Rattus detentus Timm, Weijola, Aplin, Flannery, and Pine, 2016

Pine, Ronald H., Mack, Andrew L. & Timm, Robert M., 2017, Marsupials And Rodents Of The Admiralty Islands, Papua New Guinea, Occasional Papers of the Museum 352, pp. 1-30 : 21-22

Rattus detentus Timm, Weijola, Aplin, Flannery, and Pine, 2016

Admiralties Rat

This recently described species, so far as known endemic to Manus and probably adjacent Los Negros, is the subject of a recent description and biogeographical analysis by Timm et al. (2016).

In 1988, Tim Flannery, while on Manus ( Flannery 2011), was told that there were two species of rat on the island, besides the ones he knew were introduced commensals. One was described as a red-pelaged arboreal rat and the other as a terrestrial rat with a white-tipped tail. Flannery succeeded in acquiring the first, which was M. matambuai .

Subsequently, archeological excavations at the Pamwak rock shelter on Manus turned up jaws and teeth of an early to late Holocene age rat that was variously identified by Williams (1999) as Rattus praetor and R. mordax . Flannery (1995b) examined these specimens and identified them as being of what he later described (2011:97) as “a formidable, hitherto unknown rat with a powerful bite.” Flannery (1995b:38) wrote, concerning this rat, “A large species of Rattus , probably representing an undescribed species, persists into the most recent levels…” of the Pleistocene Pamwak deposits—see also White et al. (2000).

In 2002, Ann Williams acquired from local people on Manus a nearly complete skeleton and a mandible of a second specimen, which came to the University of Kansas. Although the skeleton and isolated mandible are clearly from adults of the same species, the mandible is from what must have belonged to a larger individual than the other. Measurements of greatest distance between posteriormost point of alveolus of incisor and posterior edge of coronoid process are, respectively, 26.8 and 29.7. Flannery identified these two specimens as representing the same species as the undescribed rat from the Pamwak site. In 2012, Valter Weijola acquired an entire specimen which became the holotype of Rattus detentus . This species is presumably the same animal as the large terrestrial rat with a white-tipped tail of which Flannery (2011) had written, although the holotype, the only specimen for which external anatomy is known, does not have a white-tipped tail. It should be noted that one of the two recent specimens of Melomys matambuai , which have complete tails, has a white-tipped tail. However, according to Flannery (2011), and as noted earlier, the locals distinguish between a red, arboreal rat ( M. matambuai ) and a large terrestrial rat, and it was the latter that was said to have the white-tipped tail.

In 2014, Aplin (see Aplin et al. 2015), who had, by this time, studied not only all three recently collected specimens, but also the specimens from the Pamwak site, made special efforts to find this rat on Manus. In this he failed, although he did find a burrow system which he thought had probably been excavated by this species. Other signs of its presence, which Aplin expected to find if the species was at all common, were not found. This apparent rarity is in contrast with what locals told Valter Weijola when they were shown pictures of the future holotype. They claimed that the species is widespread on Manus and also occurs on Los Negros ( Timm et al. 2016).

Locals told Weijola (in litt.) that these rats often eat tapioca roots and pineapples in the gardens and fallen Canarium indicum ( Burseraceae ) nuts in the forest. The holotype was caught in an unbaited snare set by locals targeting bandicoots and rats. Unbaited snares were set along trails made by small mammals through undergrowth and often exiting near small streams. Traps set for monitors ( Varanus indicus ) and baited with fish were also sometimes raided and the lines cut off with a clean snip, which local trappers insisted was the work of rats rather than bandicoots, because the latter supposedly chew the line off. These anecdotal observations and conclusions suggest that R. detentus , like many other species of Rattus , has a rather wide dietary range. The rats themselves are said to be often hunted for food, particularly in the central parts of the island.

Timm et al. (2016) provided detailed information concerning the biogeographical features of Manus and vicinity, as they relate to the presence of R. detentus on Manus.