215.

Mount Isarog Shrew Rat

Rhynchomys isarogensis

French: Rhynchomys de I'lsarog / German: Mount-Isarog-Nasenratte / Spanish: Rata musarana de Isarog

Other common names: Isarog Rhynchomys, Isarog Shrew Rat, Mount Isarog Rhynchomys

Taxonomy. Rhynchomys isarogensis Musser & Freeman, 1981, Mt. Isarog, south-east peninsula of Luzon Island, Camarines Sur Province, Philippines.

Rhynchomys isarogensis was reviewed and compared with newly discovered species by D. S. Balete and colleagues in 2007, and a morphometric analysis accompanied by a molecular one allowed the description to be refined and its validity corroborated by Balete and coworkers in 2012. The karyotype was established by E. A. Rickart and L. R. Heaney in 2002. R. isarogensis is sister taxon of R. banahao. Monotypic.

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

Descriptive notes. Head-body 170-187 mm, tail 108-126 mm, ear 21-23 mm, hindfoot 37-40 mm; weight 110-156 g. Morphometric analysis showed that males are larger than females. The Mount Isarog Shrew Rat is very similar to other Rhynchomys representatives in having a long, narrow snout and head, tiny incisors and long vibrissae, and long hindfoot. Soft and dense pelage is grayish brown dorsally and nearly white ventrally. Tail is smaller than combined head-body length, unicolored, but darker dorsally. As with all Rhynchomys, skull displays an elongated narrow mandible and there are only two upper and lower molars. Females have two pairs of mammae. Chromosomal complement has 2n = 44, FN = 52.

Habitat. Montane and mossy forests between 1125 m and 1750 m. Mount Isarog Shrew Rats are more common in mossy forest than in montane forest.

Food and Feeding. Earthworms and other soft-bodied invertebrates (amphipods, larvae) are eaten by the Mount Isarog Shrew Rat, which shuns vegetable matter. These

shrew rats patrol pathlines in the forest underground in search of worms and other food.

Breeding. Three females each borea single embryo.

Activity patterns. Mount Isarog Shrew Rats are nocturnal and terrestrial.

Movements, Home range and Social organization. Mount Isarog Shrew Rats can move 50 m per day. Density is estimated at 2-5 ind/ha.

Status and Conservation. Classified as Vulnerable on The IUCN Red List. The Mount Isarog Shrew Ratis found in a protected area and populations are stable, but its known range covers less than 20 km?*.

Bibliography. Balete, Rickart, Heaney et al. (2012), Balete, Rickart, Rosell-Ambal et al. (2007), Heaney, Balete & Rickart (2016), Rickart & Heaney (2002).