Paul Ralph, a Dargaville-based Pest Management Officer for the Northland Regional Council, says most people are aware of the damage possums can do to Northland’s forests.
However, far fewer people realise that rats are also a serious environmental threat to the region.
“Rats will eat almost anything, including many endangered native species like lizards as well as insects, bird’s eggs and the birds themselves. They also have the potential to carry and spread a number of serious diseases.”
Mr Ralph says there are three species of rat in New Zealand, but only two – ship rat (rattus rattus) and Norway rat (rattus norvegicus) – are found in the wild in Northland. (The third species, the kiore or Polynesian rat, was introduced to New Zealand around 800-1000 AD with the arrival of Polynesians, but is now confined to a number of offshore islands and rarely found on the mainland.)
The Norway rat is the largest of the three rat species and arrived on ships with the first whalers and sealers around 1790. Also known as the brown rat, water rat, sewer rat or pouhawaiki, it is generally distinguished by its larger bulkier size and a heavier, shorter tail.
The Norway rat typically weighs 200 to 300 grams is about 250mm long, excluding its tail, “although some individual animals may greatly exceed this”.
“Norway rats are competent swimmers and are usually found close to water or waterways. They can climb, but rarely do. Burrowing is characteristic.”
The ship rat (also known as roof rat, black rat and European house rat) was the third rat species to establish itself in NZ, arriving on ships around 1870.
“They are slightly smaller than the Norway rat, with relatively larger ears and a longer, more slender tail, which approximately equals its head and body length. Unlike the Norway rat they are reluctant (though competent) swimmers and do not burrow.”
Mr Ralph says ship rats occupy areas less favoured by Norway rats and are the species most often seen in bush areas and living up in trees.
He says fortunately, rats can be easily controlled and – when combined with possum control – this gives added benefit to the environment.
”Rats are relatively easy to kill with poisons – mainly anticoagulants, which prevent the blood clotting. There are a number of brands and types available from most stock and station outlets.”
As rats tend to take food away and store it, rather than eating it on the spot, it is advisable to secure poison baits to prevent rats from removing them thus making them unavailable to other rats.
“Inside, baits should be laid along walls and in ceilings where rats are present. Outside, lay baits near burrows and tracks made by rats. Bait stations can be purchased or made from pieces of pipe and household containers.”
Traps – both live capture and kill versions - can be useful where rats are nesting in buildings.
“Traps enable rats to be disposed of, as opposed to poisoned animals which can die in an inaccessible spot and smell.”
Mr Ralph says people wanting advice on rat control should contact Northland Regional Council Pest Management Staff on 0800 002 004.