Habitat preferences of ship rats (2023)

Habitat preferences of Rattus rattus (ship rats) across composite urban landscapes

Predator Free Wellington is pioneering a world-first multispecies eradication in an urban environment, something which has previously only been achieved on offshore islands and fenced sanctuaries. As global commensal species, there’s is no shortage of research out there about the behaviour of Ship rats in densely urban city centres, but like many New Zealand cities, what makes Wellington so special is the combination of manmade and natural zones that make up our capital city. We know from the mahi on Miramar Peninsula over the last couple of years that Ship rats are more abundant in certain habitats, but their specific ecological preferences across varied peopled landscapes is largely unknown.

This research sought to address this knowledge gap by:

1. Understanding ship rat preferences across six different habitat types in the case study area of Oruaiti, part of the Phase 1 project area. The six habitat types included in the research were Developed Urban, Coastal Scrub, Mid-regeneration Native, Capy Ivy, Mixed Vegetation, and Exotic Pine.
2. Using these insights to help inform habitat-based elimination techniques.

Key findings from the research were that:

• Ship rats were detected across all of the assessed habitat types, but presence varied significantly depending on the type of habitat.
• Ship rats were most commonly detected in the Coastal Scrub habitat type, followed by Cape Ivy, i.e. these habitats presented the most favourable conditions.
• There was a moderate abundance of rats in the Mid-Regeneration native habitat, followed by the Mixed Vegetation habitat.
• Developed Urban and Exotic Pine habitats proported an equally low presence of rats.

Based on an assessment of the commonalities between habitats with similar levels of rat presence, it was concluded that:

• Dense vegetative harbourage is the factor most conducive to a favourable habitat, with the availability of habitat-specific food sources and low proximity to human disturbance also of significant influence.
• Natural habitats were considerably more favourable compared to the anthropogenic (manmade) habitats assessed, however, this is applicable to urban areas of high socioeconomic wealth represented in this study.
• It was not possible to form a conclusion about the relevance of native versus non-native vegetation, based on this study.

The recommendation for elimination projects operating in composite urban envrironments is for operational technicians to conduct a habitat assessment prior to then installing a habitat-based grid of devices, whereby network density increases according to favourable habitat conditions.

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This research was conducted in 2023 by Eleanor Dewar, a postgraduate student researcher of Te Pūkenga Open Polytechnic, in collaboration with Predator Free Wellington Ltd.