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RESEARCH ARTICLE
Contents Vol 35(3)

Testing island biosecurity systems for invasive rats

James C. Russell A D , Brent M. Beaven B , Jamie W. B. MacKay A , David R. Towns C and Mick N. Clout A
+ Author Affiliations
- Author Affiliations

A School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.

B Stewart Island Field Centre, Department of Conservation, PO Box 3, Stewart Island 9846, New Zealand.

C Research, Development & Improvement Division, Department of Conservation, Private Bag 68908, Auckland 1145, New Zealand.

D Corresponding author. Email: j.russell@auckland.ac.nz

Wildlife Research 35(3) 215-221 https://doi.org/10.1071/WR07032
Submitted: 9 March 2007  Accepted: 25 September 2007   Published: 20 May 2008

Abstract

Rats continue to invade rat-free islands around the world, and it remains difficult to successfully intercept them before they establish populations. Successful biosecurity methods should intercept rats rapidly, before they can establish a population. Current island biosecurity practice employs techniques used for high-density rat eradication, assuming that they will be equally effective on low-density invaders. However, such approaches are often untested. Adult male Norway rats (Rattus norvegicus) were individually released onto forested rat-free islands in New Zealand to test methods of detecting and eliminating a single invader. Only half the rats released were caught within a two-week timeframe, although the mean time to interception was just under 14 days. Permanent island biosecurity surveillance systems performed better than contingency responses. Success rates were higher on islands where complete coverage could be obtained, although surveillance systems using multiple devices eventually detected most invading rats. For some rats a change of methods was necessary. Single invading rats left a rat-free island despite the presence of excessive natural food resources. With surveillance systems comprising an array of tested island biosecurity devices, and where necessary a contingency response using alternative methods, it should be possible to maintain islands as rat-free even when they have a high reinvasion rate.


Acknowledgements

Thanks to Phred Dobbins, Dane Springmeyer, Melanie Harsch, Alex Hoffmeier, Lucas Morgan and Sarah Hagopian for rat monitoring on Ulva. Thanks to Jo Peace and Jane Dudley for rat monitoring on the Noises. Thanks to the Department of Conservation rodent dog team members Fin Buchanan and Natasha Coad (Jak, Tama and Macy) who provided their services free of charge. We are grateful to the Neureuter family trust for permission to work on The Noises, and Ngati Manuhiri and Department of Conservation Warkworth for permission to work on Hawere. Thanks also to the Department of Conservation Auckland Area Office boat crew for field transport, and the Leigh Marine Laboratory for access to boating equipment. Thanks to John McCallum for permission to trap rats on Pakihi Island and the Karamuramu (Quarry) Island workers for regular transport to Pakihi. Paul Keeling (‘Ditch’) helped advise on methods of detecting and trapping small mammals. This research was funded by the Department of Conservation and performed with University of Auckland animal ethics approval and Department of Conservation high-impact research approval. Financial support was provided to JCR by the New Zealand Department of Conservation, a Top Achiever Doctoral Scholarship, University of Auckland Doctoral Scholarship and Edward and Isabel Kidson Scholarship. Amanda Todd, Mike Thorsen, Charlie Daugherty and three anonymous referees provided useful comments on earlier versions of the manuscript.


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