New Zealand Journal of Ecology (1995) 19(1): 19- 27

Population-Dynamics and Diet of Rodents on Rangitoto Island, New Zealand, Including the Effect of a 1080 Poison Operation

Research Article
C. J. Miller 1,2
T. K. Miller 1,2
  1. Centre for Conservation Biology, University of Auckland, Auckland, New Zealand
  2. Present address: C/- Department of Conservation, Private Bag 701, Hokitika, New Zealand

The objective of this study was to quantify the population dynamics, morphological characteristics, and diet of rodents on Rangitoto Island (Hauraki Gulf, New Zealand) to provide information for the future development of an eradication strategy. An aerial 1080 operation to eradicate possums and wallabies was carried out two months after the study began. The effects of this operation on rodent population dynamics are discussed. Both ship rats (Rattus rattus) and mice (Mus musculus) were trapped on Rangitoto Island over a 15 month period. A two month decline in mouse abundance was noticed following poisoning; following this the population recovered rapidly, reaching a Peak of 12 captures per hundred trap nights (12 C100TN(-l)) in autumn and then declining over winter. A longer decline in ship rat abundance was observed, although this reached a pre-poisoning level of 1.6 C100TN(-l) in April. Thereafter the population did not reach pre-poisoning levels again. Total body length and weight were significantly related to age, and were similar to those of mice and ship rats recorded in other New Zealand studies. The majority of breeding appeared to occur between September and May for both species. There was evidence of delayed reproductive maturity for female mice and mts born at the end of summer. A relatively large number of young mice were caught in autumn, with very few being caught in spring. Invertebrates were the major component of both species' diet, with weta (Hemideina thoracica) predominant, while plant matter was a minor constituent. The nematodes Physoloptera getula and Mastophorus muris were present in the stomachs of 22% of mice and 59% of ship rats.