Origin of the Rat in the Kermadecs.
When first discovered by Europeans, Macauley Island was described as having a “great number of rats and mice” (Watts, 1789, p. 228). There is no similar record for Sunday Island, though this island is now overrun with the Pacific rat (Mus exulans), which could scarcely have been introduced by Europeans, who have been the only visitors to the group since its discovery, a little more than a hundred years ago, and who would have introduced,
if any, the more widely distributed and powerful grey and black rats. These, however, are unknown in the Kermadecs.
Remarking on Lieutenant Watts's narrative, Mr. Cheeseman says, “This would seem to prove that the species, whatever it may be, is truly indigenous” (Cheeseman, 1888, p. 163). Mr. O. Thomas, in his note on some rats collected on Sunday Island, says that the Pacific rat “has probably travelled from island to island in Native canoes, or on floating logs, &c.” (Thomas, 1896, p. 338). Now, if floating logs carried rats to the Kermadecs in the first instance, then the species would be truly indigenous, provided it had not been introduced through the agency of man to the country whence it migrated to the group.
The Kermadec Islands are, from a biological standpoint, oceanic in character. In order to reach the groups, therefore, rats must cross about six hundred miles (1,000 km.) of ocean, which is the distance to the nearest land. The time which would be taken by a floating tree drifting this distance negatives the possiblity of rats reaching the group in this manner.
The Pacific rat occurs in all the principal groups of islands in the Pacific Ocean. As many of the inhabitants of these islands used it as an article of food, it would often be carried intentionally from one island to another. Probably, however, it was more often carried accidentally in the Native canoes. Being a small, timid, and harmless animal, it would not be troubled much by the Native navigators, and this, possibly, may explain its wide distribution.
On Sunday Island there have been found from time to time stone axes of a similar pattern to those made by Maoris. Other evidence of Native occupation of the group is furnished by the large holes on the Terraces, which, from their position, number, and size, have evidently been made by some Native race. Probably they were chiefly ruas, or storehouses for food. In some of the larger holes, however, were large water-worn stones, no doubt brought from the beach below. These larger holes may be hangis where the Natives prepared their ti-root.
There is no doubt then that the Kermadec Islands were at one time inhabited by Natives, and it is by them, either accidentally or intentionally, that I consider the rat has in all probability been introduced.*
List of Works referring to Sunday Island Rat.
1789. Watts, Lieutenant: Chapter xx of “The Voyage of Governor Phillip to Botany Bay.” London.
1887. Smith, S. P.: “The Kermadec Islands; their Capabilities and Extent,” p. 24. Wellington.
1888. Cheeseman, T. F.: “On the Flora of the Kermadec Islands; with Notes on the Fauna.” Trans. N.Z. Inst., vol. 20, p. 163.
1896. Thomas, O.: Proc. Zool. Soc., 1895, p. 338.
1897. Waite, E. R.: “The Atoll of Funafuti, Ellice Group” (Mammals). Mem. Aust. Mus., 3, p. 165.
[Footnote] * In my paper on the “Vegetation of the Kermadecs” (Trans. N.Z. Inst., vol. 42, p. 173) I have included the candlenut (Aleurites moluccana) and the Polynesian ti (Cordyline terminalis) in the list of introduced plants, as they are not distributed generally in the forest, but are found only in habitable parts of Sunday Island, where they appear to be survivors of the abandoned cultivations of a Native race.