The degree to which tropical economies depend on bats is only now being realized
The degree to which tropical economies depend on bats is only now being realized
by Marty Fujita
In tropical forests, bats often comprise close to half of all mammal species, and many plants in these forests rely on nectar and fruit-eating bats for pollination or for the dispersal of their seeds. As a result of the extraordinary variety of plants that rely on these bats to varying degrees, nectar and fruit-eating species play a key role in determining how tropical forests are structured.
Throughout the Old World tropics, from Africa to Southeast Asia and the Pacific Islands, flying foxes (bats of the family Pteropodidae) are also of great importance to plants that contribute hundreds of millions of dollars annually to national economies. Despite the value of flying foxes, their populations have been decimated by large-scale eradication efforts, habitat destruction and over-harvesting for human consumption. It is believed that more than a dozen species of flying foxes already are either extinct or endangered. Vast numbers of these bats are required to ensure adequate reproduction and propagation of some rain forest plants, yet in many places too few remain to fulfill their vital role. So little attention has been paid to the plight of flying foxes that some have become extinct before they were even declared endangered, and the status of many more remains in doubt. Their loss could have significant consequences for many bat-dependent plants and the ecosystems and economies they support.
The need for documentation
Protection for flying foxes is urgently needed, but misconceptions about them have made it difficult to convince governments and even conservation planners to provide necessary management and conservation initiatives. In some countries, all bats are officially listed as vermin, the status otherwise reserved for rats, mice and poisonous snakes. Documentation of the values of flying foxes to rain forests and associated economies is essential in order to gain protective legislation for declining species.
In 1985, Bat Conservation International received a grant [BATS, February 1985] to investigate and document the economic value of flying foxes in the Old World tropics. Because of my previous experience and special interest in these animals, I was chosen to carry out the study as part of my BCI-sponsored post-doctoral fellowship at Harvard University. The work was conducted in three stages, the first of which involved an extensive review of both botanical and zoological literature to compile a comprehensive list of plants visited by bats for fruit, pollen or nectar. The marketable products derived from these various plant species were then documented, and the countries which produce them, the origin of each plant species, and current distribution of the plant were noted. This phase revealed that the majority of reports of economically important products derived from bat-dependent plants were from Southeast Asia, and that area was chosen for the third stage of the study: on-site documentation of the economic values of these products. Economic botanists were consulted, and extensive interviews were conducted in markets throughout Southeast Asia during the summer of 1987. (Scarcity of such reports from other areas where flying foxes occur likely reflects only a lack of field investigation.)
"Bat plant" products
I documented over 300 plant species in Southeast Asia, tropical Africa, and the Pacific islands that rely, to varying degrees, on flying foxes for pollination or seed dispersal. At least 134 of these plants yield products that are used by humans. Most of these plants are not grown on large commercial plantations, and thus still rely on bats. More than 450 products, including medicinals, food, drinks, fruits, dyes, tannins, timber, fiber and fuelwood, are derived from these plants. Although most products are important only in local markets, a number of them are also valuable export items. The potential of others, such as medicinals, has not yet been fully explored. The importance of bats to the future harvest of these products is substantial, and has largely gone unrealized or has been vastly underestimated.
Bananas, originally from Southeast Asia, are one of the best known tropical fruits and, perhaps, the most commercially important. Wild bananas are pollinated almost exclusively by bats, with at least 20 species of the plant known. Only a few kinds are cultivated, and these do not need to be pollinated to produce fruit. Nevertheless, wild plant species provide important genetic reservoirs for cultivar improvement and for combating disease, such as fungal root rot. Their loss could seriously threaten the future of commercial banana production.
In Southeast Asia, the durian (Durio zibethinus) is known as the "King of Fruits." By some estimates, the durian harvest is worth $120 million annually to producing countries. Durian flowers are pollinated by flying foxes, especially the Dawn bat (Eonycteris spelea). The large white flowers are perfectly adapted for bats. Clustered on the underside of sturdy branches that provide easy access, they exude copious amounts of nectar, opening only at night when bat visitors are most active, enticing them with a fragrant odor. The fruit is one of the most delectable delights of Southeast Asia.
Another "bat plant" that produces valuable export products is kapok (Ceiba pentandra). Although this species probably originated in Central and South America, it is now common in Thailand, Malaysia, Indonesia, the Philippines and certain parts of Africa. Throughout its range, it is pollinated by bats, and its seed pods contain high-quality fibers used for insulation and as stuffing for life-jackets, cushions and mattresses. In Indonesia alone, 1986 statistics indicate that kapok fiber was worth over $5 million in exports. The importance of kapok has diminished with increased use of synthetic fibers, but it is still valued locally, and kapok trees are commonly planted in villages. Other products derived from this plant species, such as oil and timber, are becoming more important.
Throughout the Old World tropics, timber from bat-dependent trees is used in many ways--for furniture, small carvings, canoes, building materials, poles and fuel, to name just a few. Although economic statistics are not available for many of these products, tests on the various qualities of wood from bat-dependent trees indicate that many of them have the potential to be marketed profitably. For example, Pajanella longifolia, a Southeast Asian tree pollinated by flying foxes, is known for its dense, teak-like wood which is used for canoes, boats and house planking. Many of Australia's Eucalyptus trees, as well as brush box (Lapostemum confestus), black bean (Castinospermum australie) and others, also are pollinated by bats and yield excellent, commercially important timber. In Africa, the wood of the iroko tree (Chlorophora excelsa) is highly valued because of its resemblance to teak. Azadirachta indica, introduced to West Africa from India, is an important tree for fuelwood; its seeds are dispersed primarily by bats, which may have caused its rapid spread over large areas.
Statistics on products not exported were unavailable, so I conducted market surveys in Malaysia and Indonesia to assess the economic importance of some of these. One product, petai seeds, was found in every market I visited and appears to be a very popular food item. Petai (Parkia speciosa and P. javanica) are large leguminous trees (of the bean family), native to Southeast Asia. They are not grown commercially, but are found in small plantings around villages and are relatively common in native forests. The light-bulb shaped inflorescences of these trees are suspended from pendulous stalks, permitting easy access to bat pollinators. The long, green seed pods are collected mostly from forest trees and taken to local markets. The petai seeds are prized for their garlicky taste and are used to flavor curries and other traditional dishes. The Forest Institute of Malaysia estimates the local value of petai at over a million dollars annually in Peninsular Malaysia, not including its potential value as a timber tree, a use which is now being tried experimentally.
Sonneratia trees are also important on a local scale in Malaysia and Indonesia, comprising a major component of the mangrove flora of Southeast Asia and Australia. Their showy, nocturnal flowers are primarily pollinated by three small flying foxes, the Dawn bat (which also pollinates durian), the Common long-tailed bat (Macroglossus minimus), and the Lesser short-nosed fruit bat (Cynopterus brachyotis). Wood from these trees is used for poles, furniture, sandals, and in the production of charcoal. Mangroves also serve as the major roosting sites of two of the world's largest flying foxes, the Common flying fox (Pteropus vampyrus) and the Island flying fox, (P. hypomelanus). In addition, mangroves have incalculable value as fish and shrimp breeding grounds.
Currently, vast mangrove areas in Sarawak and Sabah (the Bornean provinces of Malaysia) are being cut for paper pulp. The combined importance of mangroves to the ecology of flying foxes and their potential commercial value make a sound management plan essential.
The decline of flying foxes
Despite the importance of flying foxes to the ecology of Old World tropical forests and their considerable contribution to local and national economies through the plants that depend on them, the few accurate censuses recently conducted indicate that many of these bat species are declining rapidly. In general, very little is known about the distribution, numbers and behavior of Old World flying foxes. Most detailed studies on the ecology and behavior of bats have concentrated on species found in Europe or the United States. A few historical, anecdotal accounts from Southeast Asia, Australia, the South Pacific Islands and parts of Africa, speak of vast colonies of flying foxes, far larger than most that remain today.
Although habitat destruction has played a large role in their decline, colony eradication by fruit growers, and unregulated hunting (for sustenance and sport) appear to be major causes of population declines in Southeast Asia, the Pacific and Indian Ocean islands, and increasingly in Africa and Australia. A number of Southeast Asian flying foxes, especially the smaller cave-dwelling species, are taken from their cave roosts. Some of these are already extinct, and others soon may be if not protected.
To determine the degree to which hunting was affecting bat populations in Malaysia and Indonesia, I conducted interviews with sport and bounty hunters, market vendors and restaurant owners from many different regions of these countries. Although the majority of Malaysians and Indonesians are Moslem and are not permitted to eat bats for religious reasons, the large Chinese and Manadonese populations of these countries consider bat meat a delicacy. According to many Chinese, bat meat is also the best cure for asthma, kidney ailments and general malaise. My interviews and my observations indicate that the only species traded to a significant extent in Malaysia and Indonesia is the Common flying fox; the Island flying fox may also be hunted to a limited degree. Many smaller species, such as Cynopterus, are not actively hunted for food, but they are shot when they visit fruit orchards.
Many orchard owners in both Malaysia and Indonesia consider flying foxes to be pests, especially of rambutan (Nephelium lappaceum), langsat (Lansium domesticum), and water apples (Eugenia aquea)--all important market fruits. I questioned a number of growers about bat damage to their fruit crops. Given the number of bats shot as pests, I was surprised when most told me that squirrels and macaques were a more significant problem than bats. The former take both ripe and unripe fruit and were, therefore, a threat during the entire growing period. Bats, on the other hand, take only ripe fruit and present a problem to growers only for a few days prior to harvest.
The owner of one of the largest langsat orchards in Peninsular Malaysia told me that if he did not protect his trees from bats during this period, 20% of his crop would be lost. However, if he took simple protective measures, such as shining bright lamps, lighting small fires below the trees or shooting to scare the bats away, the damage would be negligible. He also told me that almost all of the langsat trees in his village, which are harvested for sale in the local market, were the result of seeds dropped by bats. During the fruiting and flowering seasons, many plantation owners employ bounty hunters to eradicate animals they consider to be pests. Bats, primarily the Common flying fox, command a bounty as high as two U.S. dollars. Typically, a group of three to five hunters patrol an orchard at night, locating bats with bright lights. As many as seven can be hit with a single shot, according to one hunter, and 100 or more taken in a single night. Others, hunting only for sport, shoot bats at their daytime roosts, and it is not uncommon for a group of hunters to bag several hundred in a single outing. When bats are to be sold in markets, different hunting techniques are employed to capture the bats live since customers prefer them fresh. The bats are then killed on-the-spot by the vendor.
The volume of bat meat traded is difficult to estimate. However, the figures reported by individual vendors indicate that the annual sales of a single merchant could eliminate several average-sized colonies (about 1,500 animals each) of Common flying foxes each year. In the Sunday market in Kuching, Sarawak, I found a vendor who sold this species exclusively, selling 150 to 200 every week for about three U.S. dollars each. Although only a few were found who specialized in bat meat, wild game vendors were found in many markets. On several occasions, these merchants (who displayed monitor lizards, freshwater turtles, squirrels and snakes) obligingly told me that bat meat could be easily obtained if I wanted to order it. Bats were also readily available in Manadonese restaurants in Indonesia, and one owner told me that she sells as many as 2,000 flying foxes each year.
Because no historical data on bat populations exists for these areas, it is difficult to assess the actual impact that commercial hunting of bats has had on the various flying fox species in Southeast Asia. All the hunters I interviewed, said that in the last 10 years or so, colonies of Common flying foxes have become increasingly difficult to locate, and the number of bats shot in orchards has decreased substantially.
One factor that may contribute significantly to flying fox decline is that the greatest amount of hunting occurs during the bats' reproductive season. Many of the hunters and vendors interviewed stated that there was a definite "bat season" that coincided with the main fruiting peaks in the area, and that a number of the bats taken were pregnant or carried young. Many bat species in tropical regions are known to time lactation with fruiting peaks. Increased hunting during such a crucial period could severely limit a population's ability to recover.
Much more information is needed about the number of colonies and the population densities of flying foxes in Southeast Asia before their status and conservation needs can be fully determined. Available information strongly suggests that at least two species, the Common flying fox and the Island flying fox, are threatened. Although they both are protected in Peninsular Malaysia, the schedule on which they are listed only guards against importation, exportation or hunting them for trophies. It does not require that a license be obtained for hunting or selling, nor does it limit the numbers that can be taken. This legislation applies only to Peninsular Malaysia, and not to Sarawak or Sabah. Furthermore, general legislation in Peninsular Malaysia concerning wild animals states that any animal which poses a threat to a resident, or to his or her crops, can be killed. Since bats are considered fruit pests, they are hunted freely under this provision. No laws protect any bat species in Indonesia.
Increased awareness of the vital role that these bats play in the life cycle of commercially important plants can have very positive effects on conservation efforts. More research on the ecological impact of fruit and nectar-feeding bats is essential. With better documentation of the ecological and economic values of bats, we increasingly are able to alert governments and conservation organizations to the urgent plight of flying foxes. Protective actions must be taken before more populations fall too low to perform their essential role in the maintenance of tropical forests and the economies they support.
Marty Fujita obtained her Ph.D. degree studying the evolution, behavior and ecology of bats at Boston University in 1986. Funded through a BCI post-doctoral fellowship, she worked on BCI's flying fox project while a research associate of the Museum of Comparative Zoology at Harvard University. She is currently a Diplomacy Fellow for the American Association for the Advancement of Science, working as Assistant Environmental Advisor for the Latin America and Caribbean Bureau of the U. S. Agency for International Development.
Dawn bats are major pollinators of flowers of durian fruit, yet this important crop is increasingly threatened by dwindling bat populations. These bats are now uncommon in a number of places where they were once abundant. PHOTO BY MERLIN D. TUTTLE
A durian tree in fruit on a steep hillside on Penang Island, Malaysia. The great natural historian, Alfred Russell Wallace, once wrote that it was worth a trip to Southeast Asia just to experience this fruit. PHOTO BY MARTY FUJITA
Kapok is pollinated by bats throughout its range from Latin America to Asia, Africa, and the Pacific islands. This one is being visited by and endangered Marianas fruit bat (Pteropus Mariannus) on the island of Guam. PHOTO BY MERLIN D. TUTTLE
Below: Dr. Fujita interviewing a petai vendor in the large Chinese Chow Kit daily market in Kuala Lumpur, Peninsular Malaysia. The long green petai pods sell for 50 cents to a dollar for a bunch of five.
Right: A vendor at the Sunday market in Tuaran, Sabah, Malaysia. The fruits she sells are all from bat-dependent plants. From left right: durian, yellow and red cooking bananas, and mangos. PHOTO BY MARTY FUJITA
A mixed colony of Lyle's flying foxes (Pteropus lylei) and Common flying foxes (P. Vampyrus) leaves their tree roost at twilight to feed. The Lyle's flying fox seen against the sky is huge with a wingspan of three feet, but the Common flying fox can be twice as large. PHOTO BY MERLIN D. TUTTLE
A Greater short-nosed fruit bat (Cynopterus sphinx) eagerly licks the nectar reward from the blossom of a wild banana plant. Its face will soon become covered with pollen which the bat will carry to the next plant, thereby ensuring that the plant will bear fruit and continue the cycle. PHOTO BY MERLIN D. TUTTLE