Possum Control Techniques

Possum control techniques and information:

Several different methods for controlling the brush-tail possum currently used within New Zealand. They vary in effectiveness and can pose a threat to humans, animals and wildlife in general. Detailed information on available poisons and traps, with their advantages and disadvantages, are outlined below.

Control methods:

1) Shooting:

Quick, effective and humane.
Effective in smaller open areas such as orchards and areas of pasture.
Uneconomic for larger areas as the sole method of control due to high labour costs.
Only an option in rural areas of the peninsula.
Possums become ‘gun-shy’ and will hide away from shooters.
Licensed, responsible shooters required. Public may have concerns with the use of firearms.

2) Trapping:

The best method for urban areas where poisoning and shooting are not appropriate (domestic animals etc).
May be effective when bait aversion has built up within possum populations.
Kill traps and cage traps relatively humane, but leg-hold traps less so.
The use of some trap types is restricted by city and regional councils in urban areas. Dunedin City Council has a by-law that bans the use of gin traps, but leg-hold traps are approved.
Higher maintenance and labour than using poisons, but less than shooting.

3) Poisons:

Generally considered to be the cheapest and most effective method of control.
Certain poisons have a high degree of health risks associated with their use and can also pose a risk to stock, pets and birds through primary and secondary poisoning.
Poisons vary in their effectiveness, bioaccumulation (build-up in various organisms) and length of time to kill the target species.
Public perception and concerns with certain poisons can be an issue.

Please note: For various reasons the use of sodium fluoroacetate (1080) will not be considered as part of a control regime for the Otago Peninsula.

LINKS:
National Animal Welfare Advisory Committee (NAWAC): for assessing the welfare performance of restraining and kill traps can be found here: http://www.mpi.govt.nz/protection-and-response/animal-welfare/traps-and-devices/

Landcare research trap test results from NAWAC standards can be found here (updated August 2013): http://www.landcareresearch.co.nz/science/plants-animals-fungi/animals/vertebrate-pests/traps

Comparisons of different trap types.

Note: Not all trap types available for possums are mentioned here. Also used, although now less commonly, are BMI 160 (Conibear type traps USA) and LDL 101 (Canada) traps. Both these traps have passed NPCA tests (2005) as per NAWAC guidelines. This summary is not intended as a recommendation of trap types to be used.

1) Kill traps:

Trap type: “Timms”.

Timms trap

Timms trap

Advantages:

  • Instant kill (unlike leg holds)

  • Good around gardens and houses

  • Yellow attracts possums

  • Highly unlikely to trap other domestic animals if appropriate bait used (i.e. fruit)

Disadvantages:

  • Bulky/heavy (1.25kg)

  • Less effective than leg-hold traps (i.e. Victor #1)

  • Not appropriate for large areas

  • Fails independent tests if not baited appropriately.
  • Version 3 trap known to be an improvement.

Trap type: “Warrior/Bulldog”.

Warrior/Bulldog Trap

Warrior/Bulldog Trap

Advantages:

  • Compact

  • Instant kill (unlike leg holds)

  • Ground or tree set

  • Unlikely to capture domestic animals if used correctly

  • Good for large areas

  • Passes independent tests for kill time and escapes

Disadvantages:

  • Heavy (0.890kg)

  • Fewer traps can be carried than leg holds

  • Less effective than leg- hold traps (i.e. Victor #1)

Trap type: “Sentinal”. (Developed from LD 101)

Sentinal trap

Sentinal trap

Advantages:

  • Lightweight (0.550kg)

  • Instant kill (unlike leg holds)

  • Designed for remote areas

  • Ground or tree set

  • No setting handle required

  • Can also be used as bait station

  • Passes independent tests for kill time and escapes

  • Shown to be almost as effective as leg hold traps (Landcare Research)

Disadvantages:

  • Bulky; fewer traps can be carried than leg holds

Trap type: “Possum master”.

Possum master

Possum master

Advantages:

  • Lightweight (0.5kg)

  • Tree and ground set

  • No setting tools required

  • Passes independent tests

Disadvantages:

  • Poor performance in tests for both possums and ferrets

  • Recommended to be tree set vertically to be effective when targeting  possums
  • Less effective than leg- hold traps (i.e. Victor #1)

2) Cage traps:

Trap type: Cage trap.

Collapsible Holden trap

Collapsible Holden trap

Advantages:

  • Appropriate for urban areas

  • Non-target animals caught can be easily released unharmed e.g.

Disadvantages:

  • Bulky and heavy.

  • High labour costs (animals must be killed promptly after capture and trap reset).

  • Only appropriate in urban areas or where non-target species are present.
  • The Animal Protection A ct requires that cage traps are checked every 24 hours by law

3) Leg hold traps:

Note: Leg-hold traps have been used in New Zealand for many years. These traps are used to control pest animals, such as possums, ferrets, stoats and feral cats to protect our native plants and animals, and (in the case of possums) to control bovine tuberculosis. The traps have metal jaws and are designed to catch and hold an animal by a limb, including the foot. Concerns have been raised, both internationally and within New Zealand,  over the humaneness of leg hold traps. The animal welfare concerns are injury and distress associated with being trapped, potential for escape of injured animals, and animals suffering if they are held in the trap too long. Leg-hold traps are less discriminant in capturing target species, and have been known to catch birds and pets.

All leg-hold traps must be set above ground on a tree or post at approx 70cm when there is a likelihood of ground dwelling birds being caught.

The Government has recently decided to restrict the sale and use of leg-hold traps in New Zealand.

From 1 January 2008: No leg-hold traps can be used within 150 metres of a dwelling without the express permission of the occupier or in any area where there is a probable risk of catching a pet animal.

From 1 January 2009: no long-spring leg-hold traps of size 1 ½ or larger and no double-coil leg-hold traps larger than size 1 ½ can be used.

Source: http://www.mpi.govt.nz/protection-and-response/animal-welfare/traps-and-devices/

Trap type: “Victor No1” An example of a typical leg-hold trap currently allowed.

Victor No1 Leg Trap

Victor No1 Leg Trap

Advantages:

  • Light and small.

  • Easy to place and set in remote areas.

  • More effective that other trap types in catching possums

  • Fast reset compared to kill traps (1min vs over 2 min).

Disadvantages:

  • Can be viewed as inhumane causing undue suffering to animals (see above).

  • High risk of injury to domestic animals if used in urban areas.

  • Risk of injury to other non-target and native species.

  • The Animal Protection Act requires live traps be checked every 25 hours by law.

Note: Padded leg-hold traps are now commonly used as a way to reduce injury to non-target species and reduce suffering of target species. Padded leg-hold traps, however, can lead to unacceptable escape rates and can still injure non-target species unnecessarily.

Poisons:

The five poison types most commonly used for possum control in New Zealand by the public are: brodifacoum, pinedone, cyanide paste baits, encapsulated cyanide and cholecalciferol.
1080, or sodium monfluoroacetate, (as previously mentioned) is a controlled substance and is not being considered for use on the Otago peninsula. The main methods of deploying baits and poisons are:
1) Bait stations must be elevated on trees or posts away from ground animals by law to avoid primary and secondary poisoning of non-target species. Stations are filled with cereal based and/or wax coated pellets. Dogs are particularly sensitive to these two anticoagulants – requiring only a 200gm dose to be lethal. Stations provide protection from rain and moisture. The two most common types are the Philproof and the Kilmore which hold up to 2kg of bait. Smaller stations are also available.
2) Bait bags must be stapled to a tree, post or similar. They provide a cheap, weatherproof method of elevating bait away from ground animals. Bags are stapled approx 25cm up a tree and typically a “blaze” of flour and icing sugar is smeared on the trunk above the bag to act as an attractant.
3) Paste form cyanide can be legally applied directly at ground level. Paste is usually applied on a stone, piece of wood or in a station near known possum trails after “pre-feeding”. Paste should be removed or overturned after 2 nights to reduce gas emissions during break-down which can encourage shyness. Removal also reduces chance of harm to non-target species.Note: Cyanide is the only poison legally allowed to be applied at ground level.

Brodifacoum:

(First generation anticoagulants)

Trade names: Talon ®, Pestoff ®, Pinedone ® .

Brodifacoum/Pindone Toxin

Brodifacoum/Pindone Toxin

(bait station filled with brodifacoum)

Characteristics

Advantages

Disadvantages

Anticoagulants act by interfering with the normal  clotting agents in the liver of vertebrates. This results in an increase in blood-clotting time until the point where no clotting occurs which leads to death.

Dogs are particularly sensitive to first generation anticoagulants. In the instance of poisoning a vet can administer vitamin K as an effective antidote.

  • No license required

  • Less toxic to invertebrates than mammals and birds

  • Effective against possums that havedeveloped poison/bait shyness

Pinedone:

Residues in sublethally poisoned animals (particularly liver) are less persistent than brodifacoum

  • High risk of secondary poisoning of non-target species

  • 2-4 weeks for possums to die

  • Expensive costs when possum densities are high

Brodifacoum:

Very environmentally persistent.

Present > 1 year in liver of vertebrates.

Can put meat for human consumption at risk.

Pinedone:

Large amount of bait required to be eaten (1-2kg/possum)

Cyanide (sodium and potassium) paste and encapsulated pellet baits:

Trade names: Feratox ®

Feratox Toxin

Feratox Toxin

(Feratox ® tablets or capsules)

Characteristics

Advantages

Disadvantages

Cyanide is a HIGHLY TOXIC “asphyxiant” which causes a rapid decrease in Oxygen supply. Animals are unconscious within seconds and die within minutes. Available in paste and pellet formulations containing 475–600 g/kg cyanide.

Cyanide does not accumulate in soil or food chain and is not mutagenic or carcinogenic.

.

Paste:

  • Cheapest option available

  • Most humane poison, rapid kill (minutes)

  • Low secondary poisoning risk

  • Low environmental persistence

Feratox ®:

  • Safer to handle than paste.

  • Low hazard to non-target species.

Paste:

  • Only available to  licensed contractors

  • bait-shyness” can develop, leads to ineffectiveness

  • Highly toxic and can kill ground birds e.g. kiwi and weka

Feratox ®:

  • Only available to licensed contractors

  • Can persist in environment for 2-3 months

Cholecalciferol:

Trade names: Campaign ®, Feracol ®

Cholecalciferol Toxin

Cholecalciferol Toxin

Characteristics

Advantages

Disadvantages

Feracol is a peanut butter flavoured bait, highly palatable to possums. The active ingedient is Cholecalciferol (vitamin D3) in a concentrated form. This is very toxic to some animals in particular, POSSUMS. Feracol kills by elevating plasma calcium levels resulting in heart failure.
  • No license required

  • Lower risk of primary and secondary poisoning of dogs and birds than other poisons

  • Does not persist in soil or water

  • Residues in sub-lethally poisoned animals do not have prolonged persistence

  • Fate and persistence in the environment not well understood

  • Treatment for accidental poisoning available but complex

  • Most expensive type of bait, however pre-feeding can make it cost effective

Sources: Weblinks and Publications

1. http://www.mpi.govt.nz/protection-and-response/animal-welfare/traps-and-devices/

2. http://www.traps.co.nz

3. http://www.landcareresearch.co.nz/science/plants-animals-fungi/animals/vertebrate-pests/traps

4. http://www.doc.govt.nz/nature/pests-and-threats/animal-pests/animal-pests-a-z/possums/

5. http://www.mpi.govt.nz/protection-and-response/animal-welfare/traps-and-devices/

6. http://www.landcareresearch.co.nz/publications/infosheets/possums/traps.pdf?traps

7. Thomas, Malcolm and Sessions, Laura (NPCA) Private landowners’ guide to possum control; practical tools and techniques for controlling possums on private land. Produced by the National Possum Control Agencies. ISBN 0-9583736-3-9

8. Warburton, Bruce (Landcare Research) 2005. A guideline for using kill traps to trap small mammals. National possum control agencies, Ministry of agriculture and forestry.

Published Papers (PDFs)

Kill-traps-vs-leg-holds

Kill traps vs leg holds (gnd set)

Raised leg holds vs gnd set

Tree set kill traps vs gnd set leg holds DOC

MSDS sheets (poisons)

Brodifacoum (Pestoff) safety sheet

Cholecalciferol (Feracol)-Safety-Data-Sheet

Cyanide paste (Cyanara50)-Safety-Data-Sheet

Cyanide paste (cyanide sodium) saftey sheet

Feratox (cyanide capsules)-Safety-Sheet

Pindone safety sheet