Family Pteropodidae
Old World fruit bats
(Also: flying foxes)

Members of Pteropodidae are known colloquially as the flying foxes, or Old World fruit bats. The family is composed of 41 genera and about 170 species. The most species-rich genus in the family is Pteropus with 59 species, many of which are island endemics. Body and wing size ranges from small (37 mm forearm length) to large (220 mm forearm length). The family boasts the largest bats in the world. Pteropus vampyrus individuals have a wingspan of up to 1.7 m. Pteropus giganteus individuals have a comparable wingspan but a greater mass, with males weighing between 1.3 and 1.6 kg. Pteropodids are strictly vegetarian, foraging for fruits, nectar, and pollen using their sight and a sensitive olfactory system. Bats of the genus Rousettus use tongue clicks as a crude form of echolocation while navigating in the dark. Some species are migratory, covering vast distances, while others have more moderate home ranges. Eidolon helvum individuals aggregate in numbers reaching the hundreds of thousands, yet many species roost with only a few conspecifics. Members of Pteropodidae service the ecosystems they inhabit by playing important roles as pollinators and seed dispersers. (Fenton, 2001; Koopman, 1994; Neuweiler, 2000; Nowak, 1999)

Pteropodidae has a tropical and subtropical distribution in the Old World (eastern hemisphere). Species are found as far north as the eastern Mediterranean, continuing along the southern coast of the Arabian Peninsula and across South Asia. Species are found as far south as South Africa, the islands of the Indian Ocean, and to the northern and western coasts of Australia. The longitudinal range reaches from the Atlantic coast of Africa to the islands of the western Pacific. Pteropodids are absent from northwest Africa, southwest Australia, a majority of the Palearctic region, and all of the Western Hemisphere. (Koopman, 1994; Mickleburgh, Hutson, and Racey, 1992; Nowak, 1994)

Pteropodids typically occur in primary or maturing secondary forests. A few species inhabit savannah habitats where they roost in bushes and low trees. Over half of the 41 genera are made up of species that roost in trees. Gregarious species roost on the open branches of large, canopy-emergent trees. Pteropodids that roost singly or in small groups can be found in dead palm leaves, aerial roots, and even arboreal termite nests. These bats also tend to have cryptic coloration and wrap themselves with their wings in order to resemble dead leaves. In one species, Cynopterus sphinx, individuals construct tents by chewing folds in palm leaves. Caves, cliff walls, mines, and the eaves of buildings also serve as roosting locations for species in 17 genera. Most cave-dwelling species are limited to the lit areas near the opening, while members of the genus Rousettus are able to navigate the darker regions using crude echolocation. (Mickleburgh, Hutson, and Racey, 1992; Nowak, 1994)

Flowering plants are essential to the diet of pteropodid species; therefore, flying foxes mostly use woodlands or orchards for food. Canopy emergent fruiting trees, such as fig and baobab trees, are frequently used as a food source. The flowers of baobab trees have a strong fragrance and are located on the crown of the tree, which makes them easily accessible to bats (a flower syndrome known as chiropterophily). Many pteropodid species are found in coastal areas and drink salt water in order to supplement nutrients lacking in their diet. (Fenton, 2001)

A few species are migratory. Eidolon helvum individuals gather in large numbers and migrate hundreds of kilometers northward with seasonal rains, only to return to southern Africa at the end of the rainy season. Pteropus scapulatus populations make major, and somewhat erratic movements within Australia, following the flowering periods of Eucalyptus trees. Many species of Pteropus roost on islands and make daily migrations to the mainland for foraging. Some species range from sea level to 2500 m, yet little is known about any significant elevational migrations. (Fenton, 2001; Mickleburgh, Hutson, and Racey, 1992; Nowak, 1994)

The family Pteropodidae is the most basal of all extant bat families. Chiropterans are thought to have shared a common ancestor with the order Dermoptera, or flying lemurs and colugos. The order Chiroptera used to be divided into two suborders: Megachiroptera (megabats), of which pteropodids were the sole members, and Microchiroptera (microbats), which was made up of all other bats. Recent phylogenetic studies have grouped several microbat families with Pteropodidae based on shared genetic traits. Megadermatidae, Rhinolophidae, Rhinopomatidae, Hipposideridae, and Craseonycteridae are now classified with Pteropodidae in the group Yinpterochiroptera; all other microbat families are contained within the group Yangochiroptera. (Altringham, 1996; Teeling et al., 2005; Wilson and Reeder, 2005)

Pteropodidae is further divided into two subfamilies. The frugivorous flying foxes make up the subfamily Pteropodinae, which contains three tribes: 1) Harpyionycterini- one species confined to the Phillipine Islands and Celebes 2) Epomorphorini- known from sub-Saharan Africa, and 3) Pteropodini, which shares the same distribution as the family. The nectarivorous flying foxes, characterized by their long, complex tongues and reduced teeth size, comprise the subfamily Pteropodidae. Designations of subfamilies based on feeding morphology have been largely criticized due to evidence that nectarivory evolved several times within pteropodids. Recent molecular work finds that pteropdid clades more closely reflect geography, with bats endemic to Africa nesting closely to one another on a phylogenetic tree, regardless of their adaptations to diet. (Koopman, 1994; Vaughn, Ryan, and Czaplewski, 2000; Wilson and Reeder, 2005)

Researchers once suggested that flying foxes do not share a common ancestor with other bats because of their significant differences in morphology and the inability of megabats to echolocate via laryngeal echolocation. Due to some similarities in neural structure, dentition, and penis morphology, Pteropodidae were thought to have descended from an ancestor shared with Dermoptera, Scandentia, and Primates, whereas other bat groups were said to have evolved from small insectivores. Based on this, it was concluded that the evolution of flight must have developed twice, independently, in the two groups. Recent molecular data, as well as more complete morphological databases, refute this theory and provide ample evidence for monophyly of Chiroptera. (Mickleburgh, Hutson, and Racey, 1992; Neuweiler, 2000; Teeling et al., 2005)

The head and body length of pteropodids varies from 50 mm to 406 mm. Despite size, many characteristics are shared among genera. A relatively long rostrum (pronounced in nectarivores), large eyes, and simple external ears give members of this family a dog or fox-like appearance (hence “flying fox”). The genera Nyctimene and Paranyctimene are exceptions in that they contain tubular nostrils that project from the upper surface of the snout. On the skull, postorbital processes are present over the orbital region. The palatine extends posterior to nearly cover the presphenoid. No more than two upper and two lower incisors are present in adults, otherwise cheek and canine dentition varies between species. The tongue is highly protrusible in nectar feeding bats and often complex with terminal papillae. (Myers, 2001; Neuweiler, 2000; Nowak, 1999)

The chest is robust, comprised of the down-thrusting pectoralis and serratus muscles. The articulating regions of the humerus never come into contact with the scapula, which differs from a locking mechanism that occurs in the shoulder joint of other bat groups. The second digit is relatively independent from the third digit and contains a vestigial claw that adorns the leading edge of the wing. (Altringham, 1996; Neuweiler, 2000)

Modifications for hanging include a relocation of the hip socket. The acetabulum is shifted upward and dorsally, and articulates with a large headed femur for a wider range of motion. In contrast to most other mammal orders, the legs cannot be positioned in a straight line under the body. In conjunction with large claws on their feet, pteropodids use a tendon-ratchet system that allows them to hang without prolonged muscular contraction. The legs manipulate a primitive uropatagium during flight. Aside from Notopteris, most species are tailless or with just a spicule of a tail. (Neuweiler, 2000)

Several species of Pteropodidae demonstrate sexual dimorphism. Males of Hypsignathus monstrosus have rather outlandish facial features, while females have the conservative fox-like look. Males of the genus Epomops have distinctive white patches in association with a glandular membrane on their shoulders, whereas females do not. Considering the whole family, males are generally larger than females. The penis of all pteropodids is a pendant and freely movable organ, resembling that of Primates. Juveniles are typically naked or have a velvety coat that is darker than adult pelage. (Neuweiler, 2000; Nowak, 1999)

Pteropodids have been known to live at least 30 years, both in captivity and in the wild. (Nowak, 1999)

Pteropodids are different from all other chiropteran in that, with the exception of Rousettus species, they do not echolocate. Pteropodids rely instead on vision and olfaction to perceive their world. Pteropodids can functionally be divided into two groups based on size. Smaller pteropodids such as Micropteropus pusilla, Epomops buttikorteri, and Epomophorus wahlbergi tend to have shorter, deeper wings which allow for more maneuverable flight under the canopy. Larger pteropodids such as Eidolon, Pteropus, and Acerodon species have longer, narrower wings which allow for efficient long distant flight. Pteropodid species display varying degrees of coloniality. This range is broad, from solitary species to those that roost in groups of up to 200,000 individuals. Roost size may also vary seasonally within a species, possibly due to a depletion of local food sources. Some species commonly roost in mixed groups with other species. Roost selection by pteropodids is poorly understood. Pteropodids roost in a wide range of habitats, from cultivated kapok plantations to rainforests and mangroves. Some species are associated with particular types of plants. Pteropodids can show long term fidelity to roost sites when the sites are undisturbed. Some species of Pteropus in Australia have been recorded using the same roost for over 80 years. (Kunz and Fenton, 2003; Mickleburgh, Hutson, and Racey, 1992)

Pteropodids rely heavily on vision and olfaction when navigating and foraging. Intraspecific communication is often vocal. In some species, such as Pteropus poliocephalus, vocal signaling may be associated with specific motor activities which enhance the meaning of the vocal signal. In species such as Eidolon helvum, sexually dimorphic sebaceous glands which are larger in males may provide olfactory behavioral cues. (Mainoya and Howell, 1979; Van Parijs and Corkeron, 2002)

Pteropodids are frugivorous and nectarivorous. Some species also eat flowers of the plants they visit. Foraging habits are not well documented, though many species of the genus Pteropus rely heavily on figs. Many species rely on broad array of resources, though there may be a functional dichotomy between large species that rely heavily on canopy resources and smaller species that can use understory resources. Some larger species can use the claws on their thumbs and second digits to climb into the understory and seek out fruit that is hidden or inaccessible by flight. (Kunz and Fenton, 2003; Mickleburgh, Hutson, and Racey, 1992)

Birds of prey and carnivorous mammals, as well as snakes and large lizards may prey on pteropodids. Pteropodids tend to have fewer predators on islands. However, there have been several cases of introductions of non-native, arboreal snakes which have decimated pteropodid populations. (Mickleburgh, Hutson, and Racey, 1992)

Pteropodids provide important pollination and seed dispersal services to a wide range of plants. On islands in the south Pacific, pteropodids are the principle pollinators and dispersers of plants. Many plants have adaptations specifically for seed dispersal and pollination by bats, such as fruiting or flowering at the ends of branches and at bat accessible locations in the canopy. Eidolon dupreanum has been shown to likely be the sole pollinator of the baobab tree Adansonia suarezensis in Madagascar. (Cox et al., 2005; Kunz and Fenton, 2003; Mickleburgh, Hutson, and Racey, 1992; Racey et al., 2006)

Many crop species are attractive food sources for pteropodids. Because cultivars are often developed from wild species, these commercial crops have the same characteristics that wild plants evolved to attract bats to their fruit. Fruit growers have experimented with visual, audio, and olfactory deterrents as well as electric wire to keep pteropodids from eating their crops. Pteropodids may also be dispersers of invasive plant species, as they consume crops introduced for cultivation and may disperse the seeds into natural habitat. Pteropodids have been indicated as reservoirs for a variety of viruses such as Ebola and other viruses in the family Paramyxoviridae. Hendra virus, Menangle virus, and Nipah virus have all been linked to pteropodids. (Mickleburgh, Hutson, and Racey, 1992)

Larger species of pteropodids are hunted for their meat. Both subsistence and commercial hunting of Pteropus species have been reported. Consumer demand for Pteropus species on the island of Guam has been so great that it has resulted in the extinction of at least one species in the Pacific region. Flying foxes are also important in the dispersal and pollination of economically important plants. They attract tourists in some areas and produce accumulations of guano that can be used as fertilizer. (Mickleburgh, Hutson, and Racey, 1992)

Many factors threaten pteropodids throughout their range. Human activities have decimated populations of certain species directly through hunting or indirectly through habitat destruction. In Asia and Australia, deforestation is the most important contributor to pteropodid population decline. Some species are vulnerable to typhoons and hurricanes which may destroy roosting habitat on islands. The IUCN Red List of Threatened Species lists 5 species as recently extinct, 10 species as critically endangered, 19 species as endangered, 15 species as near threatened, and 39 species as vulnerable, suggesting that nearly half of all pteropodid species face significant threats to population viability. (IUCN 2008, 2008; Kunz and Fenton, 2003)