Rats and House Mice
Four species of rodents – three species of rats and the house mouse – belong to this group. The once abundant Maori rat, Rattus exulans (q.v.), is said to have reached New Zealand with the main Maori Migration of about A.D. 1350. It was highly prized as food. The kiore is at present restricted to a number of outlying islands, Stewart Island, and a few isolated localities in Fiordland. The disappearance of kiore followed closely on the arrival of the black (R. rattus) and Norwegian (R. norvegicus) rats from Europe. These two species, which probably came in the ships of Captain Cook and those of early sealers and whalers, are now firmly established on the two main islands and Stewart Island. In general, the Norway rat is found in towns and near piggeries, fowl houses, watercourses or ponds in the country; the black (or ship) rat inhabits the high floors of buildings in towns and is also widespread in native (especially podocarp) forests.
The European house mouse (Mus musculus) is widely distributed throughout the country, having been trapped up to an altitude of 1,300 metres. Although often found in or close to houses, it can survive in the absence of man, as its existence on Auckland Islands shows. Occasional plagues of mice are reported every few years in various parts of the country, particularly in the South Island. Both the ship and Norway rats and also the house mouse, being omnivorous, act as scavengers, but they also destroy food stock and buildings, and foul water mains. Overseas, the black rat carries bubonic plague through the Indian rat flea (Xenopsylla cheopis), and the Norway rat carries Leptospira pomona of cattle.
The Quarantine and International Health Regulations and the Health Act of 1920 cover rat control in New Zealand. All overseas ships are inspected and those without current “deratisation” certificates and which show evidence of rats are fumigated under the supervision of Health Inspectors. Some cities, like Wellington or Auckland, maintain full-time rat catchers. In many other towns and boroughs rat control is left to the occupier of premises, with occasional checks by the Sanitary Inspector under the general supervision of a Health Inspector. Traps, fumigation, and various poisons are used; these have been largely replaced by proprietary poisons containing warfarin. This has usually led to a general reduction of rat and mouse infestation in built-up areas.