8 Boffa Miskell Ltd | Pest Animal Management Plan | Wharekirauponga Compensation Package | 30 May 2022 2.3 Possums Possums were first introduced to New Zealand from Australia for the fur trade in 1837, followed by a second successful release 20 years later. Preferred habitats are forests, especially podocarp-broadleaf forest (Department of Conservation, 2019). Home ranges of females are between 0.6 and 2.7 ha, while that of males are between 0.7 and 3.4 ha (Department of Conservation, 2019). In New Zealand, possums are both a predator of native wildlife and a heavy browser of many species of native trees. Although possums are mainly herbivorous and feed on flowers, fruit, and leaves, they will also opportunistically eat eggs, chicks, and invertebrates. Predation by possums on the eggs and nestlings of native bird species such as kōkako, kiwi, and kereru is widespread throughout New Zealand (James & Clout, 1996). Populations of invertebrates such as native snails and weta may also be severely depleted, particularly when alternative food sources are scarce. Possums also disrupt ecological processes such as flowering, fruiting, seed dispersal and germination. In addition, they also serve as vectors of bovine tuberculosis (TB). Possums will be controlled across the WAPMA, primarily via trapping and toxic baiting. Possums are not particularly susceptible to first-generation anticoagulant baits that are often used for rat control (e.g. diphacinone). They can consume large quantities of these baits before consuming a lethal dose, which in turn can reduce the efficacy of rat control. For this reason, an initial population knockdown of both possums and rats be should via an aerial 1080 operation (as proposed in Section 5.0), possum numbers can be maintained at low densities primarily via trapping with a focus on preventing reinvasion. 2.4 Mustelids Three species of mustelids are present in New Zealand; stoats (Mustela erminea), ferrets (M. furo) and weasels (M. nivalis vulgaris). Stoats and ferrets are able to be controlled via trapping and use of some primary and secondary poisons, but there are currently few adequate control options for weasels (although some may be caught with the tools used for targeting rats and other mustelids). Each species has its own unique set of behavioural and morphological characteristics: • Stoats possess the typical ecological characteristics observed in many opportunistic species, such as their small body size, short life span and rapid reproductive cycle (Lough, 2006). Populations are typically unstable through both time and space, as their density and distribution are predominantly controlled by prey availability (King & Powell, 2007; Lough, 2006). Home range sizes vary significantly depending on a range of variables including sex, season, and food availability. In a study on the Otago Peninsula, the average home range size was 83 ha for female stoats and 133 ha for male stoats (Moller & Alterio, 1999). Stoats can cover long distances, and dispersing juveniles may come from over 20 km away (King & McMillan, 1982). Stoats can exhibit significant neophobia or weariness of new objects in their environment, which must be factored into control strategies. • Ferrets are wide ranging with average home range estimates of 18–265 ha for females and 19–760 ha for males, although home ranges are smaller during the breeding season between August and February (Gillies, 2007). Juvenile ferrets may only move small distances (some have been recorded having home range lengths of only 100 m). Ferrets are typically wary of novel objects, which can pose an ongoing challenge to their control. This can be addressed by placing traps that are maintained to a high standard
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