239.

New Britain Water Rat

Hydromys neobritannicus

French: Hydromys de Nouvelle-Bretagne / German: Neubritannien-Schwimmratte / Spanish: Rata de agua de Nueva Bretaria

Other common names: New Britain Hydromys

Taxonomy. Hydromys neobrittanicus [sic] Tate & Archbold, 1935,

“Bainings, Balayang, Wide Bay, New Britain, Solomon Islands,” Papua New Guinea .

Initally described from a single specimen, H. neobritannicus was listed byJ. R. Ellerman in 1941 as a subspecies of H. chrysogaster, but G. H. H. Tate defended its species status in 1951 on strength of its unique blackish-brown upperparts and its unusual tail coloration that features both a white tip and white interstitial spot or “belt” around middle of its length. White interstitial tail spotting is reported by A. Searle as one of the most frequent color coat variants associated with pathologicalconditions in mammals. C.

M. Kemper and L. H. Schmitt in 1988 described emergence of interstitial spotting within a laboratory colony of the Conilurus penicillatus but noted the absence of this condition among wild populations. T. F. Flannery in 1995 reported a second specimen of a Hydromys from “New Britain”, putatively collected on north coast in 1886, but noted thatit lacked the white belt on the tail and also had a more rufous venter than the holotype. G. G.Musser and M. D. Carleton in 2005 recommended that neobritannicus be maintained as a full species pending more detailed studies of the geographically widespread, large-bodied group within Hydromys . The island of New Britain harbors endemism among other genera of Murinae, as well as other groups of vertebrates. Monotypic.

Distribution. New Britain I, Papua New Guinea.

Descriptive notes. Head-body 288 mm, tail 289 mm, ear not recorded, hindfoot 60 mm. No specific data are available for body weight. Species of Hydromys are plump, short-limbed, semi-amphibious murines with hindfeet that are moderately long and broad and have partially webbed toes. The New Britain Water Rat is one of the largest of the genus. Fur on upperparts is very soft and dense, contour hairs measuring 10-13 mm on middle of back. Upperparts are very dark brown, flecked with black owing to presence of numerous short guard hairs, and with glossy sheen; fur on flanks, limbs, and sides of head paler brown. Underparts are dark brown,slightly paler on throat and chin, and on lower abdomen. Head is robust, with no contrasting coloration. Vibrissal pads dark; vibrissae numerous, moderately thick and very long, reaching back to shoulders. Eyesslightly reduced; ears moderately large, thinly furred, and with pale brown skin. Feet have dense covering of short black hairs above, extending onto digits; forefeet with nail on small first digit, and robust claws on other digits; hindfeet very elongate and broad, all digits with strong, recurved claws, second to fourth digits united by band of conspicuous webbing. Tail of holotype equals combined length of head and body, is rounded in cross-section and somewhat thickened for entire length; tail densely furred to tip, individual hairs extending for length of many scale rows,fur black apart from terminal 15% and a short “belt” at mid-length, which are pale buff, almost white; tail terminates in short tuft. Cranium is robust, with square braincase, broad interorbital region, and short, broad rostrum. Molars reduced to two per quadrat, crowns with “basined” cusp arrangementtypical of Hydromys, molars larger than in any other Melanesian Hydromys but size is matched by some Australian populations of H. chrysogaster . Mammae two on each side, both inguinal. According to Flannery, the possible second specimen from New Britain lacks the white belt on tail and has a “red belly.” The Common Water Rat ( H. chrysogaster) shows much color variation acrossits wide geographic range, yet nowhere else is there a precise match for either of the two color forms observed in New Britain.

Habitat. Natural vegetation cover of New Britain is evergreen tropical rainforest, with lowland and hill rainforest associations from sea level to ¢.1000 m and increasingly mossy, montane communities at higher elevations. Parts of New Britain are karstic and havelittle surface drainage, but Gazelle Peninsula and northern lowlands are dissected by numerous streams and rivers that would provide suitable habitat for a largebodied waterrat.

Food and Feeding. No information.

Breeding. No information.

Activity patterns. No information.

Movements, Home range and Social organization. No information.

Status and Conservation. Classified as Data Deficient on The [UCN Red List. The lowland forests of New Britain were extensively cleared for plantations during late 19" and early 20™ centuries, with copra the original crop, but palm oil becoming more prevalentin recent decades. Despite widespread conversion of lowland habitats, riparian environments on New Britain often support a belt of more or less original forest, and this can retain high biodiversity. Populations of the New Britain Water Rat could persist in any of these habitats, aswell as in the hill and montane forests of the inland ranges which are subject to logging activities but remain primarily forested. Recent fieldwork on New Britain, such as surveys reported by S. J. Richards and G. B. Gamui in 2011, has focused on the karstic ranges and much less attention has been given to remnantforests of lowlands.

Bibliography. Aplin & Opiang (2011), Ellerman (1941), Flannery (1995a), Gerrie & Kennerley (2016j), Helgen (2005), Kemper & Schmitt (1988), Musser & Carleton (1993, 2005), Richards & Gamui (2011), Searle (1968), Tate (1951), Tate & Archbold (1935b).