Fruit bats, also known as flying foxes, are a diverse group of mammals with specialized dietary adaptations. Understanding their nutritional needs is crucial for both conservation efforts and maintaining their health in captivity. This article explores the diet and nutritional aspects of fruit bats, covering their natural food sources, adaptations for consuming sugary fruits, dietary considerations in captivity, and the ecological roles they play.
Natural Diet of Fruit Bats
Fruit bats exhibit a wide range of feeding strategies, primarily consuming fruits, nectar, pollen, leaves, and bark. Some species also supplement their diet with insects and other invertebrates found on fruits and leaves. As their name suggests, fruit bats are frugivorous, feeding on fruit, berries, leaves, and bark, sometimes taking nectar and pollen, and invariably a few insect larvae that dwell on leaves and fruit. These bats often pick the fruit from the tree and return to a feeding roost where they will eat it. The fruit is crushed and the juices and soft parts swallowed; some seeds will be spat out, others are eaten and pass out later in the bat’s droppings.
Specific Food Sources
In the wild, Rodrigues fruit bats consume a variety of aromatic ripe fruits, including wild figs, guavas, bananas, breadfruits, mangoes, and papayas. They also consume the flowers and leaves of local and introduced plant species.
Nutritional Adaptations
Fruit bats have developed several adaptations to thrive on a sugar-rich diet. Unlike humans, who can develop diabetes from excessive sugar intake, fruit bats have evolved to efficiently process large amounts of sugar. Research has shown that Jamaican fruit bats have more insulin-producing and glucagon-producing cells in their pancreas compared to insectivorous bats. Their kidneys are also equipped to handle the large amounts of water from fruit while retaining the low amounts of salt.
To understand how fruit bats evolved to consume so much sugar, biologists and bioengineers have been studying the genetic and cellular differences between fruit-eating and insect-eating bats. Approximately 2% of DNA is composed of genes, which are segments of DNA that contain the instructions cells use to create certain traits, such as a longer tongue in fruit bats. The pancreas regulates blood sugar and appetite by secreting hormones like insulin, which lowers blood sugar, and glucagon, which raises blood sugar. The kidney filters metabolic waste from the blood, maintains water and salt balance, and regulates blood pressure.
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Some fruit bat species, such as the Mexican long-nosed bat (Leptonycteris nivalis), have a specialized brush on their tongue to help in the collection of nectar.
Dietary Considerations in Captivity
Maintaining a balanced diet for fruit bats in captivity is essential to prevent health issues such as obesity and nutrient imbalances. Cultivated fruits do not duplicate the nutritional composition of fruits consumed by wild bats, so they should be avoided when feeding captive herbivorous bats.
Recommended Diet Components
Nutrient requirements for captive herbivorous bats can typically be met by feeding a diet high in vegetables, supplemented by a suitable complete feed for bats or similar mammals. At the Zoo, Rodrigues fruit bats eat fruit nectar fortified with vitamins and minerals, fresh fruits, and vegetables.
Iron Storage Disease Prevention
Frugivorous bats should be fed a diet that contains a low amount of iron (400 mg/kg of dry matter) to prevent iron storage disease (hemochromatosis).
Feeding Habits and Ecological Roles
Fruit bats play crucial roles in their ecosystems through seed dispersal and pollination.
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Seed Dispersal
When fruit bats consume fruits with small seeds, some seeds that get swallowed do not get digested but are carried and deposited away from the tree source. These seeds grow and become the lush green rainforest.
Pollination
Some species of fruit bats have a specialized brush on their tongue to help in the collection of nectar. As they feed on nectar, they also facilitate pollination, contributing to the reproduction of various plant species. A black flying fox (Pteropus alecto) feeds on silky oak flowers, playing a vital role in pollination.
Diversity in Bat Diets
On a global scale, bats consume a wide variety of foods, including fruit, leaves, bark, nectar, pollen, winged insects, beetles, bugs, termites, spiders, small mammals (especially rodents), birds, lizards, amphibians (especially frogs), scorpions, other bats, and fish. While fruit bats are primarily herbivorous, other bat species exhibit different feeding habits.
Insectivorous Bats
All British bat species, indeed 70% of the world’s bats, are insectivorous and/or arachnivorous (eat spiders), although microbats elsewhere in the world will eat other prey. UK bats have teeth typical of insectivores: sharp incisors and canines for gripping and biting, with cusped cheek teeth to cut and break up the food. During the summer months, our native bats emerge shortly after sunset and hunt actively for a few hours, returning to their roosts shortly before dawn. Favored feeding grounds may be several kilometers from their roosts, and some species spread out and hunt in a defined territory.
Captive insectivorous bats frequently are fed diets consisting primarily of mealworms. Crickets, fruit flies, morio worms (superworms), blowfly larvae, and other insects also are commonly offered. Because insects typically are low in calcium, they should be maintained on a calcium-enriched diet so the bats will consume the insects' high-calcium gut contents. A suitable mealworm diet can be formulated using 35% wheat middlings, 35% ground dry dog or cat food, and 30% ground calcium carbonate, which should be fed to mealworms for at least 3 days. Gels containing water and a calcium solution can also be fed to gut-load mealworms.
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Carnivorous Bats
Some bats will tackle prey larger than most fly insects. In the forests of Panama, for example, the spectral bat (Vampyrum spectrum) will take small mammals (mainly rodents), and the greater bulldog bat (Noctilio leporinus) catches and eats fish. Some bat species are even known to feed on their diurnal counterparts, birds, although such phenomena are rare. In a 2001 paper for the Proceeding of the National Academy of Sciences, Carlos Ibanez and colleagues reported on bat predation of nocturnally migrating birds. The biologists analyzed 14,000 fecal pellets of the greater noctule (Nyctalus lasiopterus) and reported that this species catches and eats large numbers of migrating Passerines. Passerines are a group containing almost half the world’s bird species, often referred to as “perching birds” and include sparrows, thrushes, flycatchers, robins, and starlings.
Vampire Bats
Perhaps the most notorious feeding method seen in the Chiroptera is that of sanguivory, or blood-drinking. Vampire bats are native to the Americas, from Mexico to Brazil, Chile, and Argentina. A mature common vampire bat has a wingspan of only 35 to 40 cm (14 - 16 in), is seven to nine centimeters (about 3.5 in) long, and weighs in at between 15 and 50g (0.5 to about 2 ounces). Vampire bats have three infrared pit organs in their nasal sac, which have a heat-sensing function and help them gauge the best place to cut. Vampire bat saliva is known to contain an anticoagulant, nicknamed “Draculin” but more formally known as desmoteplase, which prevents the blood from clotting while the bat feeds.
Conservation and Public Education
Many fruit bat species face threats such as habitat loss and hunting. Conservation efforts and public education are essential to protect these important animals.
Rodrigues Fruit Bats: A Case Study
Rodrigues fruit bats were once abundant on Rodrigues Island until the mid-1900s. A marked decline occurred in the 1970s, and following Cyclone Celine II in 1979, the population was reduced to around 70 bats. In 1998, the Philadelphia Zoo established the first environmental educator on Rodrigues to help inform the locals about conservation to make sure this bat never comes so close to extinction again. The Zoo is one of the few zoos in the nation that has a breeding group of these endangered bats.
American Samoa's Fruit Bats
Large flying foxes, also known as fruit bats, are one of the more unusual animals in American Samoa, especially for visitors from areas where bats are small and rarely seen. Three species inhabit the islands - two large fruit bats (Pteropus samoensis, P. tonganus) and a small insect-eating bat (Emballonura semicaudata). The two flying foxes are especially distinctive: they are renowned for being large (with a wing span up to 3 feet wide) and active both day and night. Pteropus samoensis (pe'a vao) is commonly called the Samoan flying fox. The other flying fox, Pteropus tonganus (pe'a fanua), has several common names such as the Insular, White-naped, White-necked, or Tongan fruit bat.
During the daytime, pe'a fanua form large roosting groups or colonies of hundreds to thousands of bats. These colonies are generally organized according to their reproductive status and may be composed of bachelor males, clusters of females defended by an adult male (suggesting a harem mating system), or groups of females and their young. But the pe'a vao does not do this. Instead, these bats usually roost singly on branches, or as pairs of males and females (suggesting a monogamous mating system), or as a female with its young.
Although their name indicates that they are fruit-eaters, both species also eat nectar, pollen, leaves, and sap. They tend to consume only the “juice” of fruits and leaves. To do this, a bat will carefully chew on food (usually eating around large seeds), press the pulp against the roof of its mouth with its tongue, squeeze and suck in the juice, then spit out most of the pulp in pellets called “ejecta.” These ejecta are especially abundant under breadfruit trees ('ulu) where the bats have been feeding overnight.