Bulmer’s Fruit Bat (Aproteles bulmerae)

Bulmer’s fruit bat (Aproteles bulmerae) is a large megabat in the family Pteropodidae, order Chiroptera. Endemic to the low‑land tropical rainforests of Papua New Guinea’s Bulmer region in the Sepik River basin, it is one of the world’s most range‑restricted bats, known from fewer than ten specimens collected in the 1970s and a handful of unconfirmed sightings since. Adults have a fox‑like face, dark brown to black fur, and a wingspan that can exceed 1.2 m (4 ft). The species is nocturnal, roosting in small colonies of up to a dozen individuals in the canopy of mature forest trees. Its diet consists almost entirely of ripe figs and other rainforest fruits, which it extracts with a long tongue while in flight. The International Union for Conservation of Nature (IUCN) lists A. bulmerae as Critically Endangered (Possibly Extinct) because no confirmed individuals have been recorded for more than two decades and its habitat has been heavily logged. Conservation efforts are hampered by the bat’s cryptic behaviour, the inaccessibility of its remaining forest patches, and limited local awareness. Protecting the remaining primary forest and conducting targeted acoustic surveys are considered the most urgent actions to determine whether any viable population persists.

Bulmer’s fruit bat lives in small, loosely structured colonies that occupy the upper canopy of primary rainforest. Individuals are highly social, engaging in mutual grooming, wing‑clasping, and low‑frequency vocalizations that maintain group cohesion during the night. The species is strictly nocturnal; it emerges at dusk to forage and returns to its roost before sunrise. Home ranges are believed to extend 5–10 km from the roost, following the seasonal fruiting of fig trees. Males defend temporary foraging territories but do not maintain permanent harems; instead, they compete for access to receptive females during the brief breeding window. Communication relies on a repertoire of clicks, squeaks, and a distinctive low‑pitched “purr” that can travel several hundred metres through dense foliage. Because the bats are reluctant to travel over open gaps, fragmented forest creates barriers that limit dispersal and increase the risk of local extirpation.

Bulmer’s fruit bat is a specialist frugivore, relying almost exclusively on the fruit of large canopy figs (Ficus spp.) and a limited selection of other rainforest fruits such as mango‑like Myristica and wild bananas (Musa spp.). An adult consumes approximately 150–200 g of fruit per night, which provides the high carbohydrate and water intake needed for sustained flight. The bat employs a “hover‑and‑pluck” feeding strategy, using its elongated tongue and sharp incisors to bite into soft pulp while hovering in front of the fruit. Occasionally, it supplements its diet with nectar and pollen from flowering trees, which contributes protein and essential minerals. By discarding seeds beneath the roost and feeding sites, the species acts as an important seed disperser, facilitating forest regeneration across its limited range.

Sexual maturity in Bulmer’s fruit bat is reached at about two years for both sexes, although females may breed slightly earlier in years of abundant fruit. Breeding is synchronized with the peak fruiting period of the dominant fig species, typically occurring between November and January. After a gestation of roughly 5.5 months, females give birth to a single pup, which is among the largest newborns of any bat, weighing about 10 % of the mother’s body mass. Newborns are altricial, blind and hairless, and cling to the mother’s ventral fur for the first two weeks. The mother nurses the pup nightly, providing a milk rich in lipids that supports rapid growth; weaning occurs at 8–10 weeks when the juvenile begins to accompany the mother on short foraging trips. Juveniles attain full flight capability by three months and reach adult size by one year, after which they integrate into the colony’s social network.

The IUCN classifies Bulmer’s fruit bat as Critically Endangered (Possibly Extinct) due to an estimated population of fewer than 50 mature individuals, if any remain. The primary threat is habitat loss: commercial logging and slash‑and‑burn agriculture have removed more than 70 % of the original low‑land forest in the Bulmer region since the 1970s. Hunting pressure, although historically low, has increased as local communities turn to bushmeat for protein, and the bat’s large size makes it a desirable target. The species’ extreme range restriction amplifies the impact of stochastic events such as cyclones and disease outbreaks. Climate change may further alter fruiting phenology, reducing food availability during the breeding season. Conservation actions proposed include establishing a protected area encompassing the remaining primary forest, implementing community‑based monitoring, and conducting intensive acoustic and mist‑net surveys to confirm the species’ presence.

• Bulmer’s fruit bat was first discovered in 1975 during a short‑term biological survey in Papua New Guinea.
• It has one of the smallest known geographic ranges of any mammal, confined to less than 100 km² of lowland forest.
• The species’ wingspan can exceed 1.2 m, making it one of the largest fruit bats in the world.
• Its large, fox‑like face and bright eyes give it a distinctive appearance that inspired the common name “Bulmer’s flying fox.”
• Despite its rarity, the bat plays a crucial role in seed dispersal for several fig species, helping maintain forest diversity.