Rodents

The rats in New Zealand are introduced pests and threaten the long-term survival of native species.

1200px WildRat5There are two introduced European rat species in New Zealand, the Norwegian rat (Rattus novegicus) and the ship rat (Rattus rattus).

Rats are a threat to breeding birds as they prey on eggs and chicks. Ship rats are a particular problem as they are exceptional tree climbers. Our native birds have not evolved with rats and have no defences against them. Many native bird species also breed very slowly and can’t keep up with the present rate of predation.

The Department of Conservation carries out rat control in areas where there are endangered native species, such as kokako and blue duck. The aim of this control is to keep rat numbers low enough to allow eggs to hatch and young birds to fledge. In areas where rat control has taken place, there have been observations of great recovery of seedlings, indicating rats also have an impact on vegetation.

Rats are widespread throughout New Zealand.

Methods of control

Trapping

For welfare performance of animal traps go to https://www.bionet.nz/control/pests-under-management/performance-traps/

Ideally, ‘traplines’ should about be 100m apart. Along traplines, traps or bait stations should be 50m apart. (Perimeter traps or bait stations, 25m apart). This will create a network of traps or bait stations. It is important to consider the ease of checking and maintaining the equipment. Use existing tracks where possible. Be sure to position traps and bait stations so that they are not easily accessible by children or stock. Bait stations and traps should not be placed in water.

Commonly used rat traps include the Snap-E and Victor snapback. Please nots that kill traps must be set in a tunnel or under a cover. Initially traps should be checked every 1-2 days. Once catch rate drops (after about 5-10 checks), traps only need to be checked once every 2-3 weeks. When rat numbers increase, the frequency at which traps are checked will also need to increase.

Check with your local council to find out what traps are best suited for your area. 

Poisoning

Poisoning is an effective and cheap way to get rid of rats outdoors. Most rat poisons are anticoagulants and, following a single feed, the rodent will die in five to 10 days. Assuming rat numbers are high during the initial control; bait consumption will be high and gradually reduce as rat numbers decline. At the end of the operation uneaten bait must be collected and removed from operational area. This reduces the chance of rats being exposed to poor quality or old bait and the time toxin is in the environment.

Bait stations can be made of draincoil or PVC pipe and allow rate easy access but limits access by non-targets. They also limit spillage protect the bait from the elements. To prevent non-target animals such as possums or native birds accessing the bait, use at least 500mm long lengths of draincoil. Secure the draincoil to the ground using wire pins. New stations will need time to weather in the elements before pre-feeding the stations. Check and remove old bait and refill bait stations every six weeks after the first initial knockdown.

Several types of rat poison are available for purchase from your local regional council. Check with them for further specific guidelines for your area.  

Prevention

There are some simple ways to make an environment less appealing to rats:

  • Remove any cover that rats can live in, including long grass or rubbish.
  • Get rid of potential food sources or store them in rat-proof containers.


Timing of rat control operations and monitoring 

Timing of control is critical and depends on what is being protected. For species protection, timing is dependent on when the species being protected is most vulnerable. To protect invertebrates and lizards, rats should be controlled year round. 

To gauge the success of your rat control, use ‘tracking tunnels’ before and after the control program. Record the number trapped or the amount of bait taken. Observations of rat browse on native fruits such as kohekohe, karaka, taraire and tawa will help to determine if your native forest is recovering.

Legal requirements 

For a list of legal requirements check out the legal requirements page

More information 

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Disclaimer

The information on this website is intended to provide information about pests and pest management in New Zealand. We've made every effort to make sure that the information set out in this website is accurate. If you have an update to the information listed here please contact us.

Photo credit: Reg Mckenna