Rousettus spinalatus, Bergmans & Hill, 1980

Don E. Wilson & Russell A. Mittermeier, 2019, Pteropodidae, Handbook of the Mammals of the World – Volume 9 Bats, Barcelona: Lynx Edicions, pp. 16-162 : 85-86

42.

Bare-backed Rousette

Rousettus spinalatus

French: Roussette a dos nu / German: Nacktrlicken-Flughund / Spanish: Rosetus de espalda desnuda

Taxonomy. Rousettus spinalatus Bergmans & Hill, 1980 ,

“northern Sumatra (either in or near Medan, or in or near Prapat),” Indonesia.

This species is monotypic.

Distribution. N Sumatra and N Borneo (Sabah, Brunei, Sarawak, and North Kalimantan).

Descriptive notes. Head-body 105 mm (type specimen), tail 9-18 mm, ear 15- 22.5 mm, hindfoot 15:- 5-19 mm, forearm 80-6-89- 3 mm; weight 66- 4-94 g. Males are larger than females. Wings of the Barebacked Rousette originate at dorsal midline, thereby giving appearance of a bare back. Muzzle is conical, with sparse fur of short very dark brown hairs. Center of chin and throat is almost naked. There are 15 small warts, each with one long vibrissa, on either side of head between nostrils, eyes, and upperlip; 10-15 warts also occur on either side of chin on lower lip and aboutsix warts at either side of the area under eye behind mouth corner. Nostrils are separated by vertical clef that protrudes slightly and is directed forward and outward. Chin pad is widely V-shaped, with shallow groove in median plane and notched at its proximal point and with short and narrow offshoot at each side along lowerlip. Lips are thick, each with single row of very small papillae on posterior one-half of inner margin. Ears are moderately long, rather broad at bases and gradually narrowing to obtuse point; margins are thickened at bases. Antitragal lobe is thick and quite distinct. Ears are naked, except for lower posterior part of outer surfaces; skin of conch is dark brown. Nape has very few, long dark brown hairs. Dorsum between shoulders is almost naked in some specimens. Mantle continues along upper arms in narrow stretch to a point c. 21 mm from elbow. Male’s necks have yellowish orange tufts on both sides. Chest and belly have relatively dense but rather short drab fur. Dorsum under plagiopatagium and part of adjoining sides of body are covered with fairly long (5-8 mm), bicolored hairs. Fur on rest of body is generally pale brownish gray. Wing is relatively short and broad. From a point dorsal to axilla, plagiopatagium extends following distal margin of scapula toward spinalline, which is reached at level of caudal point of scapula, and following spinal line until proximal part of leg and extending up to inside of proximal end offirst phalanx of first toe. Wings are joined for ¢. 10 mm above back before they diverge. Dorsal side of uropatagium, tibia, and toes have sparsely scattered hairs. Dorsally, uropatagium appears as an extension of plagiopatagium because it is also inserted along dorsal side of proximal part of leg, along same commissure as plagiopatagium, further along inner side of tibia, and along spinal line, to halfway on external tail. Wings and tail membrane are dark brown; propatagium, parts of plagiopatagium (near forearm and body), and uropatagium except for caudal zone are more translucent than rest of wing membranes. Ventral sides of legs are naked. Skull is similar to that of Geoffroy’s Rousette ( R. amplexicaudatus ), differing mainly in dentition. Premaxillae are slender, in contact but not co-ossified anteriorly. Braincase is moderately deflected. Temporal ridges are separate anteriorly, uniting at c. 5 mm from supraoccipital ridge. Interorbital constriction is similar in width to postorbital constriction; braincase is highly domed. Zygomatic arches are slender. Mandible is slender and relatively broad anteriorly, with relatively high coronoid process. Palatal ridges have a 3 + 4 + 1 pattern. Upper incisors are small, I? is somewhat larger than I' and curved posteriorly and inwardly, and I? is separated from C' by narrow diastema (c. 1 mm). P' is small, next premolar (P°) is short and narrow, and P* is low. M! is low and rectangular, and M? is low, more or less rectangular, with anterior width greatest. P| is low, squarish, and rather small; P, is rather high, narrow, and elongated; and P, is low and rounded anteriorly. M,is low, long, and generally rectangular; M,is similar to M, but shorter, lower, and wider anteriorly; and M,is smaller and lower.

Habitat. Tropical lowland rainforests from sea level to elevations of ¢. 300 m.

Food and Feeding. The Bare-backed Rousette is thought to feed on nectar and fruits. There are anecdotal claims that it damages and eats swiftlet nests.

Breeding. Seven female Bare-backed Rousettes were pregnant in August 1984 in Sabah. Similarly, five males collected in the same occasion had greatly enlarged testes. Sabah is nearly aseasonal, with abundant rainfall every month of the year.

Activity patterns. Bare-backed Rousettes are nocturnal and presumably emerge from caves after sunset and return before sunrise. They roost in dark caves; individuals in a colony produced click calls similar to those of Geoffroy’s Rousette, suggesting ability to echolocate.

Movements, Home range and Social organization. Colonies of ¢.300 Bare-backed Rousettes have been recorded, and they share roost caves with Geoffroy’s Rousettes.

Status and Conservation. Classified as Vulnerable on The IUCN Red List. The Barebacked Rousette is considered rare. Populations are estimated to have declined by more than 30% over a 15-year period due to habitat loss; this decline is predicted to continue in the future, but no conservation plans are in place.

Bibliography. Bergmans & Hill (1980), Francis (1989), Francis, Hutson, Sinaga & Kingston (2008), Payne et al. (1985), Rookmaaker & Bergmans (1981).

Figures

32. Zenker’s Fruit Bat (Scotonycteris zenkeri), 33. Hayman’s Fruit Bat (Scotonycteris occidentalis), 34. Bergmans’s Fruit Bat (Scotonycteris bergmansi), 35. Short-palated Fruit Bat (Casinycteris argynnas), 36. Pohle’s Fruit Bat (Casinycteris ophiodon), 37. Campo-Ma’an Fruit Bat (Casinycteris campomaanensis), 38. Lesser Dawn Bat (Eonycteris spelaea), 39. Greater Dawn Bat (Eonycteris major), 40. Philippine Dawn Bat (Eonycteris robusta), 41. Geoffroy’s Rousette (Rousettus amplexicaudatus), 42. Bare-backed Rousette (Rousettus spinalatus), 43. Leschenault’s Rousette (Rousettus leschenaultin), 44. Linduan Rousette (Rousettus linduensis), 45. Sulawesi Rousette (Rousettus celebensis), 46. Egyptian Rousette (Rousettus aegyptiacus), 47. Malagasy Rousette (Rousettus madagascariensis), 48. Comoro Rousette (Rousettus obliviosus), 49. Long-haired Fruit Bat (Stenonycteris lanosus)

Distribution. N Sumatra and N Borneo (Sabah, Brunei , Sarawak , and North Kalimantan).