Assessing detection probabilities for the endangered growling grass frog (Litoria raniformis) in southern VictoriaGeoffrey W. Heard A B D , Peter Robertson A and Michael P. Scroggie C
A Wildlife Profiles Pty Ltd, PO Box 500, Heidelberg, Vic. 3084, Australia.
B Present address: Department of Zoology, La Trobe University, Bundoora, Vic. 3086, Australia.
C Arthur Rylah Institute for Environmental Research, PO Box 137, Heidelberg, Vic. 3084, Australia.
D Corresponding author. Email: email@example.com
Wildlife Research 33(7) 557-564 https://doi.org/10.1071/WR04080
Submitted: 16 September 2004 Accepted: 2 August 2006 Published: 15 November 2006
Assessment of the efficacy of survey techniques for determining species occurrence is crucial for the validation of wildlife survey data. We analysed repeated site-survey data for adults and larvae of the growling grass frog (Litoria raniformis) in order to estimate probabilities of detection for the species using alternative survey techniques. The estimated probability of detecting adults of L. raniformis at occupied sites using diurnal searches was much less than 1.0 (0.107; 95% credible interval: 0.045, 0.192). The estimated probability of detecting adults using nocturnal spotlight searches was considerably higher, but still less than 1.0 (0.696; 95% credible interval: 0.585, 0.796). These results indicate that nocturnal searches are a much more efficient and reliable means of detecting the presence of adult L. raniformis than diurnal searches, but detection using either technique is less than certain. The probability of detecting tadpoles of L. raniformis using either funnel-trapping or dip-netting techniques was estimated at 0.350 (95% credible interval: 0.151, 0.567). Together, these results indicate that reliance on single-site visits during surveys for this species is likely to result in severe under-estimation of the proportion of sites that are actually occupied. We urge other workers to use repeated site-survey data and appropriate methods of data analysis to assess and report probabilities of detection when documenting the results of wildlife surveys.
For assistance in the field we are grateful to Lawrie Conole, Emma Moysey and Sarah Way (all Ecology Australia Pty Ltd), Leigh Ahern (Nature Scope Pty Ltd), Heath Butler, Ben North and Katie Howard (all Department of Zoology, La Trobe University), Wendy Moore (Friends of Craigieburn Grasslands), Jeremy Tscharke (Parks Victoria) and Rob Valentic. For loan of funnel-traps we are particularly indebted to John McGuckin (Streamline Research Pty Ltd). Several landholders provided access to private property. In particular, we are grateful to Steve Rogers (Pioneer Landfill) for access to the Wollert landfill site. Graeme Gillespie, Nick Clemann (DSE), Aaron Organ (Biosis Research Pty Ltd), Gerry Marantelli (Amphibian Research Centre), Brian Malone and Garry Peterson (La Trobe University) provided useful discussion during the project. Helpful discussions with Brendan Wintle (University of Melbourne) and Darryl MacKenzie (Proteus Research and Consulting Ltd, Dunedin, New Zealand) are gratefully acknowledged. We thank Eve McDonald-Madden, Nick Clemann, Deirdre Lucas and two anonymous reviewers for their comments on earlier drafts of this manuscript. This study was undertaken pursuant to the provisions of the Victorian Wildlife Act 1975, in accordance with the conditions of research permit no. 10001816. Funding was provided by the Victorian Department of Sustainability and Environment, and Yarra Valley Water.
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