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  Environment » Natural Resources » Biodiversity » Native birds - Hamilton Halo » Pest control

Pest control

On this page: Rats, Possums


Rats feed on lizards, young plants, seeds, bird eggs and chicks, they also threaten other native species as they eat invertebrates, frogs and a variety of fruit. Controlling rats is the responsibility of land owners, however Waikato Regional Council is happy to provide advice to anyone who wishes to undertake rat control on their property.

There are two introduced European rat species in New Zealand.

Norway rat

Rattus novegicus, commonly known as the norway rat, water rat or brown rat, is the largest rat in New Zealand.


  • Short body and heavy tail, with the tail being slightly shorter than the combined length of the head and body.
  • Usually weighs 150-300 g, but can grow to more than 500 g.

Norway rats are competent swimmers and are commonly called ‘water rats’. This ability enables them to colonise offshore islands. In favourable conditions a crossing of 600 metres is possible.

Ship rat

Rattus rattus, commonly known as ship rat, root rat or black rat, is the most widespread rat in New Zealand.


  • The tail is longer than the combined length of the head and body.
  • Pointed muzzle with large ears.
  • Normally weigh 130-170 g.

Although rarely seen, ship rats are the biggest threat to breeding birds as they are exceptional tree climbers.

Watch our video of ship rats predating on native birds:

Signs of rats

  • Rat droppings – 10 mm spindle shaped.
  • Unusual smells - an ongoing rat problem can create a stale smell.
  • Holes - which appear in the garden, approximately 7-12 cm in size with a pile of earth near the entrance.
  • Rat runs - a continuous depression in grass or other low vegetation, a smooth pathway may be visible on bare earth.
  • Gnawing - often to the bottom of wooden doors and sheds.
  • Scattering - of compost being dragged out of bins or heaps.

Rat control

Making your backyard unfavourable to rats is probably one of the simplest means of control. Clearing your backyard of rubbish or any scrubby weed areas, as well as enclosing your compost heap, will mean that rats will have less habitat to live in on your property.

The most effective time for control is in the winter and spring. Rat ‘snap traps’ are available from hardware stores and some supermarkets. Locate traps in places where rats are likely to live, or where signs of rats are seen. Bait traps with peanut butter or chocolate, ensuring the bait is firmly attached to the bait pedal. If traps are placed outside they need to be covered or placed in a tunnel to avoid accidents by pets or children.

Some rat specific baits, such as ‘Natural No Rats’, have no secondary poisoning effects, making them a much safer option for use around cats and dogs. Other bait such as ‘Pestoff’ is effective on both rats and possums. Extreme caution should be taken when using any poison around pets – not just your own but your neighbours’ too. Bait stations should always be used when using any bait. Rat bait and bait stations can be purchased from farm supply stores, hardware stores and some supermarkets.


Possums affect native birds by preying on their eggs and young, and competing with native birds by eating young leaves, flowers and fruit. They also ruin fruit trees and roses, carry bovine Tb, and generally cause a nuisance. Controlling possums is the responsibility of land owners, however Waikato Regional Council is happy to provide advice.

Signs of possums

Browsing possums often leave behind distinctive signs, such as discarded and partially eaten leaves, flowers and fruit. They often leave behind the leaf stalk, base and mid-rib and tattered leaf remains. Heavy and persistent possum browsing will kill a tree.

Other possum signs to watch for include:

  • ‘runs’ (tracks) used nightly by possums travelling to and from feeding areas (most obvious in pasture)
  • claw marks on trees, fence posts and gates
  • bark bites (small horizontal marks) on trees
  • possum droppings scattered under food trees and in the forks of trees, the droppings are around 2.5 cm long and slightly thicker than a pencil.

Possum control

Waikato Tree Trust have Timms traps available for gully restorers to borrow. Timms traps are lightweight and easy to set. They can effectively control possums in small to moderate sized areas, such as urban gardens and gullies.

When using Timms traps make sure that you:

  • keep fingers clear of the front opening at all times
  • set traps in the evening and bait with a piece of fruit, such as quarter of a fresh apple or orange, or pieces of carrot. Don't use meat or fish as bait as it will attract cats to the trap.
  • keep family pets indoors while the trap is set and inform neighbours where traps are set so they can do the same
  • release the set trap early morning
  • do not leave set traps in areas where inquisitive children and pets can access them
  • replace bait every two days. 

To borrow a Timms trap email Kirsten Gerry or phone 07-8566563 (please leave voice message if not available).

Check out our information on possums.

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