232.

Lesser Tree Mouse

Chiruromys vates

French: Petit Chiruromys / German: Kleine Breitkopf-Baummaus / Spanish: Raton arboricola menor

Other common names: Lesser Chiruromys

Taxonomy. Pogonomys vates Thomas, 1908,

“Madeu, upper St. Josephs R. [= Angabunga River], about 50 miles [= 80 km] N. E. of Hall Sound, British New Guinea [= Central Province, Papua New Guinea]. Alt. 2000-3000’ [= 610-914 m].”

Although O. Thomas described C. vates as a species of Pogonomys, he clearly perceived its special affinity with lamia of the Southeast Papuan Peninsula. E. Dennis and J. I. Menzies in 1979 united these species and forbes: in genus Chiruromys, an arrangement followed by all subsequent authors. Molecular studies of the intergeneric relationships of Chiruromys have been based on samples of C. vates, which is far better represented in recent collections than is either C. forbesi or C. lamia . There are no definite instances of co-occurrence with congeners, but it may be sympatric with one or the other in Astrolabe Range. Unpublished morphological studies by K. P. Aplin suggest likely presence of a cryptic species within C. vates, with elevational segregation. Currently regarded as monotypic but in need of further assessment.

Distribution. Hinterland of Gulf of Papua, from Lake Murray and upper Fly River catchment E to Astrolabe Range and Kokoda Gap area of Owen Stanley Range, New Guinea.

Descriptive notes. Head-body 84:5-126 mm, tail 128-183 mm, ear 13-5-19 mm, hindfoot 22-26 mm; weight 23-68 g. Chiruromys species are small to medium-sized arboreal mice with short, broad head, soft and dense fur; eyes are relatively large, more forwardfacing than typical for Murinae; long, coarsely scaled tail with terminal, upward-facing prehensile pad; and molars with complex crown patterns, retaining many primitive murine features. The Lesser Tree Mouse, one of smaller members of genus, has fur on upperparts soft and woolly, hairs on back measuring 8-11 mm, brightly colored with orange to pale brick-red on back, with bases of hairs dark gray, middle of back flecked with black owing to black guard hairs that project ¢.2 mm through fur; fur on flanks is paler, yellowish brown, and with diminishing black flecking; fur on underparts to throat and inside of limbs is white to bases, sharply contrasting with flanks; head strikingly patterned, lips and cheek white, vibrissal pads gray, black mask around each eye and extending forward onto side of snout; vibrissae dark and very long, extending back past shoulders; ears relatively elongate, with distinctly pointed tips, skin pale basally and darker distally, thinly furred. Feet unpigmented, hairs white, claws short, pale, and with strongly curved tips, plantar pads broad; forefeet with claws on four digits, flat nail on inner digit; hindfeet short and broad, well suited to climbing, claws on all digits. Tail very long (134-160% of head-body length), uniformly brown, scales relatively large (8-10 rows/cm), hexagonal to diamond-shaped, unkeeled, strongly overlapping; each scale with three hairs equal in length to 1-1-5 scales, overall appearance mildly hairly; tail tip with prehensile pad 20-25 mm long on upper surface. Cranium has very short rostrum,strongly flaring zygomatic arches, molars more reduced than in C. forbes, similar to C. lamia . Mammae three on each side, one axillary and two inguinal. Karyotype is 2n = 44, with two pairs of large submetacentric autosomes and remainder mostly acrocentric, one small submetacentric (probably produced by pericentric inversion on pair 4), large submetacentric X chromosome; Y chromosome unknown. Spermatozoa with very long tail (152 pm) and the mid-piece almost two times as long as in most other Australo-Papuan Murinae, sperm head quite long (11 pm), with short (4 pm) apical hook, and shorter (3 pm) paired accessory ventral hooks formed of same cellular components as in Australian Hydromyini .

Habitat. Geographic range correspondsto a particularly high rainfall zone, which supports evergreen tropical rainforest, including areas of lowland alluvial rainforest and swamp forest, lowland hill rainforest, and lower montane rainforests above c.1000 m. Within this broad landscape, the species is recorded from both primary forests and secondary forests, and it may be limited mainly by availability of suitable tree hollows for nesting. Elevational range of modern specimens is from near sea level to 1500 m, with higher-elevation record at 2200 m from a contemporary owl roost deposit in a cave in Hela Province. Most records come from hill to lower montane elevations, but this probably reflects distribution of sampling effort. Not yet recorded from within extensive mangrove forest communities of lower Fly, Kikori and Purari River deltas.

Food and Feeding. Dental morphology suggests a general dietary focus on fruits and leaves.

Breeding. Lesser Tree Mice occupy nests in tree hollows, and information on breeding comes from field observations on groups and dissection of females taken from these. The most detailed data come from fieldwork by P. Dwyer in 1979-80 at 850-1200 m on Mount Sisa in Southern Highlands Province, and from fieldwork by Aplin and others in 1984 on the Karimui Plateau, Chimbu Province, and in 1985 on Sisa. In both areas, dissection of females revealed 1-3 embryos (modally, two). Smallest pregnant female

weighed 37 g, largest nulliparous female was 40 g. Many adult females captured on Karimui Plateau in April and early May were pregnant or lactating, and in some cases both, indicative of postpartum estrus and birth of sequential litters. At Mount Sisa, high proportion of adult females were pregnant in March and in June—October, and fewer in May. Breeding activity thus occurs through at least part of the local “cloud season” (April-September, when average temperaturesslightly lower and cloud cover and drizzle more persistent) but is not confined to this period.

Activity patterns. Although the Lesser Tree Mouse can be locally common,it is rarely trapped on ground. Most specimens have been taken from nests in natural or modified tree hollows, and it ispossible that activity is more or less confined to canopy. A few have been captured by hand at night from understory shrubs and samplings, and there are a few instances where local landowners have reported the digging of individuals or groups from burrows.

Movements, Home range and Social organization. Lesser Tree Mice nest communally. Three groups recorded on the Karimui Plateau were as follows: an adult male-andfemale pair with a half-grown female (23 g); an adult female (pregnant) with two young of contrasting sizes (17 g and 34 g); and an adult female with two young of contrasting sizes (25 g and 9 g). In Mount Sisa area, Aplin recorded an adult male-andfemale (pregnant) pair; three examples of adult male-and-female pairs with one or two young; and one group of two adult males, a single female, and three young. Dwyer’s observations on Sisa included similar adult pairs with young, a group of seven individuals including both adults and young, and a group with three adult females (two pregnant) with two young of contrasting sizes (9 g and 18 g). In both areas, some of the associated young have been close to full adult size, which suggests unusual level of parental investment compared with most other Murinae. On MountSisa, observations of groups occupying tree hollows were made throughout year.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The upper part of the elevational range of the Lesser Tree Mouse corresponds with a zone of extensive habitat modification in some parts of hinterland of Gulf of Papua,a result of long-term subsistence agriculture. This species does, however, remain common even in heavily utilized landscapes, provided that some mature trees are retained. Significant areas in Western and Gulf Provinces are currently experiencing forestry activity in primary lowland rainforest habitats.

Bibliography. Aplin (2016t), Breed (1984), Breed & Aplin (1995), Dennis & Menzies (1979), Ellerman (1941), Hide et al. (1984), Laurie & Hill (1954), Menzies & Dennis (1979), Musser & Carleton (1993, 2005), Rimmler (1938), Tate (1951), Thomas (1908).