228.

Shaw Mayer’s Water Rat

Baiyankamys shawmayeri

French: Rat de Shaw Mayer / German: Shaw-MayerSchwimmratte / Spanish: Rata de agua de Shaw Mayer

Other common names: Shaw Mayer's Baiyankamys

Taxonomy. Baiyankamys shawmayeri Hinton, 1943,

“Baiyanka, Purari-Ramu Divide, south-east Bismarck Range, North-east New Guinea [= Eastern Highlands Province, Papua New Guinea], 6500 feet [= 1981 m].”

Genus Baiyankamys was established on a taxonomically mismatched cranium and mandible, resulting in diagnosis stressing a unique molar formula. B. shawmayeri has generally been treated as a synonym of Hydromys [= Baiyankamys] habbema, but widely allopatric distributions, coupled with multiple morphological differences, support specific distinction. Morphological contrasts between these species and members of genus Hydromys were clarified by K. M. Helgen in 2005. Monotypic.

Distribution. Mountains of E New Guinea from Doma Peaks E to vicinity of Mt Kaindi.

Descriptive notes. Head-body 130-153 mm, tail 148-185 mm, ear 12-17 mm, hindfoot 35-39 mm; weight 68-88 g. Baiyankamys species are plump, short-limbed, semi-amphibious murines with broad head, moderately long snout with numerous long,fine vibrissae, short rounded ears; fur on upperparts is very soft, dense, underparts paler; hindfeet proportionally large and broad, with partial webbing between toes; tail longer than headbody length, thickly furred, dark basally and with white tip. Dentition is characterized by delicate incisors,loss of third molars, and basined molar morphology. Shaw Mayer’s Water Rat has shorter white portion on tail (less than one quarter of length), less reduced ears (more than 12 mm), and slate-gray underparts. Molar teeth are slightly smaller than those of Mountain Water Rat ( B. habbema). Mammae two on each side, both inguinal.

Habitat. Most records are from streamsides within mountainous landscape that regionally supports lower and upper montane tropical forests. Habitat around highest elevation at which Shaw Mayer’s Water Rat has been recorded, at Lake Aunde (Mount Wilhelm, Western Highlands Province), is subalpine scrub and tussock grassland. Elevational range of precisely localized specimens is 1980 m (Baiyanka, Eastern Highlands Province) to 3597 m (Lake Aunde).

Food and Feeding. Stomach contents from Shaw Mayer’s Water Rat included aquatic invertebrates (insect nymphs and larvae, leeches and earthworms) and frogs.

Breeding. Mammary formula (two pairs) indicates small litter size. Individuals have been dug from burrows located in streamside banks.

Activity patterns. No information.

Movements, Home range and Social organization. No information.

Status and Conservation. Classified as Least Concern on The IUCN Red List. There is little anthropogenic disturbance in New Guinea at elevations above 2000 m.

Bibliography. Aplin, Dickman et al. (2008), Flannery (1995b), Helgen (2005), Hinton (1943), Lidicker (1968, 1973), Mahoney (1968), Menzies & Dennis (1979), Musser & Carleton (2005), Musser & Piik (1982), Tate (1951).