Haeromys pusillus

222.

Sundaic Ranee Mouse

Haeromys pusillus

French: Haeromys pygmée / German: Palawan-Zwergbaummaus / Spanish: Raton rani de Sonda

Other common names: Lesser Ranee Mouse, Sundaic Haeromys

Taxonomy. Mus margarettae pusillus Thomas, 1893,

“Mount Kina Balu [Kinabalu, Sabah, Malaysia], 1000 feet [= 305 m].”

Taxon pusillus was described as a subspecies by O.Thomas in 1893 butlisted as a full species in 1911 when he specified the content of Haeromys. It was treated as a subspecies by J. R. Ellerman in 1941, but returned to species level by G. B. Corbet and J. E. Hill, an action endorsed by G. G.Musser and almost all subsequent authors, although J. Payne and coworkers in 1985 treated pusillus as conspecific with H. margarettae. A specimen from East Kalimantan reported as H. margarettae by Lord Medway in 1977 was later discounted by Musser and M. D. Carleton in 1993. Musser and C. Newcomb in 1983 referred specimens from Palawan Province, Philippines,to a distinct but unnamed species. This taxon was listed by L.. R. Heaney and coworkers in 1998 as Haeromys sp. A. Musser and Carleton in 2005 referred this population to H. pusillus, pending more detailed assessment, and this position is followed here. Treated as monotypic but in need of further assessment.

Distribution. Known from a few localities in N & E Borneo, and in W Philippines (N Palawan and Calamian Is).

Descriptive notes. Head—body 67 mm, tail 123 mm, ear 13-8 mm, hindfoot 16-8 mm (measurements from type description). No specific weight data are available. The Sundaic Ranee Mouse is the smallest native rodent on Borneo. Original description by

Thomas in 1893 noted only size differences from Margaret's Ranee Mouse (H. margarettae), and descriptive notes for that species will thus apply also to the Sundaic Ranee Mouse. Tail of holotype measures 183% of head-body length. Musser and Carleton reported that Philippine specimens have paler underside on head and body, and paler hindfeet than those from Borneo, with additionalslight differences in dental traits.

Habitat. Natural habitat throughout range of the Sundaic Ranee Mouse is evergreen tropical lowland rainforest grading upward into montane forest at elevations above c.1000 m. Pagdanan Range, site of a recent capture on Palawan Island, supports a mosaic of old-growth, logged and regenerating lowland rainforest, and interspersed agricultural land. A specimen from Calauit Island, Palawan Province, Philippines, was captured by hand in a bamboo thicket.

Food and Feeding. No information.

Breeding. No information.

Activity patterns. Some terrestrial activity is indicated by J. Payne and coworkers’ report of a Haeromys (either present species or Margaret’s Ranee Mouse) captured in a pitfall trap in Sabah, Malaysia.

Movements, Home range and Social organization. No information.

Status and Conservation. Classified as Vulnerable on The IUCN Red List. There are very few records from anywhere within the species’ range. A capture was reported in 2003 in the Pagdanan Range, near northern end of Palawan Island. The most recent record from Borneo is probably the individual pit-trapped in Sabah, as reported by Payne and coworkers. In the four decades leading up to 2014, more than 30% of the original tropical rainforest cover of Borneo had been lost to habitat conversion, much of it to oil palm plantations. The range of the Sundaic Ranee Mouse is no doubt both strongly reduced and highly fragmented. The capture locality in East Kalimantan is now located in Kutai National Park, but less than 30% of original primary forest survives following decades of logging activity and destructive firing.

Bibliography. Chiozza (2016), Corbet & Hill (1992), Ellerman (1941), Esselstyn et al. (2004), Heaney et al. (1998), MacKinnon et al. (1994), Medway (1977), Musser & Carleton (1993, 2005), Musser & Newcomb (1983), Payne et al. (1985), Thomas (1893e, 19111), Widmann et al. (2004).