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RESEARCH ARTICLE
Contents Vol 31(5)

Observer error in exit counts of flying-foxes (Pteropus spp.)

David A. Westcott A B and Adam McKeown A
+ Author Affiliations
- Author Affiliations

A CSIRO Sustainable Ecosystems and the Rainforest CRC, Tropical Forest Research Centre, PO Box 780, Atherton, Qld 4883, Australia.

B Corresponding author. Email: david.westcott@csiro.au

Wildlife Research 31(5) 551-558 https://doi.org/10.1071/WR03091
Submitted: 23 September 2003  Accepted: 24 June 2004   Published: 13 December 2004

Abstract

Population estimation and monitoring is a fundamental component in the conservation management of any species. For species such as flying-foxes (Pteropus spp.) population estimation is complicated by the large number of animals involved, their mobility and the conditions under which counts are conducted. Because count results are used in the determination of management requirements, they are the focus of much critical attention. Despite this, while measures of the precision of fly-out counts of Pteropus spp. have been published, measures of their accuracy have not. In this paper we present an assessment of the accuracy and precision of observer counts of dusk fly-outs by comparing recordings of observers’ counts with a video of the same fly-out. Observer’s counts were significantly related to the video-count (rs = 0.69, P < 0.0001), with the average observer’s count underestimating the video-count by 14.7% (± 25, s.d.) of the video-count. Observers’ errors increased with the rate at which flying-foxes left the camp and with the width of the fly-out stream. These results suggest that while observers’ errors are inherent in dusk fly-out counts, these errors are manageable and relatively predictable. Other sources of error are likely to have a greater impact on the final population estimate at both camp and regional scales.


Acknowledgments

First and foremost, our thanks go to the volunteers who came and counted for us and bore with us through the procedure. Stephen Garnett was a fine guinea-pig and enthusiastically urged us on. Bronwyn Bayly assisted in the early counts as a volunteer wrangler and, along with Matt Bradford, assisted with counting bats on video-recordings. We thank Stephen Garnett and Nigel Weston for their critiques of earlier drafts of the manuscript.


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