, nest counts have become the method of choice and are the recommended method in a recent best-practice guidelines document on great-ape census techniques by the IUCN [6]. From these counts, estimates of density and/or abundance can be derived following increasingly sophisticated models [1,7]. The critical assumption underlying the line transect method, regardless of which equation is used to account for missed nests, is that all nests located directly on the transect are found [8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
