Wild and feral mammal control

Policy type: Policy
Reference: 13a
Status: Under review
Date ratified: August 2016

Policy

The control of pest mammals is a necessary part of conservation work to reduce the destructive impact they have on our environment The NZVA considers that the welfare of pest mammals must be given serious consideration when methods of killing or otherwise controlling them are selected. Lethal methods must result in irreversible loss of consciousness followed by death as quickly as possible with a minimum of negative experiences such as pain, fear and breathlessness. Further research to identify new control methods for pest species that effectively and humanely manage their populations is required.

Explanation

Mammals considered pests in New Zealand include any land mammals living in a wild state if they compete with domestic or native animals for food, if they might transmit diseases to humans or animals, or if they damage or kill crops, pasture or native animals or otherwise threaten biodiversity or if they are considered to be a nuisance. It also includes animals that are deemed as pests by legislation. Presently mammals that may be deemed pests and subject to control include: possums, rats, mice, stoats, ferrets, feral cats, rabbits, pigs, deer, wallabies, goats and horses.

A current list of animals considered pest species is maintained by the Department of Conservation at http://www.doc.govt.nz/nature/pests-and-threats/animal-pests/animal-pests-a-z/ and at the National Pest Control Agencies web site at http://www.npca.org.nz/index.php/vertebrate-pests

Pest mammals are sentient beings capable of experiencing pain and suffering. Veterinarians have an obligation to ensure humane treatment of all animals, whether they are classified as “pests” or not, so methods used for control must be as humane as is practical.

The method chosen for pest control must:

  • have a scientific basis
  • take account of animal welfare
  • be as specific as possible for the species targeted,
  • minimise the risk of inadvertent killing or injury to other species
  • minimise damaging effects on the environment
  • be effective in achieving the aims of the operation to avoid the unnecessary suffering of pest animals

The NZVA also recognises that the relationship between pest mammals, other animals and the environment is complex, requiring that any pest control system should be integrated into total land management programmes that address issues such as overgrazing, erosion, land rehabilitation, prey switching, and preservation of endangered fauna and flora and their natural habitats.

Guidelines

The following guidelines are for veterinarians when advising lay-people on the best methods to use to control pest mammals when either a veterinarian is not available or it is not practical to use a veterinarian.

The NZVA notes that other sources of expertise and practical advice include the National Possum Control Agencies (NPCA), the Department of Conservation (DOC) and the Pest Management Association of New Zealand (PMANZ).

Various methods are available to control pest mammals. These include use of capture traps, kill traps, poisons, shooting, hunting with dogs and biological agents.

1. Traps

Trapping is a commonly used method of pest mammal control. Traps may be intended to kill (kill traps) or capture (such as leg-hold and cage traps).

The NZVA has concerns regarding the use of any type of leg hold trap for pest control as these may cause injury and suffering to target species as well as to non-target species even when best practice principles are followed.

The NZVA does not support their use but acknowledges that in the absence of suitable alternatives with improved welfare outcomes, leg hold traps are a necessary option for pest management in some instances.

To ensure humane pest control by trapping, with minimum stress, the NZVA prefers the use of species-specific kill traps that have passed animal welfare impact testing according to criteria set by the National Animal Welfare Advisory Committee. All traps should be strategically positioned and baited to target pest species.

The National Animal Welfare Advisory Committee (NAWAC) has developed a trap-testing guideline (https://www.mpi.govt.nz/document-vault/8521).

Landcare Research has undertaken testing of kill traps against this guide. The results for cats are available at: http://www.landcareresearch.co.nz/science/plants-animals-fungi/animals/vertebrate-pests/traps/target-species

Live Trapping

Live-capture traps include cage traps and leg-hold traps.

Section 36 (1)(a) of the Animal Welfare Act requires that live-capture traps must be inspected within 12 hours after sunrise on each day the trap remains set.

Section 36 (1)(b) requires that trapped animals be removed or cared for properly or killed without delay.

The Animal Welfare (Leg-hold Traps) Order 2007 restricts the way that leg-hold traps are used and the types of traps that may be used. The Lanes Ace ‘gin’ trap can no longer be sold or used and all leg-hold traps larger than size 1 and a 1/2 may not be sold or used. Leg-hold traps cannot be used within 150 m of a dwelling without permission from the occupier and may not be used where there is a “probable risk” of catching a companion animal.

Only padded-jaw types like the Victor Soft Catch traps are acceptable, as those with hard jaws frequently cause extensive injuries to the trapped animal. Excellent information regarding the welfare performance of various traps is available through the Predator Free NZ web site at http://predatorfreenz.org/welfare-performance-of-animal-traps/

Live capture traps should be placed in the shade during periods of warm weather, and trappers should minimise stress to trapped animals from the approach of humans and dogs.

If animals captured in live-capture traps are to be killed, this must be carried out promptly and humanely.

Euthanasia by a veterinarian may be the most humane option but this is seldom practicable.

Practical methods to kill trapped animals that minimise the suffering of the animal are:

  • A single shot to the head from a .22 cal rimfire rifle.
    • In smaller pest species such as feral cats, the shot should be taken when the animal is motionless with the rifle muzzle 3-5 cm from the head to ensure maximum impact and reduce the likelihood of bullet ricochets. Firearm users must accurately place the shot to ensure a humane kill of the target species.
    • Firearms are also an effective option for euthanasing larger animals. Animals can be shot from a distance, thus lessening the disturbance to the captured animal.
    • Air rifles and pistols do not deliver sufficient muzzle velocities to kill possums or feral cats with a single shot and should not be used.
  • Blunt force trauma to the head (experienced users only when other methods not practical)
    • This involves striking the animal on the head with a hammer, bar or stout wooden stick. While this method can be very effective, it requires the operator to be confident and strong enough to ensure the blow(s) stun the animal immediately and/or kills it. Although some people can kill possums or feral cats by using only one or two strikes, less experienced people often use several strikes, resulting in a protracted period of stunning which is not acceptable. If the animal is likely to move before or as it is struck, restrain it first by holding the tail or using a net or forked stick (National Pest Control Agencies, 2015).
  • Cervical dislocation
    • Mice and small-bodied rats can be killed quickly by cervical dislocation by placing a stick, pencil, or pen across the neck and lifting the tail and body upwards to break the neck (National Pest Control Agencies, 2015).

Possums may be trapped either with a pouch young or a back-rider and it is important that dependant young are also killed humanely. Suggested methods for use in the field are blunt force trauma to the head of the larger back-riders or decapitation of pouch young.

In all cases, death should be confirmed by the operator.

Drowning by immersing cages or animals in water is not acceptable for any species.

The sale and use of glueboard traps for rodents is now completely prohibited under the Animal Welfare (Glueboard Traps) Order 2009.

Releasing trapped animals

Non target animals that have been trapped need to be inspected to ensure they are not injured before they are released. If significant injuries are detected on an animal that is not an endangered species, the animal should be euthanased immediately.

Injured threatened or endangered species should be promptly seen by a veterinarian.

2. Shooting

Operators should be licensed and experienced and use a firearm suitable for the target species. They need to be familiar with the anatomy of the target species and be capable of killing the pest animal with one headshot. If a lactating female is shot, efforts should be made to locate the dependant young and kill them humanely.

3. Poisons

Poisons registered for use in feral mammal control in New Zealand include: 1080, Zinc phosphide, PAPP (paraaminopropionphenone), phosphorus, cholecalciferol, cyanide, and anticoagulant toxins such as Brodifacoum, Bromodialone, Diphacinone, Coumatetralyl, Coumatetralyl+Cholecalciferol, Pindone and Flocoumafen. A controlled substances license is required to use bait formations containing Cyanide, 1080, Phosphorus and some formulations of Pindone.

Poisons (vertebrate toxic agents) may be acceptable if the method chosen is the one that causes the least harm of those available and practicable and a minimum of negative experiences such as pain, fear and breathlessness.

Veterinarians should be aware that all Vertebrate Toxic Agents (VTA’s) cause at least moderate welfare impacts and that some commonly used VTA’s (for example anti-coagulants) have significant welfare impacts associated with their use. Others, such as cyanide and PAPP (4-aminopropiophenone/Para-aminopropiophenone), cause death by hypoxia and have the advantage of lower duration of time from the emergence of clinical signs to loss of consciousness. As such these are considered relatively humane – however, these are not available for use by the public. Fisher et al (2010) (https://www.mpi.govt.nz/document-vault/4009) outlines the relative welfare impacts of all VTAs used for mammals in NZ.

Vets should also be aware that VTA’s may also have impacts through persistence in the environment and secondary poisoning of non target species due to consumption of affected pest carcasses. Methods should be employed that minimise the risk of poisoning to non-target species, with attention given to appropriate bait use and the design and placement of the stations. Cold and dry conditions promote the risks of secondary poisoning due to slower decomposition conditions. Public areas where bait has been laid must be adequately signposted and the community notified of the poisoning campaign.

The NZVA has a Position Statement on use of 1080 for pest control (13b) which states that in the absence of effective alternatives, the continued use of 1080 as a means of pest control (possums and some other introduced species) is necessary to assist the eradication of bovine tuberculosis and the conservation of New Zealand’s unique native flora and fauna.

Inadvertent poisoning of companion animals can be reported to the poison manufacturer or the appropriate authority. Any cats or dogs that owners suspect may have consumed poison or a poisoned carcass must seek immediate veterinary assistance. The National Poisons Centre (0800 76 47 66) can also provide advice on therapy for poisoned animals. If a dog is suspected on eating a contaminated carcass or bait and veterinary assistance is not immediately available, prompt induction of vomiting will reduce the risk of a fatal dose. Methods that can be used to induce vomiting in the field include:

  • 1-2 crystals of washing soda administered orally
  • 1-3 teaspoons of table salt administered orally

Veterinary advice should still be sort at the earliest convenience as emptying of the stomach may not be complete. Do not attempt to induce vomiting in a dog that is seizuring.

4. Hunting with dogs

The NZVA has concerns about using dogs to hunt feral mammals, in particular, the welfare of feral pigs. Pigs can experience severe prolonged welfare impacts if mauled by dogs before they are killed or if they escape, and, there is also a high risk of serious injury to the dogs.

To promote more humane treatment of the animals involved, hunters should be encouraged not to use holding dogs, which physically attack the pigs, but to use only “finder” and “bailer” dogs. Hunters should be encouraged to carry a firearm suitable for killing pigs as well as a knife and to provide their dogs with protective collars. Hunters must take all necessary steps to ensure that their dogs do not inflict unnecessary pain on the pig and dogs should not be allowed to maul or kill pigs.

Hunters should check to see where poisons have been laid and avoid these areas, or use muzzles if hunting with dogs due to the serious risks that these compounds pose to dogs if ingested.

Poorly trained dogs may kill native bird species and DOC encourages hunters to have their dogs undergo avian awareness and aversion training, and ensure they remain under control at all times (Department of Conservation, 2016)

5. Biological agents</4>

This includes the introduction of a disease that targets the pest species along with methods that halt reproduction. In general, the NZVA finds the introduction of a disease intended to cause death less acceptable as a means of pest control and supports methods that are more humane and result in a rapid death. Biological control agents and methods ideally should have minimal effect on the normal behaviour and demeanour of the animal (unless such effects are part of the control objective).

Where agents will cause death of some animals, death should be as rapid and as free from pain, apprehension or disorientation as possible. The level of these undesirable effects should be comparable with, or less than, effects caused by non-biological control agents. Individuals that recover should be minimally affected (Australian Veterinary Association, 2010).

The NZVA recommends that in areas where a solution containing rabbit calicivirus is being intentionally applied for rabbit management, or where the disease is endemic, owners of pet rabbits should be encouraged to vaccinate against the virus.

The NZVA is opposed to the introduction of the myxomatosis virus for the control of pest rabbits because of the degree of suffering it induces prior to death.

6. Fencing

The NZVA applauds the use of excluder fencing to protect vulnerable areas, while acknowledging that the cost of such fencing may prevent it use on a widespread basis.

7. Feral Cats

The management feral cats can be a contentious issue. Feral cats are defined under the Companion Cats Code of Welfare (2007) as cat which is not a stray cat and which has none of its needs provided by humans. While recognising the importance of cats as a companion animal in New Zealand society, the NZVA is aware that this species can pose a considerable risk to wildlife, including endangered native species where cats exist as a feral pest species. Best practice guidance for feral cat control is available from the National Pest Control Agencies at http://www.npca.org.nz/index.php/a-series-best-practice

8. In-burrow rabbit control methods

The in-burrow rabbit control methods currently registered and available for use in New Zealand are chloropicrin and magnesium phosphide (fumigants) and ‘The Rodenator’, a device designed to create an explosion in rabbit burrows through the ignition of flammable gas. Gaps exist in the scientific evaluation of the welfare impacts of these methods on rabbits; however the literature indicates that the use of carbon monoxide as a rabbit burrow fumigant is relatively more humane than either chloropicrin or phosphine-generating fumigant formulations and may be a useful addition to rabbit control tools in the future (Fisher & Campion, 2010)

9. Live capture

Use of this method must account for the risk of injury and stress to the animals during capture, subsequent handling and transport, as euthanasia may be preferable in some circumstances.

References

Animal Welfare Act 1999. (n.d.). Retrieved from http://www.legislation.govt.nz/act/public/1999/0142/latest/DLM49664.html

Beausoleil, N., Fisher, P., Warburton, B., & Mellor, D. (2010). Vertebrate toxic agents and kill traps in mammal species . Unpublished report prepared for Biosecurity New Zealand.

Biosecurity Act 1993. (n.d.). Retrieved from http://www.legislation.govt.nz/act/public/1993/0095/latest/DLM314623.html

Cowan, P., & Brown, S. (2012). A review of best practice management for humane and effective vertebrate pest control, Technical Paper No: 2012/28. Ministry of Primary Industries. Retrieved from https://www.mpi.govt.nz/document-vault/4051

Department of Conservation. (2016). Hunting with Dogs. Retrieved from Department of Conservation: http://www.doc.govt.nz/

Department of Primary Industries, NSW Government. (2014). Vertebrate pest control manual. NSW Department of Primary Industries. Retrieved from http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0019/439201/Vertebrate-pest-control-manual-2014.pdf

Fisher, P. (n.d.). Possums...the pros and cons of different poisons. Landcare Research.

Fisher, P., & Campion, M. (2010). In-burrow rabbit control methods. Landcare Research. MAF Biosecurity New Zealand. Retrieved from https://www.mpi.govt.nz/document-vault/4009

Landcare Research. (2010). How humane are our pest control tools? : Technical paper no: 2011/01. MAFBNZ Operational Research. Retrieved from https://www.mpi.govt.nz/document-vault/4009

National Pest Control Agencies. (2015). A11: Feral and stray cats, monitoring and control, A preliminary guideline towards good practice. Wellington: National Pest Control Agencies. Retrieved from http://www.npca.org.nz/images/stories/NPCA/PDF/a11_feral%20and%20cats_2015-nov_lr_opt.pdf

National Pest Control Agencies. (2015). Leghold traps, A guideline for capturing possums, ferrets and feral cats using leghold traps. Wellington: National Pest Control Agencies. Retrieved from http://www.npca.org.nz/images/stories/NPCA/PDF/a4.1_leghold%20traps_2015-nov_lr_opt.pdf

Wild Animal Control Act 1977. (n.d.). Retrieved from http://www.legislation.govt.nz/act/public/1977/0111/latest/DLM16623.html

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