<I>Rattus rattus</I>

Artificial nests and tracking tunnels are alternative predator encounter devices that can be used to predict predation risk to native species. Tracking tunnels are used ubiquitously in New Zealand, whereas artificial nests are used extensively overseas. To assess whether these devices give similar information about predation risk, we compared tracking tunnel and artificial nest data from 16 native forest fragments in the central North Island over two summers.

Multiple paternity within litters has been recorded among a variety of small mammal species, including some species of rodents. Although multiple mating has been observed in wild Rattus populations, whether such mating results in litters with multiple paternities has not been established previously. For studies involving invasive species, awareness is useful of the level of genetic diversity a single pregnant invader can bring to a population.

Ship rat (Rattus rattus) density was assessed by snap-trapping during summer and autumn in eight indigenous forest fragments (mean 5 ha) in rural landscapes of Waikato, a lowland pastoral farming district of the North Island, New Zealand. Four of the eight were fenced and four grazed. In each set of four, half were connected with hedgerows, gullies or some other vegetative corridor to nearby forest and half were completely isolated.

The diet of 871 stoats (Mustela erminea) caught within the Okarito Kiwi Sanctuary, South Westland, New Zealand, between 2001 and 2004 was studied by assessment of gut contents. Stoat and ship rat (Rattus rattus) captures were used as a measure of relative abundance over time, and rat and mouse (Mus musculus) abundance was indexed using tracking tunnels between spring 2002 and winter 2004. There were major increases in rat captures in spring of 2002 and again in spring of 2003. Stoat captures peaked in the following summers, as rat captures declined.

Control of one pest species may permit increases in abundance of other pests, thereby reducing the overall net benefit from pest control. We provide evidence that control of introduced possums (Trichosurus vulpecula) may increase ship rat (Rattus rattus) abundance in some New Zealand native forests. Ship rat abundance in a podocarp–hardwood forest was assessed using simple interference indices over 14 years (1990–2004) that included two aerial possum-poisoning operations (1994, 2000).

We developed a capture-mark-recapture protocol for measuring the population density (D) of ship rats (Rattus rattus) in forest. Either mesh cage traps or Elliott box traps were set at each of six sites (48 traps per site for 5 nights) in the Orongorongo Valley on two occasions in autumn 2003. Cage traps only were set at three sites in autumn 2004. Rats were caught much more readily in cage traps than in Elliott traps and none were recaptured in Elliott traps. Additional food, bedding and trap covers reduced mortality and interference with traps.