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RESEARCH ARTICLE
Contents Vol 34(8)

Cane toads reduce the abundance and site occupancy of Merten’s water monitor (Varanus mertensi)

Anthony D. Griffiths A B and J. Lindley McKay A
+ Author Affiliations
- Author Affiliations

A School for Environmental Research, Institute of Advanced Studies, Charles Darwin University, Darwin, NT 0909, Australia.

B Corresponding author. Present address: Biodiversity Conservation, Department of Natural Resources, Environment and the Arts, PO Box 496, Palmerston, NT 0831, Australia. Email: tony.griffiths@nt.gov.au

Wildlife Research 34(8) 609-615 https://doi.org/10.1071/WR07024
Submitted: 26 February 2007  Accepted: 8 October 2007   Published: 18 December 2007

Abstract

Introduced into Australia in 1935, the cane toad (Chaunus [Bufo] marinus) threatens native vertebrate predators. However, there have been few rigorous quantitative studies on species threatened by this toxic invasive species. This study examines the changes in abundance and proportion of sites occupied by Merten’s water monitor (Varanus mertensi) at a site in the Northern Territory following invasion by cane toads. The study was located at Manton Dam Recreation Area, 70 km south of Darwin, and ran for 18 months. Cane toads were first detected at the study site in February 2005, three months after the first survey, and their abundance remained low until February 2006, when an increase was observed. The abundance of V. mertensi declined substantially 8 months after the arrival of cane toads and remained low. The probability of detection of V. mertensi varied considerably within and among surveys, and was higher in the wet season surveys. The proportion of sites occupied by V. mertensi at the start of the study was 0.95 ± 0.03. Site occupancy remained high for 6 months after the arrival of cane toads, but declined gradually to a low of 0.15 ± 0.16 within 12 months. There has been demonstrable change in the abundance and proportion of sites occupied by V. mertensi following the colonisation of cane toads, but the population has been able to persist. Monitoring of populations impacted by cane toads may provide unique opportunities to understand processes underlying local extinction and colonisation of native predators following the impact of invasive species.


Acknowledgements

The project was funded by Parks and Wildlife Service of the Northern Territory and ARC Key Centre for Tropical Wildlife Management, Charles Darwin University. Numerous volunteers assisted with the fieldwork, including Steven Reynolds and Lauryn Cannon. Permission to undertake the study was granted by the Charles Darwin Animal Ethics Committee and the Parks and Wildlife Service NT. We thank Stephen Garnett and Peter Whitehead for their helpful comments.


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