Rattus rattus species group. Reviewed by Musser and Califia (1982), who also summarized and provided references documenting the incorrect historical association of tiomanicus and the other synonyms listed here as subspecies of R. rattus. They also pointed out that careful study of inter-island variation among named forms of the R. tiomanicus complex is necessary before relationships among the insular populations can be discerned; more than one species may be represented in what is now viewed as R. tiomanicus. Miller’s (1942) blangorum from the Aceh region of N Sumatra, for example, was originally described as a species, then included in R. tiomanicus (Musser and Califia, 1982), and is here reinstated as a separate species (see account of R. blangorum).

Rattus mindorensis from Mindoro Isl in the Philippines; R. simalurensis from the islands of Babi, Lasia, Siumat, and Simalule, off the northwest coast of Sumatra; R. lugens from the Mentawai Arch., and R. adustus from Pulau Enggano (all islands off W coast of Sumatra), and R. burrus from some of the Nicobar Isls, are morphologically similar to the R. tiomanicus complex and should be considered part of it (Musser, 1986; Musser and Heaney, 1985). Whether they are species or island forms of R. tiomanicus can be determined within the framework of a systematic revision of the R. tiomanicus complex employing morphological and molecular data.

Distribution and ecology of R. tiomanicus on the small islands off the tip of N Sabah documented by Md Nor (1996). It is found primarily in the lowlands on Borneo but reaches 1700 m on slopes of Mt Kinabalu in Sabah (Md Nor, 2001, and references cited therein).