Boffa Miskell Ltd | Pest Animal Management Plan | Wharekirauponga Compensation Package | 30 May 2022 7 2.0 Target pest animal species 2.1 Rats Three rat species invaded New Zealand, with the Norway rats (Rattus norvegicus) and ship rats (R. rattus) being the most common on the mainland. Rats are generalist omnivores; their diet includes seed predation and preying on small animals such as invertebrates, reptiles, amphibians, and juvenile birds. They compete with native birds for nests and burrows, and have been implicated in the decline of a number of threatened birds, particularly seabirds (Auckland Council, 2019). Although rats are not as wide-ranging as mustelids, they are capable of invading areas quickly over small distances and have a high reproductive rate. Norway rats are the largest of the rat species. As ground-dwellers, they pose significant threats to ground-nesting birds (Amori & Clout, 2002; Bellingham et al., 2010). Norway rats are the most capable swimmers of the rat species in New Zealand, are able to swim up to two kilometres across open water (Russell et al., 2008), and are frequently found around wetlands and waterways. This species is distinguishable from ship rats by small ears that are unable to fold down over their eyes and a tail that is shorter than their body length. Ship rats are very agile and are frequent climbers, preferring to nest in trees and shrubs rather than on the ground. They can be distinguished from Norway rats by their tail which is longer than their body length and large ears that can fold down over their eyes. Ship rats are considered the most significant predator of Leiopelma species with multiple predation events recorded over the years (Egeter et al., 2015). Although there are no direct records of ship rat predation on Leiopelma species at Wharekirauponga specifically, they are common in this area and are likely having a negative impact on the Archey’s and Hochstetter’s frog populations here. Rats will be controlled across the Wharekirauponga animal pest management area via intensive trapping and toxic baiting. 2.2 Mice The impacts of mice on native biodiversity (flora and fauna) as either predators or competitors is not yet well understood. There is some evidence to suggest mice are predators on native lizards, frogs, and invertebrates (Egeter et al., 2015; Norbury et al., 2014; Wedding, 2007), and mouse populations may increase when larger predators (particularly rats, mustelids, and feral cats) are removed from an area resulting in additional impacts on frogs (Germano et al., in press). Unfortunately, there is no effective large-scale mouse control tool (either trap, toxic bait or otherwise) currently available. Mouse control in this WAPMP will therefore be undertaken alongside rat control (using a combination of traps and baits), and their populations will be monitored via chew cards (with detections also possible on camera traps and novel real-time monitoring tools, if deployed in the future).
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