207.

Isarog Shrew Mouse

Archboldomys luzonensis

French: Rat de |'lsarog / German: Isarog-Archboldmaus / Spanish: Raton musarana de Isarog

Other common names: Mount Isarog Shrew Mouse

Taxonomy. Archboldomys luzonensis Musser, 1982,

“altitude of 6560 feet [= 1999 m] on Mount Isarog,” Camarines Sur Province, SE Luzon Island, Philippines.

Genus Archboldomys may belong to a clade of murines that also includes species of Apomys, Chrotomys and Soricomys . Two species formerly included in Archboldomys are now placed in Soricomys ( S. kalinga 3. and S. musseri). Holotype of A. luzonensis, collected by D. S. Rabor in 1961, was for

many years the only example, but recent surveys have greatly improved knowledge of its morphology, evolutionary relationships, and ecology. Monotypic.

Distribution. Known only from Mt Isarog, Luzon I, Philippines.

Descriptive notes. Head-body 101-111 mm, tail 66-80 mm, ear 1617 mm, hindfoot 27-29 mm; weight 31-36 g. Archboldomys species are small terrestrial murines having shorttail with conspicuous scales, each with three short hairs; small forefeet with small flat nail on first digit and relatively short, robust claws on the other four; narrow hindfeet with six plantar pads and relatively short claws on all five digits; small, dark ears with dense cover of fine dark hairs; relatively small eyes; soft, dense and slightly woolly fur that is dark and of same color on all parts of body; thin rostral vibrissae that extend back to slightly behind ears; mammae two on each side, both inguinal; and skull delicately constructed, but with moderately large, cuspidate molars, and distinctively upturned tip to nasal bones. The Isarog Shrew Mouse is the smaller of the two species of Archboldomys . It is further distinguished by its shorter, reddish-brown fur,its absolutely and relatively shorter tail and hindfeet,its larger tail scales (15-16 rows per cm), and smaller and less cuspidate molars. Chromosomal complement has 2n = 26, FN = 43, and the autosomes include eight pairs of large metacentric or submetacentric and four pairs of mediumsized to very small telocentric chromosomes. The X chromosome common to both sexes is a large submetacentric element; the other X chromosome in femalesis a large telocentric element. The Y chromosome is a medium-sized telocentric element.

Habitat. Evergreen tropical forests, including primary montane forest and mossy forest types, at elevations of 1350-1999 m.

Food and Feeding. According to L.. R. Heaney and coworkers, Isarog Shrew Mice feed on earthworms, insects, amphipods, and other invertebrates.

Breeding. Two pregnant females captured in late March and late April each had a single embryo. Males have quite large testes relative to body size, up to 11 mm x 6 mm.

Activity patterns. According to Heaney and coworkers, Isarog Shrew Mice are primarily, if not exclusively, diurnal. They forage in leaf-litter and moss on forest floor, often in well-defined runways beside fallen logs or in root tangles.

Movements, Home range and Social organization. Population density in 1993-1994 at ¢.1600 m on Mount Isarog was estimated at 4-5 ind/ha, making the Isarog Shrew Mouse the second most abundant small ground mammalafter the LeastPhilippine Forest Mouse ( Apomys musculus). One recapture of a female was made 92 m from original capture point.

Status and Conservation. Classified as Vulnerable on The IUCN Red List. Currently documented area of occupancy is less than 20 km” but this is contained within Isarog National Park. Heaney and his coworkers, writing in 2016, reported that recent surveys on nearby Mount Labo and Mount Malinao failed to detectthis species, although “additional, focused surveys at high elevation are needed.” Bibliography. Balete & Heaney (1997 2008), Balete, Rickart & Heaney (2006), Balete,Rickart, Heaney, Alviola et al. (2012), Heaney & Utzurrum (1991), Heaney, Balete & Rickart (2016), Heaney, Balete, Rickart, Utzurrum & Gonzales (1999), Musser (1982a), Musser & Carleton (2005), Rickart & Musser (1993), Rickart, Heaney, Tabaranza & Balete (1998), Rickart, Heaney & Utzurrum (1991).