by Merlin D. Tuttle
Many Old World fruit bats have been killed in mass eradication efforts aimed at protecting commercial fruit crops. Studies dating as far back as 1931 cast serious doubt on these largely unsubstantiated claims, but eradication efforts continue. Several species of large fruit bats already are extinct, and others have been drastically reduced in numbers. One recent Mid-Eastern campaign led to the poisoning of numerous caves, even in nature preserves, indiscriminately destroying entire cave faunas. Ill-advised extermination continues in many places. In Australia legal protection has just been withdrawn, and attempts to kill fruit bats are anticipated.
Recently, a farmer from near Mombasa, Kenya, informed me that he hated fruit bats. He claimed they destroyed his mango crops. On 10 March 1984 1 visited his farm and found only monkey-caused damage. This led to my investigation of 15 farms over an area of more than 2,500 square kilometers, south of Mombasa.
In the period 1 0 through 29 March I learned to identify tooth marks of monkeys, bush babies and bats that fed on mangos there, and examined 7,470 mangos for damage. Five hundred and eighty-nine had been partly eaten. Of those, monkeys damaged 498 (84.5%), bush babies 61 (10.4%) and bats 30 (5.1 %). Most importantly, all mangos eaten by bats were ripe to very ripe. Bush babies restricted 96.7% of their feeding to similarly ripe fruits. In contrast, 60.9% of fruits damaged by monkeys were still too green for harvest.
Twelve of the farms investigated consisted of small family plots that were virtually unmanaged except for sporadic efforts to chase monkeys away. Ripe mangos were simply eaten by owners as they fell. On these farms, only 799 mangos (10.7% of total sample) were examined, yet they included 546 (92.7%) of those damaged. On the four remaining farms people were hired to keep monkeys away, and mangos were harvested at regular intervals throughout the two annual seasons. Those for export were picked 5-7 days prior to ripening, and any within 2-4 days of ripening were sold locally. On these farms I examined 6,671 mangos as they were picked. Monkey damage was limited to 39 mangos (0.6%) and only four mangos had been eaten by bush babies or bats. These were very ripe and, according to the owner, had been lost when pickers missed them in the previous harvest.
I also studied the ripeness preferences of 18 epauletted bats (Epomophorus gambianus, E. labiatus and E. wahlbergi), 7 Straw-colored Fruit Bats (Eidolon helvum), 3 Egyptian Fruit Bats (Rousettus aegyptiacus) and 3 Angolan Fruit Bats (Rousettus angolensis). The bats were caged in a 10xlO foot square enclosure and tested in two separate experiments covering a total of eight nights at two localities. On three nights the bats were offered only store-bought mangos that were not quite ripe, and on five nights they also were given similarly unripe bananas, avocados, papayas and guavas, all purchased at local grocery stores. On nights of testing only these fruits were provided in the 18-hour period from 6 a.m. until midnight.
Fruit bats normally eat at least their own body weight nightly, so these were almost frantic in their search for food by the end of an experiment. Even so, the slightly green fruits were consistently ignored. Each night at midnight, when I provided ripe fruits of the same kinds, the bats typically met me at the cage door and grabbed them directly from my hand.
Both my field and captive observations exonerated the bats in question, since no fruit of harvestable ripeness was taken. In this case many bats visited even the best managed mango farms, and they undoubtedly ate many mangos. The important point is that mangos ripe enough to attract bats were too ripe for harvest and were lost to the owner whether or not bats found them. Captive observations indicate that this would be typical for other fruits as well.
I especially thank the owners of the M'Sangani Estate, Mr. and Mrs. Akberkhan S. Khan, for their kind assistance with this study. They reportedly are the largest exporters of mangos in Kenya, with annual crop values averaging roughly 2,000,000 Kenyan Shillings ($150,000, U.S.). They have been harvesting mangos from their 1,200 trees for more than 10 years. Much more knowledgeable than most farmers, they considered my study to be an unnecessary exercise in demonstrating the obvious.
(Editor's Note: BCI would welcome any information pro or con on the subject of fruit bat damage to crops. Investigation and resolution of even perceived problems involving fruit bats is essential to their conservation.)
One of the Egyptian Rousette Bats (Rousettus aegyptiacus)
used in the study of supposed crop damage enjoys a meal of very ripe mango. Photo courtesy Merlin D. Tuttle.
Mrs. Akberkhan Khan grades mangos while her assistants pack them for export to Europe and Saudi Arabia. Mrs. Khan and her husband own the M'Sangani Estate where Dr. Tuttle studied the impact of fruit bats on mango harvests. Photo courtesy Merlin D. Tuttle.