Register      Login
Wildlife Research Wildlife Research Society
Ecology, management and conservation in natural and modified habitats
Shopping Cart: ( empty )
You are here: Home > Journals > WR > WR03091
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.


References

Anon.  (1890). Orchard pests. New South Wales Agriculture Gazette, 105–107.

Augee, M. L. , and Ford, D. (1999). Radio-tracking studies of grey-headed flying-foxes, Pteropus poliocephalus, from the Gordon colony, Sydney. Proceedings of the Linnean Society of New South Wales 121, 61–70.
Bibby C. J., Burgess N. D., and Hill D. A. (1992). ‘Bird Census Techniques.’ (Academic Press: London.)

Brooke, A. P. , Solek, C. , and Tualaulelei, A. (2000). Roosting behavior of colonial and solitary flying foxes in American Samoa (Chiroptera: Pteropodidae). Biotropica 32, 338–350.
Caughley G. (1979). ‘Design for Aerial Census.’ (Australian Government Publishing Service: Canberra.)

Caughley, G. , and Grice, D. (1982). A correction factor for counting emus from the air, and its application to counts in Western Australia. Australian Wildlife Research 9, 253–259.
Caughley G., and Gunn A. (1996). ‘Conservation Biology in Theory and Practice.’ (Blackwell Science: Cambridge, MA.)

Cox P. A., Elinqvist T., Pierson E. D., and Rainey W. E. (1992). Flying-foxes as pollinators and seed dispersers in Pacific island ecosystems. In ‘Pacific Island Flying-foxes: Proceedings of an International Conservation Conference’. (Eds D. E. Wilson and G. I. Graham.) US Fish and Wildlife Botanical Report No. 90 (23). (US Department of the Interior, Fish and Wildlife Service: Washington, DC.)

Docteurs van Leeuwen, W. M. (1935). The dispersal of plants by fruit eating bats. Gardens Bulletin Straits Settlements 9, 58–63.
Eby P., and Lunney D. (2002). Managing the grey-headed flying-fox Pteropus poliocephalus as a threatened species: a context for the debate. In ‘Managing the Grey-headed Flying-fox Pteropus poliocephalus as a Threatened Species in NSW’. (Eds P. Eby and D. Lunney.) pp. 1–15. (Royal Zoological Society of NSW: Sydney.)

Eby, P. , Richards, G. , Collins, L. , and Parry-Jones, K. (1999). The distribution, abundance and vulnerability to population reduction of a nomadic nectarivore, the grey-headed flying-fox Pteropus poliocephalus in New South Wales, during a period of resource concentration. Australian Zoologist 31, 240–253.
Gibbons D. W., Hill D. A., and Sutherland W. J. (1996). Birds. In ‘Ecological Census Techniques: a Handbook’. (Ed. W. J. Sutherland.) pp. 227–259. (Cambridge University Press: Cambridge.)

Graham, A. , and Bell, R. (1989). Investigating observer bias in aerial survey by simultaneous double-counts. Journal of Wildlife Management 53, 1009–1016.
Greenwood J. J. D. (1996). Basic techniques. In ‘Ecological Census Techniques: a Handbook’. (Ed. W. J. Sutherland.) pp. 11–110. (Cambridge University Press: Cambridge.)

Halpin, K. , Young, P. L. , Field, H. E. , and Mackenzie, J. S. (2000). Isolation of Hendra virus from pteropid bats: a natural reservoir of Hendra virus. Journal of General Virology 81, 1927–1932.
IUCN (2002). 2002 IUCN Red List of Threatened Species. <http://www.redlist.org>. Downloaded on 14 August 2002.

Kress, J. W. (1985). Bat pollination of an Old World Heliconia. Biotropica 17, 302–308.
Mickelburg S. P., Racey P. A., and Hutson A. M. (1992). Old World fruit bats. An action plan for their conservation. International Union for the Conservation of Nature and Natural Resources.

Palmer, C. , and Woinarski, J. C. Z. (1999). Seasonal roosts and foraging movements of the black flying fox (Pteropus alecto) in the Northern Territory: resource tracking in a landscape mosaic. Wildlife Research 26, 823–838.
Radcliffe F. N. (1931). The flying-fox (Pteropus) in Australia. CSIR Bulletin No. 53.

Rappoldt, C. , Kersten, M. , and Smit, C. (1985). Errors in large-scale shorebird counts. Ardea 73, 13–24.
Spellerberg I. F. (1992). ‘Evaluation and Assessment for Conservation.’ (Chapman and Hall: London.)

Spencer, H. J. , Palmer, C. , and Parry-Jones, K. (1991). Movements of fruit-bats in eastern Australia, determined by using radio-tracking. Wildlife Research 18, 463–468.
Sullivan S. (2003). A report to QPWS, Cairns on the Annual Spectacled Flying Fox Census 2002. Townsville, QPWS.

Sutherland W. J. ((1996). The twenty commonest censusing sins. In ‘Ecological Census Techniques: a Handbook’. (Ed. W. J. Sutherland.) pp. 317–318. (Cambridge University Press: Cambridge.)

Thomas D. W. (1982). The ecology of an African savanna fruit bat community: resource partitioning and role in seed dispersal. Ph.D. Thesis, University of Aberdeen, Scotland.

Tidemann, C. R. , and Vardon, M. J. (1997). Pests, pestilence, pollen and protein: the need for community-based managemennt of flying-foxes in Australia. Australian Biologist 10, 79–85.
West C. (2002). Contemproary issues in managing flying-fox camps: a publicly-documented conflict from Maclean on the north coast of NSW. In ‘Managing the Grey-headed Flying-fox Pteropus poliocephalus as a Threatened Species in NSW’. (Eds P. Eby and D. Lunney.) pp. 176–195. (Royal Zoological Society of NSW: Sydney.)

Westcott D. A., Dennis A. J., McKeown A., Bradford M. G., and Margules C. R. (2001). The spectacled flying-fox, Pteropus conspicillatus, in the context of the World Heritage values of the Wet Tropics World Heritage Area. A peer-reviewed report to Environment Australia.

Whybird O. (2000). Report to the Wildlife Preservation Society, Brisbane on the spectacled flying fox survey.

Wiles, G. J. , Lemke, T. O. , and Payne, N. H. (1989). Population estimates of fruit bats (Pteropus mariannus) in the Mariana Islands. Conservation Biology 3, 66–76.


Wiles, G. J. , Engbring, J. , and Otobed, D. (1997). Abundance, biology, and human exploitation of bats in the Palau Islands. Journal of Zoology 241, 203–227.