The four Australian Flying Fox species, Pteropus scapulatus, P. poliocephalus, P. alecto and P. conspicillatus, are found in eastern and northern coastal regions. They are gregarious and live in colonies containing as many as 250,000 animals at densities of up to 20,000 to the acre.
The bats feed on ripe, native and cultivated fruit and blossoms. For much of the year, Eucalyptus blossom is the most important food and its abundance regulates the number of animals in a district. It has been claimed that bat numbers increase proportionately with the number of fruit trees planted.
In past years, bat camps were infested with numbers of carpet snakes which helped to limit the bat population. Most of these snakes have since disappeared.
Over the years, farmers and scientists have come up with an amazing number of schemes to try to deter this voracious pest. It seems the fox's appetite is equal to, if not better than, man's ability to protect the much-prized fruit.
The following are just some of the methods used, past and present, with varying amounts of success. Lights placed in and around fruit trees. These include, continuous illumination, flashing lights, strobe lights, coloured lights and extremely bright high voltage arc lights (imitation lightning). All have proved ineffective after a time when the foxes became used to them.
Sirens, horns, bells, jangling metal, tin foil and high-frequency ultra-sound devices. Also recorded distress calls and wing-flapping noises. All of which are only partially effective.
Explosive noises are reasonably effective but are slightly detrimental to the farmer's sleep pattern. Scarecrows only help to guide the foxes in to the best trees. Fires, smoke and various gases have been tried, but are generally costly and time-consuming to maintain, and the foxes soon learn to keep to the windward side. A mixture of sawdust, kerosene and sulphur produces a pungent smell, but its effectiveness varies with wind changes. Phenol and carbolic acid odour are equally difficult to direct. Acetylene gas from carbide rocks in waterproof containers (use beer cans with the top flanged inwards and hung upside-down) are effective if enough are placed in each tree - usually about 8. This is rather time-consuming and the rocks only last 5 to 6 days in dry weather and 2 days in wet weather. The gas is heavier than air and the tins have to be placed high in the tree.
Flame throwers have been used but with rather destructive side-effects.
Explosives have also been used in the past with devastating effects on the trees. Some foxes were killed but the majority were merely assisted into involuntary flight. Public support for this type of operation was less than enthusiastic.
In China, small huts are erected above the lychee trees and occupied by a guard who keeps a look-out for both winged and wingless foxes. Swaying bamboo poles are also used.
Introduced diseases such as Salmonella have also failed to infect flying fox colonies. Bounties and attempts to encourage commercial use of bat skins have also failed.
In the Solomon Islands, bats have attacked pineapples. When disturbed they scramble to the nearest tree for take-off. Local farmers have become quite fast with a wooden knocker.
In South America, nets have been used to cover the fruit trees but the bats have learned to crawl up the trunk, bypassing the protective net.
In some areas of New Guinea the mangoes are picked and eaten green to beat the foxes. Poisoned fruit have been locally effective but are dangerous to non-target species and consumers.
Fruit bats will not eat fruit which are too close to green-ant nests.
Barbed wire strung above fruit trees is an effective deterrent but may be too costly for a commercial operation. Tall pawpaw or banana trees planted in or around orchards keep the foxes off the main crop and also offer an easier target for shooting. This system also eliminates shotgun damage to the main orchard crop.
In the South Pacific region, many natives consider roasted flying fox a delicacy. However the practice is not widespread enough to reduce numbers.
In Cairns, North Queensland, a helicopter was used to frighten off a camp of flying foxes which was polluting the area with their smell and noise. However they moved their camp only a few hundred metres.
Dog collars have been placed around pawpaw trees to protect the fruit with the owners claiming good success.
Chemical sprays on mature fruit have been tried. Sulphur is effective for a few days but the bats soon return. 'Bayer Mesurol 75' has been sprayed on fruit and claims of up to 2 weeks protection have been made. Application is 200 g per 100 l of water.
The use of 1-inch mesh nylon nets specially made for fruit trees has proved quite successful. Not only are the bats kept out but also fruit-sucking moths, elephant beetles and birds. As an extra bonus the nets also snare any visiting tree snakes. After that the smell keeps everything away.
The first flying foxes to visit an orchard are referred to as pioneer bats and are said to communicate the message back to the rest of the gang. I have never yet seen a flying fox leave a juicy ripe fruit to go back to tell the others; and by the abusive screeching they let out when another bat comes near their feeding area, it's hard to believe they communicate any message at any time about the location of ripe fruit. I think ripe fruit communicate their own whereabouts by their colour and odour, and the foxes have very good night vision.
Most previous research has recommended shooting the early pioneer foxes as this may discourage later arrivals. However, bats tend to feed on their own and then move on, and may arrive at your orchard at any time through the night.
Fruit bats have now reached plague proportions and consideration should be given to culling them back at least to their original numbers.
Editor's note: flying foxes are now protected animals and as such cannot be culled.
DATE: November 1983
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