Dobsonia moluccensis (Quoy & Gaimard, 1830)

Don E. Wilson & Russell A. Mittermeier, 2019, Pteropodidae, Handbook of the Mammals of the World – Volume 9 Bats, Barcelona: Lynx Edicions, pp. 16-162 : 108-109

83.

Moluccan Naked-backed Fruit Bat

Dobsonia moluccensis

French: Roussette des Molugues / German: Molukken-Nacktrickenflughund / Spanish: Dobsonia de las Molucas

Other common names: Bare-backed Fruit Bat / New Guinea Naked-backed Fruit Bat (magna)

Taxonomy. Hypoderma moluccensis [sic] Quoy & Gaimard, 1830 ,

Amboina Island, Maluku (Islands), Indonesia.

There is disagreement among authorities as to whether the two subspecies here are distinct species. Most authorities since K. Andersen in 1912 treated the two taxa as subspecies of moluccensis ; however, W. Bergmans and S. Sarbini in 1985 and T. F. Flannery in 1995 regarded magna and moluccensis as distinct species. A modern treatment using DNA was attempted by D. G. P. Byrnes in 2005, but she had limited number specimens and did not have adequate sampling of the distribution to untangle the confusion. Thus, taxonomy of what might be a species complex still requires additional molecular analysis. Two subspecies recognized.

Subspecies and Distribution.

D.m.moluccensisQuoy&Gaimard,1830—Moluccas(Bacan,Buru,Ambon,andSeramIs,alsoonBanda,Kai,andAruIsgroups).

D. m. magna Thomas, 1905 — New Guinea (including Waigeo, Batanta, Salawati, and Misool in Raja Ampat Is, Yapen, Kariru, Karkar, and Sideia Is) and N Australia (N Queensland).

Descriptive notes. Head-body 185-210 mm, tail 25-30 mm, ear 27-35 mm, forearm 120-146 mm; weight 490-500 g for subspecies moluccensis ; head—-body 191-254 mm, tail 21-42 mm, ear 28-41 mm, hindfoot 30-47 mm, forearm 136-162 mm; weight 325— 600 g for subspecies magna. There is sexual dimorphism in body weight within magna, with males up to 600 g but females only up to a maximum of 525 g. Sample sizes are inadequate to know if sexual dimorphism in nominotypical moluccensis occurs. The Moluccan Naked-backed Fruit Bat is the largest species of Dobsonia . Wings attach along midline of back and cover dorsal fur beneath. Fur is uniformly medium brown to gray-brown on face and dorsum. Ventral fur is pale gray-brown. Flight membranes are black. Ears are long and narrow, rising well above crown of head. Inner surfaces of pinna are well ribbed along basal one-half. Shortly tubular nostrils diverge and extend slightly beyond snout. Eyes are large and produce “eye shine” when light is focused on them in a dark cave; irises are brown. Claws of feet and thumbs are pale tan or whitish. Index claw (second digit of wing) is absent. There are two pairs of musk-producing sebaceous glands, one pair that runs from base of ears down and forward toward corners of mouth and another thatlies ventro-laterally on shoulders near anteriorjunction of wing patagia to the body. These glands are most prominent in adult males during breeding season but observable on females. There is a well-marked anterointernal basal ledge on upper and lower third premolars and a posterior basal ledge on second upper and lower premolars and third upper premolar. There is a median-surface ridge in M' and M,, often present in P* and M. Anterointernal corner of Mis not differentiated as a distinct cusp or ledge. Pineal gland is large compared with other mammals of its body weight, which fluctuates in size and control of hormonal activity associated with seasonal cycles of reproduction.

Habitat. Commonly coastal lowlands high into montane habitats in primary and secondary tropical moist forests, and highly disturbed areas such as village gardens and fruit plantations from sea level up to elevations of ¢. 2700 m. The Moluccan Nakedbacked Fruit Bat is rare in dry woodlands and savannas. It has a larger distribution and occupies more varied habitats and elevational range than any other species of Dobsonia (but it might be a species complex, and if so, distributions of individual taxa not yet differentiated and their preferred habitat would be different).

Food and Feeding. The Moluccan Naked-backed Fruit Bat is frugivorous. Important fruiting plants in diets include native species of Ficus (Moraceae) , Terminalia (Combretaceae) , Callophylum ( Calophyllaceae ), and Eucalyptus (Myrtaceae) and cultivated banana, papaya, and Pangium edule ( Achariaceae ). Because of the increased surface area, the odd attachment of wings is thought to improve ability to fly slowly by providing additional lift compared with other pteropodids and thus aids in search for fruit such as cauliflorousfigs in dense vegetation and to allow hovering before taking roost. Naked-backed wing surfaces possibly assists with takeoff carrying heavier fruits and to maneuver in places inaccessible to larger pteropodids. The Moluccan Naked-backed Fruit Bat sometimes lands on the ground for fallen fruit and has been caught in deadfall traps set for bandicoots ( Peramelidae ).

Breeding. Musk-producing sebaceous glands on face and shoulders are well developed in males but much less so in females. Glands hypertrophy during the breeding season, at which time they release musky, waxy substance possibly associated with mate selection. During breeding season in April-June in highlands of New Guinea, females develop perineal flesh folds that are of unknown significance. The Moluccan Naked-backed Fruit Bat has one young/litter and one litter/year. Females in Eastern Highlands Province, Papua New Guinea, give birth in a loosely synchronized season in August-November. Gestation lasts ¢.5 months. Young are weaned at c.4-5 months. During lactation, mothers will carry their young short distances to new roost perches but usually leave them at the roost when foraging. Males and females are believed to become sexually mature at c.2 years of age.

Activity patterns. Moluccan Naked-backed Fruit Bats are nocturnal. They emerge well after sunset in complete darkness. Wingbeat creates a “pok-pok” sound from air compressing and expressed from spaces under pockets of wing membranes over the back. Roosts are in limestone caves and recessed shaded walls ofsinkholes, under rock overhangs, and less commonly in tree hollows or tree crowns within thick foliage. They penetrate caves to the far reaches of dim light, apparently limited by dependence on visual orientation.

Movements, Home range and Social organization. Moluccan Naked-backed Fruit Bats are highly gregarious, but roosting groups vary from solitary individuals to groups of tens, hundreds, or thousands of individuals. They will cohabit caves with Beaufort’s Naked-backed Fruit Bat ( D. beauforti ). Group size in tree hollows and tree crowns including coconut trees are limited to small numbers. In Australia, colonies are relatively small, approaching a maximum of 100 individuals and have been found in caves, dark areas under large boulders, old mines, abandoned houses, and dense vegetation. It exhibits extremely high thermal conductances that can be 180% of that expected for a mammal of its body weight. Such exceptionally high thermal conductance is facilitated by naked-backed wing condition and likely assists in efficiently dumping heat in this largebodied species that roosts clumped together. Preference for roosting at interior limits of cool caves also facilitates heat dumping to cool air in cave interiors. Naked-backed wing morphology is related to its ability to fly with amazing maneuverability at low speeds, including its ability to hover and fly backward. As they search for a place to roost when approaching a cluster of roosting conspecifics, they are able to hover, repeatedly reverse direction, and then move forward slowly to land by swinging feet upward to grab onto rock. They also fold wings and dive up to 300 m to approach a particular cave entrance. If disturbed at the roost by a predator, they are highly vociferous; otherwise there are only occasional antagonistic with vocalizations coupled with wing boxing between individuals that attemptto displace each other from mates or favored roost positions. Potential predators include large pythons such as the amethystine python ( Morelia amethistina) that will enter caves to feed on bats. Physiological responses to environmental temperature variation of Moluccan Naked-backed Fruit Bats appear adaptive to cave dwelling and avoidance of predation. These responses include maintenance of constant high body temperature (mean = 36-8°C), high minimum thermal conduction (mean = 180% of mammalian mass-specific standard), and high basal metabolic rate (BMR, mean = 145% of mammalian standard). Maintenance of high body temperature and high BMR might facilitate rapid growth and care of young (including milk production) and ability to fly instantaneously in response to a predator. High minimal termal conductance (largely through highly vascularized naked-backed wings) facilitates heat loss for a largebodied bat that otherwise might overheat in crowded roosting clusters. Large colony size also might raise cave air temperatures, making excess body heat more difficult to unload. Large colonies of Moluccan Naked-backed Fruit Bats often have infestations of large fur-dwelling bat flies including Megastrebla parvior and M. gigantea. Terrestrial leeches often hang from cave ceilings and drop on Moluccan Naked-backed Fruit Bats.

Status and Conservation. Classified as Least Concern on The IUCN Red List (but excluding magna). The Moluccan Naked-backed Fruit Bat has a very large distribution and is perhaps the most abundant fruit bat in New Guinea, and there is no indication that the population is in decline. Informal protection by local landowners sometimes provides conservation of populations, such as at Omeru Village, Madang Province, Papua New Guinea, where local people offer an ecotourism experience to view a colony estimated to be 10,000 individuals on walls of a large sinkhole. Indigenous people hunt it for local consumption, but hunts often are restricted to provide for holiday feasts and special occasions by local custom. In some places, farmers and villagers consider it a pest for raiding fruit trees such as papaya. Villagers in New Guinea will set large fishing hooks inside fruit to snag raiding bats.

Bibliography. Andersen (1912b), Bergmans (1979b), Bergmans & Sarbini (1985), Bonaccorso (1998), Brass (1964), Byrnes (2005), Duncan et al. (1999), Dwyer (1975), Flannery (1995b), Hall (1983), Helgen (2007a), Koopman (1979, 1982b), Maa (1971), McNab & Bonaccorso (2001), Phillips (1968), Strahan (1995), Wilson, D.S. (1975).

Figures

73. Lesser Long-tongued Blossom Bat (Macroglossus minimus), 74. Greater Long-tongued Blossom Bat (Macroglossus sobrinus), 75. Southern Blossom Bat (Syconycteris australis), 76. Halmaheran Blossom Bat (Syconycteris carolinae), 77. Moss-forest Blossom Bat (Syconycteris hobbit), 78. Manado Fruit Bat (Boneia bidens), 79. Sulawesi Harpy Fruit Bat (Harpyionycteris celebensis), 80. Philippine Harpy Fruit Bat (Harpyionycteris whitehead), 81. Bulmer’s Fruit Bat (Aproteles bulmerae), 82. Lesser Naked-backed Fruit Bat (Dobsonia minor), 83. Moluccan Naked-backed Fruit Bat (Dobsonia moluccensis), 84. Western Naked-backed Fruit Bat (Dobsonia peronu), 86. Panniet Naked-backed Fruit Bat (Dobsonia pannietensis), 87. Philippine Naked-backed Fruit Bat (Dobsonia chapmani), 88. Biak Naked-backed Fruit Bat (Dobsonia emersa), 89. Sulawesi Naked-backed Fruit Bat (Dobsonia exoleta), 90. Greenish Naked-backed Fruit Bat (Dobsonia viridis), 91. Beaufort’s Naked-backed Fruit Bat (Dobsonia beauforti), 92. Halmahera Naked-backed Fruit Bat (Dobsonia crenulata), 93. Solomons Naked-backed Fruit Bat (Dobsonia inermis), 94. New Britain Naked-backed Fruit Bat (Dobsonia praedatrix)

Subspecies and Distribution. D.m.moluccensisQuoy&Gaimard,1830—Moluccas(Bacan,Buru,Ambon,andSeramIs,alsoonBanda,Kai,andAruIsgroups). D. m. magna Thomas, 1905 — New Guinea (including Waigeo, Batanta, Salawati, and Misool in Raja Ampat Is, Yapen, Kariru, Karkar, and Sideia Is) and N Australia (N Queensland).