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There are two common species of rat in New Zealand mainland; Norway rats and shiprats.
Norway rats are the larger of the two European rats found in New Zealand. Their coats are grey-brown and shaggy with a pale underside. They are distinguished from the ship rat in that the tail, which is about 180 mm in length, is thick and shorter than the body, which is about 200 mm in length.
Ship rats are smaller than Norway rats but their tails are larger and thicker and longer than their bodies.
Rats are mainly nocturnal. They have a varied diet that includes native birds, eggs and chicks, invertebrates, frogs, and lizards. They eat large quantities of native seeds, either from the ground or straight from the tree (in the case of ship rats, which can climb high into the canopy). Norway rats are common in wet habitats and urban areas. Ship rats are found in most habitats and they are the most abundant and widespread rat on mainland New Zealand.
Since their arrival in New Zealand, Norway rats and ship rats have had significant impacts on native flora and fauna. They have been implicated in the decline of many native species including the bellbird (korimako), robin (toutouwai), stitchbird (hihi), saddleback (tiekie), native thrush, parakeets (kakariki), flightless weevil, and giant weta.
Rodents are prolific breeders. Rats can breed throughout the year if conditions are suitable, with a female producing up to five litters a year. They can live for 3 years but wild animals probably live for less than a year.
Options for controlling rats include:
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.
Several types of rat poison are available for purchase from the Northland Regional Council. Ratabate®, and Ditrac® are some of the recommended rodenticides available.
Purpose built rat-bait stations keep the bait dry and protect non-target animals (like pets and birds) and to shield the poison from the weather. You need to use enough bait stations for the area you are trying to control – space your bait stations at 100-metre intervals.
Where to buy
You can buy bait stations from the Northland Regional Council and most farm supply stores, or make them from a piece of drainage pipe or similar material.
Using bait stations
Care with poisons
Victor® trap.Trapping is best suited to small rat infestations. It is particularly good in buildings, where using poison and having rats die inside is not ideal.
One of the most effective and easy-to-use rat traps available is the Victor® trap – peanut butter works well as bait. These traps are available from the Northland Regional Council and some hardware stores. Trap covers can be made out of coreflute (the material that real estate signs are made of). These keep the bait dry and prevent other animals being caught. These should be blocked at one end and tall enough that your traps can operate properly. Traps need to be checked and baited regularly.
There are some simple ways to make an environment less appealing to rats: