Andreas Wilting, Frauke Fischer, K. Eduard Linsenmair
Address (University of Würzburg, Biocentre, Department of Animal Ecology and
Tropical Biology 97074 Würzburg, Germany)
Corresponding author Andreas Wilting
Phone: +49-931-888 4316
Fax: +49-931-888 4352
Email: a.wilting@gmx.de
In our recent paper [2] we proposed the potential of a rigorous track classification method to study even secretive carnivores in tropical rainforest. In addition we estimated on the basis of six clouded leopard track sets a rough minimum density of clouded leopards in our small study area and extrapolated our local results to the landscape level.
We are grateful for the critical response by Gordon et al., but would like to emphasise, that we are fully aware of the limitations of the track classification method. Our extrapolated clouded leopard numbers were rather intended to be a first working hypothesis for further research than a reliable estimation of the actual population size in the whole State of Sabah.
We would like to respond to the main concerns of Gordon et al. to clarify our results and help to prevent misinterpretations that might have negative effects on the management of one of the most threatened cat species in Asia.
Gordon et al. pointed out that in our study only two of six pugmark-sets fulfil the criteria by Sharma et al. [11] of a minimum number of pugmarks within a pugmarkset. However Sharma et al. [11] showed that a minimum of 4 pugmarks per pugmark-set led to a classification accuracy of over 90 %. They suggested including at least 10 pugmarks per pugmark-set when in total c. 20 pugmark-sets are used in the analysis to obtain an even higher certainty [11]. We believe that the lower number of pugmark-sets in our study and the large distances between the principal component loadings of the different pugmark-sets allowed us to work with a smaller number of pugmarks without sacrificing the high level of reliability. Therefore we feel safe to presume a minimum number of four clouded leopards in our study site.
Correctly Gordon et al. pointed out, that it is extremely difficult to recognise individual felids from their tracks. Therefore, we noted that further studies have to ensure that the study areas have to be small and contain only a few individuals of the target species. We also noted that only a small fraction of the entire population can be distinguished by their tracks and that calculated abundances should always be treated as minimum numbers, because even in small populations two animals might have very similar track measurements and cannot be separated by a multivariate analysis with certainty.
Gordon et al. are right to emphasise the differing suitability of substrates to exactly mirror the individual properties of pugmarks as a crucial factor in the application of the track classification method. We explicitly stressed that different substrates will affect the size of tracks significantly, causing wrong measurements. During our study the substrates and their decisive properties, especially soil type, humidity and substrate depth were very similar in the different track sets. Thus we believe that the substrate did not bias our results. Gordon et al. first suggested reducing our sample size, because only two pugmark-sets meet the strict requirements by Sharma et al. [11], but later they criticised that by excluding eight pugmark-sets additional individuals might not have been detected. We agree that the exclusion of these pugmark-sets might affect our results, but the inclusion of pugmark-sets, which first could not even be allocated without doubt to clouded leopards and secondly were found on substrates differing from those of the other pugmark-sets would bias our results even more. To track all individuals in a study site can never be guaranteed by pugmark assessment. Therefore we applied a capture-recapture analysis to estimate the actual population size. Due to the low number of recaptures in our study we emphasised that our calculated density should rather be taken as a rough minimum estimate and not as the true number. We did not distinct between the sexes and various age groups, because for example differentiation between sub-adult male pugmarks and adult female tracks is extremely difficult. Therefore we believe that the track surveys cannot provide information about sex and age of the individuals with a high certainty. Nevertheless, we suppose, fully in line with previous methodological publications [e. g. 9, 11, 13-15], that the track classification method will have a high potential for further research activities as long as the limitations of this method are well considered.
Furthermore Gordon et al. criticized that we up-scaled our local results to the landscape level. We are equally concerned and well aware of the fact that without any detailed information about the other areas such extrapolations are based on very weak evidence. We discussed the problems resulting from this approach in our publication (different legal hunting and poaching pressures; different forest structures and protection status of the reserves, and different prey abundances in the reserves). The authors are right that the close proximity of our study site to the delimitated oil palm plantation affect the density of potential prey species, but without any information about the extent of regional differences and without any knowledge about clouded leopards preferable prey species in Borneo, we were not able to consider this in our rough calculation. Being aware of all these uncertainties we still suppose that as a first working hypothesis these figures are of great value for future research projects. It is a first tentative step to fill a tremendous knowledge gap. For a species with such limited information available concerning its distribution and status, even very rough estimates, based on limited data, are valuable and important.
Gordon et al. are right in stating that these numbers should not become a “quoted fact” in literature. They should rather motivate researches to test these numbers during intensive field studies and help to set priorities for future research plans. These upcoming research activities are of even greater importance, because recent reclassification of clouded leopards suggests a distinct species (N. diardi) on the Sundaland islands Borneo and Sumatra [8, 24, 25]. Furthermore a wider genetic sampling by Wilting et al. [25] indicates limited gene flow and population division between the islands of Borneo and Sumatra. This reclassification puts Bornean clouded leopards under an even greater risk of extinction.
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