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Fruit & Nectar Bat Biology

The Megachiroptera are the old world fruit bats or flying foxes. This suborder comprises only one family, the Pteropodidae, which contains 45 genera and more than 170 species. Old World fruit bats differ from the microbats (Microchiroptera) in a number of key features:

• Old world fruit bats are generally larger than the microbats, with wing spans of up to 1.8m in some species (Pteropus vampyrus can weigh up to 1.5kg).
• The old world fruit bats, as the name suggests, all eat fruit, flowers or their products. They possess long tongues and snouts for reaching into flowers, and have flattened molars, pronounced canines and powerful jaws for piercing the tough rinds of fruits. Their dentition is designed for a soft diet. The microbats are typically insectivorous (although a few have adopted a diverse range of diets that include blood, fish and nectar) with flattened snouts and sharp, W-shaped cusped teeth characteristic of their insectivorous ancestry.
• Old world fruit bats have large, well developed eyes and primarily use sight to orient themselves, whereas microbats use highly developed systems of echo-location and have small eyes.
• Microbats are found all over the world but the Megachiroptera are only found in the Old World tropics.
• The ears of the Pteropodidae are rather simple and oval in shape when compared to the ears of the microbats, which are very complex organs adapted for echo-location. Microbats also possess a tragus (a small structure inside the ear), which the Pteropodidae lack (Altringham, 1996).

Pteropus

This website is concerned primarily with fruit bats of the genus Pteropus. Pteropus bats do not occur in continental Africa, Europe or the Americas but are widespread throughout Asia, from Pakistan and India, China and South East Asia through to Australasia and the Pacific islands (Nowak, 1994). They are found on the pacific islands, ranging as far as Fiji and Samoa but not as far as Hawaii. In fact, relatively few species live on the Asiatic mainland and most (96.5 % of Pteropus species) live on pacific islands (Mickleburgh et al., 1992). Pteropus is the largest and best known genus of old world fruit bats (58 species) and many of its species are under threat of extinction. The genus contains the majority of the Pteropodidae, mostly the larger ones, but even the smallest have a wingspan of around 80 cm. They are characterized by a contrasting mantle, which is usually yellowish or tawny, while the body is usually dark brown, greyish or black (Mickleburgh et al., 1992).

Tropical Forests such as mangroves and rain forest are the most important habitats for fruit bats. Most species roost communally in large groups on exposed branches of large emergent trees (those that rise above the canopy) although some roost singly or in small groups, and some form colonies in caves or rock shelters (Churchill, 1998; Pierson & Rainey, 1992). Some Indian species prefer thick foliage (Advani, 1982) to shade them from the sun, as do species in Australia and New Caledonia (Mickleburgh, 1992). Normally flocks will favour a particular roosting tree that they may occupy for years, however, human disturbance and increased hunting pressure can cause colonies to relocate to new roosting sites in sub-optimal habitat (Falanruw, 1988).

Advantages to roosting in large groups include:

• Thermal advantages: Heterothermy. Although it inhibits rapid escape, it may also reduce smell.
• Dense foliage protects from weather and the sun.
• More eyes increases vigilance - reduces time spent scanning for predators per capita, leaving more time for feeding and mating, etc.
• Foliage hides them from predators. They are camouflaged by their fur patterns and wrap their wings around themselves to resemble dead leaves (Churchill, 1998).

Foraging

Fruit Bats are mainly active in the evening and at night, when the larger species often fly up to 15 km from their roosting sites to feed (Fujita & Tuttle, 1991). They can bite fruit while hovering and sometimes carry a piece in their mouth and find a branch where they hang upside down by one foot holding the fruit in the other while they eat it. Fruit is chewed up and the pulp pressed against the ridged palate of the mouth and the juice sucked out. The dry matter, containing seeds and pulp, is then spat out in the form of pellets (Funakoshi, et al., 1993). The digestive tract is simple and food takes on average only half an hour to pass through the gut (Mickleburgh et al., 1992). Pteropus bats have also been observed eating insects, which are thought to supplement the meagre protein intake they recieve from plant matter. This is seen in captive fruit bats (P. rodricensis), which will eat meal worms, crickets and other insects when presented with them (Pope, 1998). In the wild this has been seen in P. dasymallus, which takes up to eight species of insects in its diet (Funakoshi et al, 1993)

Reproduction

Males and females look the same and there are usually no secondary sexual characteristics. Females give birth once a year and occasionally have twins. The young are not themselves ready to reproduce until they are 1.5-2 years old, which is a particularly slow reproductive rate for a mammal of their size (Falanruw, 1988). For illustration, compare the reproductive rate of a pair of pteropids with a pair of rats (genus Rattus). After one year, with zero mortality, there will be three, at the most four, bats and about 4,000 rats (Pierson & Rainey, 1992). This is a crucial problem for their conservation because their reproductive rate is not high enough to withstand with the high predation pressure exerted by man in many parts of the world (Pierson & Rainey, 1992).

Evolution

The Two chiropteran suborders probably diverged around the late Cretaceous or early Palaeocene, and the Pteropodinae probably arose in the Australo-Pacific or south-east Asia around the Early Miocene (Kirsch et al., 1995). The closest relatives to the Pteropus genus are Acerodon, which are a very similar size and morphology. Unfortunately, bat bones are delicate and so do not fossilise well, so the fossil record is scrappy and many of the important early stages of bat evolution are missing. There are two rival theories concerning the evolution of the Megachiroptera and Microchiroptera. One theory suggests that the two suborders are the result of convergent evolution and that flight evolved separately in both lineages. This hypothesis (Smith and Madkaur, 1980; Pettigrew, 1996) suggests that the Megachiroptera probably developed from an early branch of the primate lineage because they share with them a number of unique features in the arrangement of the neural pathways that are not shared by the Microchiroptera or any other mammals. Many clues in the fossil record and anatomical differences in the two suborders suggest the two are evolutionarily distant, and the link between the Megachiropteraand the primates is further strengthened by modern molecular analysis of the amino acid sequence of the haemoglobins (Altringham, 1996). The penis resembles that of some primates and the females possess a single pair of mammae on the chest (Nowak, 1991). The idea that true flight might have developed twice in mammals is not too far fetched when one considers that it has evolved many times in the vertebrates already. However, compelling genetic evidence to the contrary is offered by Mindell and co-workers (1991) who propose that the similarities between the primates and megachiropterans are due to convergent evolution. Interestingly, Kirsch et al. (1995), using the modern DNA hybridization technique, also concluded that and the Megachiroptera are in fact closer to the Microchiroptera than to the primates.

Information on this page was compiled and authored by Oliver Thatcher and is currently being updated.

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