A range of vertebrate species (birds and mammals) were introduced into New Zealand for food, sport, biocontrol, or aesthetic reasons. Those species that established, have to varying extents, increased in abundance to the stage where they now have negative impacts on agricultural production, conservation, infrastructure, or animal and human health, as well as just being a nuisance in some environments. Because these species have negative impacts on values we care about, they are often termed pests. This term however, is a value judgment and is often site specific. For example, a cat can be someone’s pet at home and therefore valued positively, while being someone else’s pest and valued quite differently when found predating native birds in an adjacent reserve. This dichotomy of values also applies to many of the harvested or hunted species (e.g. possums, deer, chamois, pigs, and tahr). Irrespective of the name we use or the value we attribute to the species, the animal is still the same, and therefore we need to think carefully about our actions if we treat animals differently because of their classification or value. Additionally, we should not justify any inhumane treatment of animals (especially predators) on the basis that those animals cause pain and suffering to their prey. In philosophy, someone using such a justification is considered to have raised the “is-ought problem” (i.e. what is, does not justify what we ought to do).
It is accepted by animal welfare scientists and physiologists that if an animal has a nervous system that is sufficiently developed to relay stimuli from sensors around the body to the brain, and the brain is sophisticated enough to transform those signals into perceived sensations, then the animal is sentient and therefore has the capacity to suffer. New Zealand’s Animal Welfare Act 1999 defines all vertebrates (mammals, birds, reptiles, amphibians, and fish), and any octopus, squid, crab, lobster, or crayfish (including freshwater crayfish) as animals under the Act, therefore accepting that they have the capacity to suffer. It also includes mammals, birds and reptiles in the last half of gestation or development before birth or hatching, and marsupial pouch young.
All the vertebrate species that are controlled in New Zealand as pests are sentient species, and have the capacity to suffer as a result of the wide range of control tools used to reduce their numbers. Accepting that there is a welfare cost (i.e. animals suffer) resulting from our pest management actions, it is incumbent upon all those involved in controlling vertebrate pests to minimize the welfare cost (harm) and maximize the benefits (i.e. achieve the pest management objectives). Not to do so will result in pest management programmes that are not ethical and that could and should be challenged by those concerned about how animals are treated.
To ensure vertebrate pest management programmes are ethical and address animal welfare concerns, managers need to satisfy the following criteria:
Criteria 1-5 relate to the ethical status of a control programme and are often overlooked, while criteria 6 and 7 relate specifically to animal welfare and receive the most attention.
Unfortunately not all pest control programmes satisfy criteria 1-5, especially criterion 3. In this case, rather than not act to minimize the impact of a pest, it is important that managers acknowledge this lack of information and inherent uncertainty associated with it, and make the programme ethical by ensuring adequate monitoring is set up to learn from the operation so future operations will have the necessary information.
When choosing which control tool(s) to use on the basis of minimising the welfare cost, managers have both practical and funding constraints that they have to operate within. That is, the control method with the least welfare cost (e.g. an effective kill trap) might not be a viable option because of practical limitations (i.e. difficult to run kill traps over 50,000ha) or funding limitations (i.e. the budget to control 50,000ha with aerial 1080 bait might be $1.5mill, but to use kill traps might be $4mill). So, to satisfy criterion 6 managers should select the most welfare friendly option within the operational constraints of the control programme. However, constraints, especially funding, should not always dictate method selection if a more welfare friendly method is available at little extra cost. This funding issue raises the question – what willingness is there to pay for improved welfare?
The welfare outcome when a control tool is used, is not solely dependent on the tool per se, but is also a result of how the tool is used. That is, an effective kill trap, if set incorrectly, can result in a poor welfare outcome for a captured animal. Consequently, pest control operators using poisons, traps, or shooting should follow accepted good practice and become familiar with how best to use a tool to minimize welfare costs. As stated in the first paragraph, just because the animals being controlled are considered “pests” does not provide the license to use any method to kill them. For most pest species there are accepted control tools and accepted practices for applying those tools. If an operator uses unacceptable practices then they will be at risk of committing an offence under the Animal Welfare Act 1999.
The relative welfare costs of the vertebrate toxic agents (VTAs) registered for use in New Zealand have been assessed and provide a useful guide for selection based on their welfare impacts. Label conditions are intended to manage animal welfare risks, as well as other risks the user must be aware of. For each of the VTAs the welfare cost can be minimised further by following good practice, and if appropriate include prefeeding to minimize sub-lethal dosing, removing weathered/aged baits to minimise sub-lethal poisoning and bait shyness, and ensuring appropriate presentation (e.g. bait stations) to ensure adequate consumption by the target species and to minimise access to baits by non-target species. All baits should meet required specifications for palatability, hardness, toxic loading, etc.
For leghold traps, the larger more injurious models have been prohibited, but even the smaller ones can cause significant injuries if not used appropriately (see BioNet trap guidelines). It is important that the legislative requirement for trap checking is adhered to (NB, it is a criminal offence under the Animal Welfare Amendment Act (No 2) 2015, not to remove a trapped animal within 12 hours of sunrise the following day the trap was set, and an infringement offence not to have checked traps). All captured animals must be euthanased as quickly and effectively as possible. Trap sites (sets) should be free of vines that can entangle the chain, and possums caught in raised sets should be able to rest on the ground after capture. Traps need to be maintained to minimize the number of escapes.
For kill traps that have a baited trigger, the most important factor is to ensure the bait size and its alignment is such that the animal is struck in the target location that leads to rapid irreversible unconsciousness and death. Some trap models have been tested using the National Animal Welfare Advisory Committee guidelines and the traps that have passed this test should be chosen in preference for those that have either not been tested or have failed.
Cage and box traps generally cause few, if any injuries, but they must be checked daily and if being used in hot weather located in shade so captured animals don’t become hyperthermic.
For shooting, shots should not be taken unless there is a high chance of accurate bullet placement, and that placement is in an area of the body that will result in a rapid death. Calibre choice should be appropriate for the target species.
Content for this page provided courtesy of Bruce Warburton, Science Team Leader, Wildlife Ecology & Management, Landcare Research.