Suchergebnisse

The behaviour, movements and fate of radio-tagged brushtail possums
(Trichosurus vulpecula) were studied after they were
translocated between sites on farmland in two areas in the southern North
Island, New Zealand. At both sites some possums remained near the release site
while others moved up to 12.5 km before settling. At one site, four possums
returned distances of about 3.9 km from the release site to their sites of
capture (homing), with two of these homing successfully twice. Translocated
possums displayed some of the characteristics of naturally dispersing possums
but, unlike them, their long-distance movements were not male-biased nor made
particularly by juveniles. The location and availability of suitable nest
sites appeared to influence the movements of translocated possums, but no
other major influences of landscape features on their patterns of movement
were detected. Survival during the first 9 weeks after translocation was not
influenced by sex, age, weight, distance moved or time since release.
Translocated possums on New Zealand farmland, where the main predators are
people and vehicles, suffered much lower mortality than possums in a similar
study in Australia, where canids, particularly foxes, were a major cause of
death.

The suitability of the nematode Parastrongyloides trichosuri (Nematoda: Strongyloididae) as a genetically modified vector for transmissible fertility control of introduced brushtail possums (Trichosurus vulpecula) is being explored in New Zealand. This review of progress in assessing the ecological and epidemiological characteristics of P. trichosuri against a set of essential properties for a suitable transmissible vector indicates that the parasite appears to have all the attributes of a highly effective vector, although additional information on persistence at low host density and on the outcome of competition between existing infection and new (recombinant) strains is needed to confirm this. Concerns have been raised about risks to possums and other marsupials in Australia from a genetically modified form of P. trichosuri. An international body with responsibility for managing consultation and debate about issues arising from the proposed use of genetically modified organisms for vertebrate pest management has been suggested as a way of addressing such concerns. A key issue remains as to which agency or group of agencies would take responsibility for such a body. A joint meeting of relevant agencies and researchers is needed urgently to begin the process of moving this issue forward.

Long-distance movements of juvenile brushtail possums
(Trichosurus vulpecula) from three habitats on farmland
in Hawke's Bay, New Zealand, were studied by radio-tracking after a
poisoning operation. In the five years after the possum population on the
study site had been reduced by 90%, the population recovered to about
half its initial density. During that time, about 25% of radio-tagged
juveniles dispersed 2 km or more, a maximum of 12·8 km from their natal
area, with no significantly preferred direction. A greater proportion of males
dispersed than females. All but one of the juveniles dispersing did so before
they were one year old, and most made several moves before settling. The
bimodal timing of dispersal in summer and late winter–early spring
reflected an underlying similar pattern of breeding. A higher proportion of
possums dispersed from the low-density pastoral and cropping habitat than from
the higher-density habitats of swamp and willows. The dispersal behaviour of
juveniles after the control operation differed little from that before,
suggesting that dispersal of possums is not strongly influenced by
density-dependent factors at the natal site.

Context
Control of unwanted wildlife ('pest' animals) is undertaken for conservation and economic reasons, and when such animals are considered a nuisance. Such control should be undertaken using approaches that minimise, as far as possible, detrimental impacts on the welfare of the animals. Using a scientific framework based on the Five Domains model, the relative welfare impacts of pest control methods can be compared across methods and pest species.

Aims
We demonstrate the application of a modified version of this framework to evaluate the relative impacts of seven Vertebrate Toxic Agents (VTAs) used to control brushtail possums (Trichosurus vulpecula) in New Zealand. The evaluation is used to produce a ranking of the seven VTAs based on their relative impacts on possum welfare.

Methods
Scientific literature describing mode of toxic action, specific effects in possums or other animals and reports from human poisonings was collated as reference material for a panel of six experts. The panel produced a median welfare impact score ('none' to 'extreme') for each of the Five Domains. The 'Overall Grade' (1 to 8) reflected the intensity and duration of all impacts of a VTA on possums.

Key results
All VTAs evaluated have at least moderate impacts on possum welfare, lasting for at least minutes. Cyanide was assessed as having the lowest welfare impacts (median grade 4), and cholecalciferol and the anticoagulants the highest impacts (7.5 to 8). Zinc phosphide was assigned an intermediate grade (6) with high confidence. While the overall impacts of sodium fluoroacetate (1080) and phosphorus were also assessed as intermediate (6), the panel's confidence in these scores was low.

Conclusions
From an animal welfare perspective, anticoagulant poisons and cholecalciferol should be the least preferred options for controlling possums in New Zealand, as VTAs with less severe welfare impacts are available.

Implications
The results of such assessments allow animal welfare impacts to be integrated with other factors in wildlife management decision-making and policy development, and are thus useful for managers, researchers, regulators and operators. Evaluation of welfare impacts aligns with the goals and mandates of ethical wildlife control and may also be valuable in wider wildlife research and management activities.