231.

Broad-headed Tree Mouse

Chiruromys lamia

French: Chiruromys a téte large / German: Breitkopf-Baummaus / Spanish: Ratén arboricola de cabeza ancha

Other common names: Broad-headed Chiruromys, Broad-skulled Tree Mouse

Taxonomy. Pogonomys lamia Thomas, 1897,

“Ighibirei” (= lower Kemp Welch River, Central Province, Papua New Guinea).

Although C. lamia was originally described in Pogonomys, O. Thomas allied it with forbesi and distinguished the two as the “ Chiruromys section of the genus.” Form Pogonomys kagi, described in 1951 from 1525 m in the Owen Stanley Range, and differentiated from lamia by its “much smaller foot, softer silkier hair, white instead of buff underparts, shorter incisive foramina, and smaller teeth,” is generally treated as a synonym of kagi. E. Dennis and J. I. Menzies in 1979 referred a series from 2300 m on Mount Simpson in the Maneau Range to kagi, demonstrated some morphometric contrast between this group and typical lamia, and recommended treating kag: as a montane subspecies of lamia; this needs to be tested with input from genetics and/ or additional field observations to ascertain nature of any elevational contact between the two forms. Most records are from elevations above a larger congener, C. forbes, and there are no known instances of sympatry. Possibly sympatric with C. vates in the Astrolabe Range. Currently regarded as monotypic but in need of further assessment.

Distribution. Papuan Peninsula of New Guinea, including Astrolabe, Owen Stanley (W to Mt Albert Edward and Kokoda Gap), and Maneau ranges (Mt Simpson, Mt Mura, Mt Suckling, and Mt Dayman).

Descriptive notes. Head-body 97-120 mm, tail 147-172 mm, ear 17-19-8 mm, hindfoot 23-625 mm; weight 40-5-56 g. Species of Chiruromys are small to medium-sized arboreal mice with short, broad head, soft dense fur; eyes relatively large, more forward-facing than typical for Murinae; long, coarsely scaled tail with terminal, upwardfacing prehensile pad; and molars with complex crown patterns, retaining many primitive murine features. The Broad-headed Tree Mouse, one of the smaller members of genus, has fur on upperparts soft and woolly, hairs on back measuring 11-13 mm, general color dull fawn grizzled with silvery, the latter produced by pale guard hairs projecting 2—4 mm, bases of body hairs dark gray; fur on flanks and outer surfaces of limbs is yellowish brown; fur of underparts to throat and inside of limbs white or very pale buff to bases, sharply contrasting with flanks; head is strikingly patterned, lips white, cheek white in front and cinnamon behind, vibrissal pads gray, black mask around each eye and extending forward onto sides of snout; vibrissae dark and very long, extending back past shoulders; ears relatively short, rounded and dark, thinly furred. Feet are unpigmented, hairs white or pale buff, 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 present on all digits. Tail is very long (134-145% of head-body length), uniformly brown,scales relatively small (12-15 rows/cm), hexagonalto diamond-shaped, unkeeled, strongly overlapping; each scale with three hairs equal in length to 2-2-5 scales, overall appearance moderately hairy; tail tip with prehensile pad 30-35 mm long on uppersurface. Cranium has very short rostrum, strongly flaring zygomatic arches, molars more reduced than in C. forbesi . Mammae three on each side, one axillary and two inguinal.

Habitat. Most records of the Broad-headed Tree Mouse are from primary evergreen tropical rainforest, but T. Flannery mentioned encounters in “extremely degraded forest” and in “a Ficus tree growing near a village.” Elevational range probably 1200-2300 m, within zone of lower montane rainforest in New Guinea, though holotype may have come from a lower elevation on Kemp Welch River. If found below 1300 m,it may occur also in lowland hill forest.

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

Breeding. Broad-headed Tree Mice occupy nests in tree hollows, and information on breeding comes from field observation on such groups. In the Agaun area of Milne Bay Province, in August, individuals were encountered alone and in groups. Groups comprised 4-7 individuals, in all cases including at least one adult of each sex and some young. One group contained two adult males, while another included two adult females. In two of four groups, the young varied too much in body size to represent young ofa single litter, but it is not known whether they were offspring from consecutive litters from a single female or evidence of nestsharing by more than one female.

Activity patterns. Although Broad-headed Tree Mice can be locally common, they are rarely trapped on the ground. Most specimens have been taken from nests situated in natural or modified tree hollows, and it is possible that activity is more or less confined to canopy.

Movements, Home range and Social organization. Like other Chiruromys, the Broadheaded Tree Mouse nests communally, with group size and composition reviewed above. Some of the young in nests have been close to full adult size, which suggests unusual level of parental investment compared with most other Murinae.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The lower part of the elevational range of this species corresponds with a zone of extensive habitat modification on the Southeast Papuan Peninsula, a result of long-term subsistence agriculture. Although significant patches of lower montane rainforest are still present through this area, some are potentially vulnerable to forestry activities.

Bibliography. Aplin (2016s), Dennis & Menzies (1979), Ellerman (1941), Flannery (1995b), Laurie (1952), Laurie & Hill (1954), Menzies & Dennis (1979), Musser & Carleton (1993, 2005), Rimmler (1938), Tate (1951), Thomas (1897c).