New Zealand Journal of Ecology (1994) 18(1): 19- 28

Ecology of Ship Rats (Rattus rattus) in a Kauri (Agathis australis) Forest in Northland, New Zealand

Research Article
John E. Dowding 1
Elaine C. Murphy 2
  1. P.O. Box 36-559, Northcote, Auckland 9, New Zealand
  2. Department of Conservation, Private Bag 68 908, Newton, Auckland, New Zealand

Home range dimensions and habitat use by ship rats (Rattus rattus) at Puketi, a kauri (Agathis australis) forest in Northland, were examined by live capture and radio-tracking over five weeks in September and October 1993. Home ranges of six females and five males averaged 0.86 ha in area and 174 m in length, with no significant difference in range area or length between males and females. There was substantial overlap in ranges between and within sexes. One adult male increased the size of his range more than four-fold in seven nights in late October, coinciding with the beginning of the breeding season. Some rats changed daytime den sites frequently and others used the same den for a number of consecutive days; rats were found sharing dens on many occasions. Most rats returned to previously-used dens after denning elsewhere. At night, rats spent most of their time active on or close to the ground. There are a number of important differences between our findings and those from other studies of ship rats in New Zealand; we suggest that the different times of year at which the studies were carried out are responsible for some of these differences. Our results, with those of others, suggest that in winter rats of both sexes have 0.5-1.0 ha ranges, but that during the breeding season ranges of males increase while those of females stay similar in size. Trapping indices showed that ship rats were not evenly distributed in Puketi Forest. In December 1993, an aerial poison operation to control brushtail possums (Trichosurus vulpecula) was carried out over the study area, at which time five rats (three male, two female) still carried functioning radio-transmitters. The three males died within four hours on the night following the operation but the two females were alive three days later.