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RESEARCH ARTICLE
Contents Vol 33(7)

Population ecology of Norway rats (Rattus norvegicus) and interference competition with Pacific rats (R. exulans) on Raoul Island, New Zealand

Grant Harper A C and Dick Veitch A B
+ Author Affiliations
- Author Affiliations

A Department of Conservation, Private Bag 68908, Newton, Auckland, New Zealand.

B Present address: 48 Manse Road, Papakura, New Zealand.

C Corresponding author. Present address: Department of Conservation, PO Box 743, Invercargill, New Zealand. Email: gharper@doc.govt.nz

Wildlife Research 33(7) 539-548 https://doi.org/10.1071/WR05096
Submitted: 26 October 2005  Accepted: 14 August 2006   Published: 15 November 2006

Abstract

Norway rats (Rattus norvegicus) are sympatric with, and more often trapped, than the smaller Pacific rat (R. exulans) on Raoul Island, New Zealand. Rats were removed from a four-hectare grid by trapping and poisoning in the winters of 1994, 1995 and 1996. Pacific rats were trapped in increasing numbers only after Norway rats were removed. Norway rats also ate significantly more bait than Pacific rats. Competitive interference of Pacific rats by Norway rats was apparent, which casts doubt on the ability to accurately monitor individual species abundance within assemblages of rat species and to effectively manage them in control grids. Snap-trapping lines provided baseline data on the abundance of the two species before, during and after the removal grids were operated. Maximum abundances of rats were recorded in late summer and autumn following spring and summer breeding.


Acknowledgments

We thank the Department of Conservation for providing the opportunity for the research to be carried out. Nick Torr, Fiona Kemp, Christine Visser, Kirsten Mackay, and Herm Binnie helped set up and run the grids. Ian McFadden, Elaine Murphy and Harald Steen gave technical advice. Henrik Moller, Wendy Ruscoe and two anonymous referees provided comments on the draft manuscript. The use of rat traps and poison bait stations was approved by the New Zealand Department of Conservation Animal Ethics Committee.


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