Rats eat the seeds and seedlings of plants thus reducing the level of natural regeneration in our native forests. Rats are known predators of lizard and bird eggs, chicks and baby reptiles and even the adults of some native species. Rats also damage crops, contaminate stock feed, damage buildings and carry diseases.
There are three types of rat in New Zealand:
- kiore or Polynesian rat (Rattus exculans)
- Norway rat (Rattus norvegicus)
- ship rat (Rattus rattus)
The kiore arrived in New Zealand in the canoes of the early Maori. Once widespread the kiore is now only found on Stewart Island and a few offshore islands. Although kiore do pose a threat to native fauna and flora this is not to the same degree as the Norway or ship rat.
When did they arrive here?
Norway rats were the first European rodents to become established in New Zealand when they arrived in the late 18th century on board North American and European sailing ships.
Where do they live?
These rats are now widespread throughout New Zealand. Norway rats are found in wild wetland habitats of rivers, streams, lakes, lagoons, swamps and estuaries and around human habitation in landfills, sewers, sea walls, wharves, where food is processed or stored, pig sties, poultry yards, cereal and root crops and along irrigation or drainage ditches.
What do they look like?
The Norway rat is the largest of the rats weighing 150-500g. It has a short body, with thick coarse hair coloured greyish brown on the back and pale grey underneath, and a thick tail, which is slightly shorter than the body. Norway rats are competent swimmers, capable of swimming 600m, earning them the name 'water rat'. These rats can jump 77cm vertically and 120cm horizontally. Sexual maturity is reached in 2-5 months and they have 3-6 litters each year containing 7-8 young. Where do they live?
Ship rats were slow to spread initially due to the establishment of the dominant Norway rat but today they are the most extensively distributed of the three rats and will live anywhere there is available food.
What do they look like?
The ship rat has a pointed muzzle, large eyes and ears, a sleek body with a long scaly tail. Rat colours can vary from black to slate grey to tawny above and grey or yellow below. Ship rats are excellent climbers and pose the greatest threat to our native wildlife.
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Options for the control of rats include:
- traps
- glue boards
- poison
- modification of environment
Traps and glue boards
- These control methods are most suitable for small rat infestations particularly in buildings where poisoned rats will smell as they decay.
- Traps are available from supermarkets and hardware stores.
Poisons
Most poisons available for rat control are anticoagulants.
These require feeding of the poisoned bait over several days and result in the death of the rat 5-10 days after eating the bait. Bait stations can be used to protect non-target animals from the poison and the poison from the weather. Baits should be placed near 'runs' or burrows.
Before using any poison read the poison label, comply with the instructions, and ensure you understand the symptoms and the recommended first aid treatment.
Modification of environment
- Removing cover that might harbour rats and potential food sources is a good deterrent.
- Rat proofing buildings will greatly reduce internal infestations from recurring.
Contact an Environment Bay of Plenty pest animal officer.
See Fact Sheet PA12 - Rats.
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