This species was still abundant in 1897-1898 while Andrews was on Christmas Island (Andrews 1900). By the time he returned to the island in 1908, he was confident that it and the other native rat species, Rattus nativitatis, were extinct (Andrews 1909). Andrews (1909) speculated that introduced Black Rats R. rattus had brought an epidemic disease to the island that wiped out both native rats. Nearly 100 years later, the mystery was finally solved by Wyatt et al. (2008), who used ancient DNA methods on samples from museum specimens of these rodents collected during the extinction window (AD 1888–1908), and showed that endemic rats collected prior to the introduction of Black Rats were devoid of evidence of a pathogenic trypanosome (carried by fleas hosted on recently-introduced Black Rats).
To Andrews, the disappearance of such an abundant animal in such a short time had to be due to disease because R. rattus was not present over the entire island. It was unreasonable therefore to assume that the native species had been out-competed by R. rattus all over the island (Andrews 1909). Two predators had been introduced to the island by 1908, cat and dog, but these were far too few to rid the island of the rats (Andrews 1900, 1909). Although Christmas Island had an increasing human settlement at Flying Fish Cove, roads now crossed the island, and there was active phosphate mining, there was still a lot of native forest and even collectively these human disturbances were unlikely to have caused significant declines in the populations of Maclear's Rat (Andrews 1909). Andrews (1909) also relates anecdotal information that a medical officer on the island, Dr. McDougal, recalled frequently seeing "individuals of the native species of rats crawling about the paths in the daytime, apparently in a dying condition" in 1902-1904.
Pickering and Norris (1996) report on documents concerning Maclear's Rat that were uncovered at Oxford University, and specimens from the Zoological Collections, University Museum, Oxford University and the University Museum of Zoology, Cambridge. The documents include notes for a lecture by K. R. Hanitsch who visited Christmas Island for five weeks in 1904 and was unable to locate either species of native rat. Dr. Durham, a pathologist, visited the island from November 1901 to March 1902 and reported in expedition reports that he was told that R. rattus had been introduced to the island in 1899 by the S.S. Hindustan. Durham also collected 19 rat specimens. Pickering and Norris (1996) note that some of these specimens were of R. macleari, R. rattus, and some of varying degrees of hybrid between R. macleari and R. rattus. Hybridisation between the two species, with the implication that R. macleari was genetically swamped by R. rattus, was put forward as a contributing factor in the demise of R. macleari (Pickering and Norris 1996). However, hybridisation between the two species is unlikely given the phylogenetic distance between them, and apparently re-examination of specimens confirms that each belongs to one or the other species (Musser and Carleton 2005, Aplin 2008). This is further supported by the molecular studies of Wyatt et al. (2008).
Notes on the date of extinction / date last seen (1902-1904):
Because Durham collected specimens, some of which were R. macleari, in late 1901 and 1902, R. macleari must have become extinct after 1901.
McDougal was the last person to recall seeing native rats alive, albeit in the act of dying (Andrews 1909). These rats were probably R. macleari because R. nativitatis was the rarer of the two, as evidenced by the fact that Durham was unable to collect any specimens of R. nativitatis in 1901-1902. Andrews (1909) writes that McDougal's recollections are from 5-6 years before, but it is unclear whether he meant 5-6 years prior to his 1909 publication (putting the date at 1903-1904), or if it was 5-6 years prior to 1908 when Andrews was on Christmas Island (putting the date as 1902-1903 as Pickering and Norris (1996) interpret the anecdote). Because Hanitsch was unable to locate the species in 1904, it is likely that the species already had become extinct.