Fig. 12.—The Black Rat.
Rutland records how, in 1856, the district of Collingwood, on the western side of Blind Bay, was visited by a swarm, and in 1863 he was informed of a swarm on the Shotover, Otago. I have heard of this one also. Old miners used to tell how they were nearly eaten out of provisions by an invasion of rats. Repeated swarms occurred in Picton in 1872, 1878, 1880, 1884, and 1888. Rutland says, “These rat-swarms invariably take place in spring. A few of the animals appear in August; they increase in numbers till November, when all disappear again gradually as they came. While in a locality dead rats are seen lying about in all directions—on roads, in gardens, and elsewhere. Very few have any marks of violence on their bodies; nor have they died of hunger, since, on examination, they are generally found fat. In 1884, in Picton, forty-seven dead rats were found lying together under the floor of the sitting-room in one house. In another thirty-seven were found dead under the kitchen. The whole town was pervaded with the odour of dead rats. The average weight of a full-grown specimen is about 2 oz. The fur on the upper portion of the body is dark brown, inclining to black; on the lower portion white or greyish-white. They run awkwardly and slowly on the ground, but run very quickly on the trees. When suddenly startled or pursued they cry out with fear. The extremely few females that occur amongst the countless hordes is a fact that shows that, if breeding does take place at all during these periods of travel, it must be on a very limited scale.”
I think a probable partial explanation of this problem is that only the males migrate, while the females, which are producing young at that very season—the beginning of spring—remain in their usual haunts.
“They do little damage, their food being green vegetables. Though they enter dwellinghouses and barns, it is evidently not in quest of food, as shown by corn and other eatables being left untouched by them.” Rutland adds, “Among English country people, who have the best opportunity of observing them, it is commonly asserted that in litters of young rats the males produced outnumbered the females by about seven to one.”
Meeson describes a plague of rats in 1884: “Nelson and Marlborough—in other words, the whole of the extreme northern portion of the South Island of New Zealand—is enduring a perfect invasion. Living rats are sneaking in every corner, scuttling across every path; their dead bodies in various stages of decay, and in many cases more or less mutilated, strew the roads, fields, and gardens, pollute the wells and streams in all directions. Whatever kills the animals does not succeed in materially diminishing their numbers. Young and succulent crops, as of wheat and peas, are so ravaged as to be unfit for and not worth the trouble of cutting and harvesting. A young farmer the other day killed with a stout stick two hundred in a couple of hours in his wheat-field.” Among reasons suggested for the visitation he suggests the pressure of famine: “Last summer was very wet, and last winter very cold; the amount of snow lying on the high lands in the interior was very great. Another is the excessive increase in numbers, producing an intense struggle for existence.” It is thus seen that his conclusions are somewhat different from those reached by Mr. Rutland, who did not think that hunger was an impelling cause. He goes on to say, “I have examined many of these animals, and have not found a single female. One of my neighbours has examined two hundred of them, and a Maori, at the pa beyond Wakapuaka, one hundred, with the same negative result. Some females have, however, been taken, and in one case they were found breeding. He is more like a big field-mouse than a Norway rat; and besides being considerably smaller he is slightly darker in colour, and less malodorous. He climbs trees and flax-plants, and is phytophagous rather than carnivorous.”
Hutton, writing in 1887, said, “The rat appears to have invaded Picton at the end of March, and to have suddenly disappeared by the 20th April. Old Maoris recognized it as the rat they used to eat in former times, and said that swarming on to the lowlands periodically was always characteristic of it. These rats were often noticed climbing trees. In the Pelorus, where they stopped longer, they built nests, like birds, in trees.”
Kingsley, in 1894, records it as nesting on the branches of small trees, 4 ft. to 5 ft. from the ground, near Totaranui, and gives examples from Motueka, Riwaka, Collingwood, Nelson, and Taranaki. I myself have seen tall thorn hedges at Whangarei full of their nests—large, shapeless structures, which at first I thought must have been made by house-sparrows which had taken to building in hedges.
At the present time black rats are extraordinarily common about Christchurch. Mr. Speight, the curator, informed me three years ago that Canterbury Museum was infested with them. A good deal of the damage said to be done to orchards by opossums is almost certainly the work of the black rat.
Marriner reports that he met with grey rats at North-west Bay in Campbell Island, which Waite, of the Canterbury Museum, thought were probably specimens of Mus rattus.
The brown, or Norway, rat (Mus decumanus) is ubiquitous, and, though there is no record of its arrival in New Zealand, it no doubt arrived here in the earliest days of settlement. Early in last century Russell, or Kororareka, in the Bay of Islands, was the chief port of the young colony, and rats must have become very abundant there. Charles Darwin, who visited the Bay of Islands in 1835, says in his account of the voyage of the “Beagle,” “It is said that the common Norway rat, in the short space of two years, annihilated in this north end of the Island the New Zealand species.” Dieffenbach, writing some time later, said he never could obtain a native rat, “owing to the extermination carried on against it by the European rat.” There is no doubt that this species has had a considerable share in the destruction of the native avifauna, and it is also responsible for much of the difficulty experienced by acclimatization societies and private individuals in their attempts to establish introduced game-birds, but I do not think it is responsible for the disappearance of the Maori rat.