212.

Blazed Luzon Striped Shrew Rat

Chrotomys silaceus

French: Chrotomys orné / German: Ockergelbe Streifenratte / Spanish: Rata musarana listada de Luzén

Other common names: Blazed Luzon Shrew Rat, Blazed Luzon Chrotomys, Blazed Striped Shrew Rat, Silver Earth Rat, Silver Chrotomys

Taxonomy. Xeromys (?) silaceus Thomas, 1895,

“highlands ofNorthern Luzon.” Restricted by O.Thomas in 1898 to “Monte Data, Lepanto, N. Luzon [Island], 8000 feet [= 2438 m],” Philippines .

Thomas's initial tentative referral of C. silaceus to the Australian genus Xeromys reflected its close external similarity to X.myoides and the presence of only two molarsin each series, which contrasted with the condition in species of Chrotomys . Soon after, in 1898,

Thomas erected a new genus, Celaenomys,for silaceus, although he acknowledged the close relationship with Chrotomys . The combination Celaenomys silaceus was usedby all authors until 1992, when G. G. Musser and L. R. Heaney documented the close affinity of silaceus to other species of Chrotomys; this has been fully substantiated by subsequent molecular studies. C. silaceus is locally sympatric with C. whitehead, which extends to lower elevations. Chrotomys and Rhynchomys of the Philippines were typically allied in the past with the Australo-Papuan water rats ( Hydromys etc.), mainly on account of dental similarities. Their closest phylogenetic affinities, as revealed by molecular studies, are with other, recently discovered Philippine shrew rats and mice of genera Archboldomys, Rhynchomys, and Soricomys, and with the less specialized Philippine murines of genus Apomys . Monotypic.

Distribution. Cordillera Central of N Luzon I, Philippines.

Descriptive notes. Head-body 136-173 mm, tail 97-121 mm, ear 19-23 mm, hindfoot 34-39 mm; weight 71-160 g. Chrotomys species are stout-bodied, semi-fossorial murines with short, strong limbs and a thick tail considerably shorter than head-body length; relatively small eyes; ears rounded and relatively short; forefeet proportionally large and with strong digits and heavy, nearly straight claws on second to fourth digits; hindfeet long and narrow, with small plantar pads and claws on all digits; cranium robust, with flask-shaped outline, forward-projecting upper incisors that are probably used for digging, short nasal bones terminating well behind level of incisors, and molars small, with occlusal pattern consisting of shallow “basins.” The Blazed Luzon Striped Shrew Ratis smallest member of genus, and has fur on upperparts short, dense, and velvety, hair length 10-12 mm on middle of back; color ation unlike that of other Chrotomys in absence of longitudinal stripes, instead having fur on back, head, and flanks usually a uniform dark gray, brownish gray, orsilvery gray, occasionally a faint pale line over shoulders; underparts a paler shade of gray or silver gray; transition between flanks and underparts gradual; white blaze sometimes present on forehead,sides of muzzle nearly black, vibrissae blackish gray, reaching to ears; eyes small, no dark ring; ears pale gray and sparsely furred. Feet have upper surfaces dark gray and well furred, except for digits that are unpigmented and bear white hairs; plantar surface of hindfeet with six pads. Tail is relatively short (66-79% of head-body length), skin brown above and white below, usually with short all-whitetip, scales small, in 16-19 rows per cm, each scale with three short, silvery hairs. Cranium is moderately robust but with relatively narrow rostrum and delicate incisors, small auditory bullae, molars proportionally reduced in size and usually only two in each series (occasionally three). Females with two pairs of mammae, both inguinal. Chromosomal complement has 2n = 44 and FN = 52, and includes two pairs of small metacentric, one pair of large submetacentric, one pair of large subacrocentric, and 18 pairs of acrocentric chromosomes,the last graded from large to small. The X and Y chromosomes cannot be distinguished from the autosomes and must be among the acrocentric series.

Habitat. Evergreen tropical forests, including transitional montane/mossy and mossy forest types distinguished in Philippine ecological literature, and occasionally found in shrubby vegetation near agricultural fields if these are close to forest cover. Elevational range 1800-2800 m.

Food and Feeding. Individuals kept briefly in captivity avidly consumed earthworms. The Blazed Luzon Striped Shrew Rat is reported as foraging for earthworms and other soil invertebrates by digging in leaf litter and humus.

Breeding. Five adult females have each carried two embryos.

Activity patterns. L.. R. Heaney and coworkers report that the Blazed Luzon Striped Shrew Rat is active primarily during day but also at night.

Movements, Home range and Social organization. Heaney and coworkers report that individuals kept briefly in captivity were docile.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The type locality on the Mount Data Plateau has been heavily modified by agricultural activity, and this species was notdetected during a resurvey in 2006. This species is more abundant in upper part of its elevational range. Where the Blazed Luzon Striped Shrew Rat and the Montane Striped Shrew Rat ( C. whiteheadi) co-occur,it is the former that tends to be the more abundant of the two.

Bibliography. Balete et al. (2012), Corbet & Hill (1992), Ellerman (1941), Heaney (2016e), Heaney, Balete & Rickart (2016), Heaney, Balete, Sarmiento & Alviola (2006), Jansa et al. (2006), Misonne (1969), Musser & Carleton (1993, 2005), Musser & Heaney (1992), Rickart & Heaney (2002), Rickart, Balete et al. (2011), Rickart, Heaney et al. (2011), Sanborn (1952a), Thomas (1895c, 1898b).