There are over 4,000 mammal species in the world and almost one in four of them is a bat. All bats belong to the order Chiroptera. This order includes two major sub-orders, the Microchiroptera, or true bats, currently comprising 782 species, and the Megachiroptera, comprising 175 species (Neuweiler, 2000).

The Microchiroptera, without exception, possess a highly developed echolocation system (Neuweiler, 2000). Thanks to a combination of echolocation and flying skills most species have become skilful nocturnal hunters and the majority are insect feeders, although other food sources include fish, amphibians, small mammals (including bats), blood, fruit and flowers (e.g. Altringham, 1996). Microchiropteran bats are found in all areas of the world apart from the Arctic and Antarctica and some isolated oceanic islands (Nowak & Walker, 1994).

The Megachiroptera (consisting of a single family, the Pteropodidae or Old World fruit bats or ‘flying-foxes’) are found throughout the Old World tropics and range from Africa, the eastern Mediterranean, Madagascar and the Indian Ocean islands in the west, across mainland southern Asia, throughout the islands of the western Pacific from the Ryukyu Archipelago and Ogasawara-Shato in the north, to coastal eastern Australia, New Caledonia and the Loyalty Islands in the south, and east to Fiji, Tonga, Samoa and the Cook Islands (Figure 1) (Mickleburgh et al., 1992). They are especially diverse in south-eastern Asia and Indo-Australia (Hall & Richards, 2000; Mickleburgh et al., 1992).

Figure 1. World distribution of the Megachiroptera. (from Hill & Smith, 1984)

All megachiropterans are nocturnal with the notable exception of Pteropus samoensis (e.g. Brooke, 2001). Echolocation is, with a few exceptions (i.e. some Rousettus and perhaps Epomophorus species) unknown in the Megachiroptera, and members of the group largely depend on their large eyes specialized for night vision. Many species are sexually dimorphic. Differences between the sexes include the larger body size of males (most species), males having larger canines (many species), and males with conspicuous skin glands (a few species) (Hill & Smith, 1984; Nowak & Walker, 1994). Sexual differences are extreme in one species, H. monstrosus, in which males have very large pharangeal sacs that extend into the chest and a huge larynx (used in producing a loud "honk" that is part of a sexual display) (e.g. Bradbury, 1977).

All pteropodids are frugivorous or nectarivorous (Mickleburgh et al., 1992). Pteropodids are important pollinators and dispersers of tropical trees, many of which are adapted to attract bats and make their pollination/dispersal activities more efficient (Marshall, 1985). In some instances pteropodids may also cause significant damage to orchards. The larger species are sometimes hunted for their meat.

Megachiroptera of the genus Pteropus are the largest bats in the world, ranging in adult weight from 250 to 1000 g and have a wingspan of up to 1.7 metres. The Pteropus genus has currently 57 recognised species (Mickleburgh et al., 1992). Pteropus is primarily an island taxon, with 55 species having some or all of their distribution on islands. In this genus levels of endemism are extremely high, with 35 species confined to single islands or small island groups. Only nine species are found in continental areas (five in Asia and four in Australia), and only two (P. lylei and P. poliocephalus) are restricted to continents (Mickleburgh et al., 1992).

All Pteropus species are exclusively phytophagus, feeding on floral resources (primarily nectar and pollen), fruits, leaves, bark and seeds (Marshall, 1985). Diet trees for most species comprise canopy and sub-canopy rainforest species, although Pteropus also feed in mangrove, swamp and temperate forest vegetation (Marshall, 1983).

The distributional characteristic and dietary limitations make Pteropus populations vulnerable to agricultural clearing of forests, harvesting of animals for human consumption, and programs for culling animals on crops (Wilson & Graham, 1992 and references therein). As a result, the current conservation status of many Pteropus species is not secure.

The priority grading for species action assigned by the International Union for the Conservation of Nature and Natural Resources (IUCN) (Baillie & Groombridge, 1996) assigns species to categories according to their danger of extinction. In 2004 (IUCN, 2004), five species were classed as extinct (EX), seven species were classed as critically endangered (CR), three species were classed as endangered (EN), sixteen species were classed as vulnerable (VU), three species were classed as lower risk (LR), and of two species not enough was known to determine their conservation status (DD). The remaining species were classed as Not Evaluated (NE) because they have not been assessed against these criteria.

Pteropus species have a slow life cycle characterized by low fecundity and a long life-span (e.g. McIlwee & Martin, 2002). Species that possess slow life cycles are likely to contain a higher proportion of old, experienced individuals than short-lived species, providing scope for intricate forms of social organisation (e.g. Calder, 1983).