Counting Sunda clouded leopards with confidence: incorporating individual heterogeneity in density estimates

Azlan Mohamed,Andreas Wilting,Johnny Kissing,Rahel Sollmann,Jürgen Niedballa,Seth Timothy Wong,Jesse F Abrams

doi:10.1017/s0030605318001503

Abstract

AbstractEven with intensive sampling effort, data often remain sparse when estimating population density of elusive species such as the Sunda clouded leopard Neofelis diardi. An inadequate number of recaptures can make it difficult to account for heterogeneity in detection parameters. We used data from large-scale camera-trapping surveys in three forest reserves in Sabah, Malaysian Borneo, to (1) examine whether a high-density camera-trap network increases the number of recaptures for females, which tend to be more difficult to detect, thus improving the accuracy of density estimates; (2) compare density estimates from models incorporating individual heterogeneity in detection parameters with estimates from the null model to evaluate its potential bias; and (3) investigate how the size of the camera-trap grid affects density and movement estimates. We found that individual heterogeneity could not be incorporated in the single-site data analysis and only conservative null model estimates could be generated. However, aggregating data across study sites enabled us to account for individual heterogeneity and we estimated densities of 1.27–2.82 individuals/100 km2, 2–3 times higher than estimates from null models. In light of these findings, it is possible that earlier studies underestimated population density. Similar densities found in well-managed forest and recently selectively logged forest suggest that Sunda clouded leopards are relatively resilient to forest disturbances. Our analysis also revealed that camera-trapping grids for Sunda clouded leopard density estimations should cover large areas (c. 250 km2), although smaller grids could be appropriate if density or detectability are higher.

Highlights

The Sunda clouded leopard Neofelis diardi occurs in the tropical forests of Borneo and Sumatra
Its precise geographical range is unknown, but forest cover data suggest the species could still be widespread in Borneo, in the island’s central forest block, whereas in Sumatra its distribution is probably restricted to the west and a few isolated areas in the eastern and central parts of the island (Hearn et al, )
The Sunda clouded leopard is categorized as Vulnerable on The IUCN Red List of Threatened Species (Hearn et al, ), with its Bornean and Sumatran subspecies categorized as Endangered (Hearn et al, ; Sunarto et al, )

Summary

Introduction

The Sunda clouded leopard Neofelis diardi occurs in the tropical forests of Borneo and Sumatra. Effective conservation management for the Sunda clouded leopard is hampered by the lack of essential information about the species’ biology, population status and ability to survive in human-modified landscapes, within logging concessions, where a large proportion of its remaining population probably occurs (Wilting et al, ; Hearn et al, ). This dearth of information is mainly a result of the species’ partially nocturnal and elusive behaviour and low population densities Cheyne et al ( ) used a conventional capture–recapture model, which often overestimates densities, for wide-ranging species, because animal movements and the

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