I would like to quickly sum up my experiences in the bird and bat problem area by stating that when I wished to invest in horticulture on my property at Gympie, I grew macadamia nuts. As a result of listening to the problems of rural people over many years, offering advice and evaluating results, there is only one device of which I am aware that will give horticulturists and the smaller enthusiast protection from birds, flying foxes and possums, and that is netting. The claims of success of a particular device in preventing problem species of fauna accessing a fruit crop may, I suspect, relate more to the availability of an alternative non-netted food source. With the loss of a large scale eucalypt blossom event intrastate or even interstate due to seasonal conditions such as heavy rains, or drought or fire and the birds and bats are hungry, netting is the only sure way to enjoy your fruit. The problems associated with fauna and commercial or back yard crops are well known. In 1992 Dr. Mary Bomford was appointed as National Bird Pest Co-ordinator. She collated and published a bibliography of 561 bird pest research papers from around the world and compiled a list of bird pests from across Australia plus a list of then current bird pest research activities (Bureau of Rural Resources Working Paper WP/S/92).My own personal experiences at home trying various methods to keep birds and flying foxes off various fruits has been reinforced by the experiences of growers relying on one or more of the multitude of devices that whirr, whizz, bang or pop and that is birds and animals generally become habituated to such devices quickly and will learn to ignore them within a few hours to a few days. This was also the consensus of findings from researchers both in Australia and around the world. For example, I was to learn that my early use of electric fences to deter wallabies from my $10 a tree macadamias had a fundamental error. I failed to energise those wires on the day they were erected. I can picture the local wallabies sniffing the dead wire that first night, determining it posed no threat, and ignoring it for ever after. If you wish to employ various devices as aids to repel the invaders then you will have to be active in moving them frequently or reapplying time and again. The main thrust of experience here is that once the problem species has found your fruit and brought along the friends and relations, it is too late. You must be active with your plan and deterrents in hand well before your crop ripens. If you do not have a net, then you must consider failure. I, frankly, do not have the patience, or time, to be continually applying or moving a mixture of deterrents or repellents and our time-tested remedy is to erect netting over individual trees in our mixed orchard as required. This gives us protection from the fruit piercing moth, and a degree of protection from the Queensland fruit fly. I believe it is important to have a plan of action well before your particular crop matures and that plan should be under consideration at the planting phase. Included in the plan should be a personal attitudinal review whether you want the total crop, or are prepared to share some with our fauna. I personally find it difficult to sympathise entirely with growers who claim they did not forsee problems and now see lethal methods as the only way to protect their crop, or complain loudly when they cannot obtain a permit to destroy or move the offending fauna. Society, as a whole, has generally moved on past the gun and poison pot. Whether you plant some decoy crop to ripen just before your fruit, whether you work towards covering the costs of netting and perhaps cheaper types of frames to hold that netting up, or whether (as I tend to do with, say, mangoes) consider the luxury of eating fresh tree-ripened fruit may not be practical. Our choice often involves consideration of the rapidly increasing risk of loss of individual pieces of fruit combined with insect damage, or to pick when fauna are showing interest. While not all fruit will develop that delicious home grown flavour after picking, the mango, as a current example, will continue to ripen after picking. For me it may become a matter if I can tolerate my local brush turkey - for it is just one of 150 different birds I have recorded on our property and I like to have them around - or whether it is getting more fruit than I am comfortable with. I haven’t eaten, or tried to grow – a home grown banana for some years now. I get more of a thrill in seeing the king parrots and knowing the blossom bat and local sugar glider are probably enjoying the flowers and fruit.
Electric ‘Fencing’ Sheryl asked me about the use of electric wires to deter invaders. This method relies on a series of closely spaced and tensioned wires above the crop. The method utilises a bi-polar electric fence energiser that pulses much faster that an ordinary electric fence energiser and has three terminals (instead of the normal two); positive, negative and earth. If, say, 1000 volts is carried through each wire a bird or bat coming into contact with any two wires would receive a 2000 volt non lethal shock. This method failed in commercial stone fruit orchards during a ‘bad’ flying fox year. The flying foxes were said to have ‘yelped’ when they came into contact with the wires, tumbled through and commenced feeding. Both birds and flying foxes learned to access the orchard via the undefended walls. Note that the support structure for this method is more than that required for overhead netting. This grower obtained a measure of control by applying temporary bird ban netting. Another NSW grower reported using a similar overhead wire barrier method without electricity saying that the flying foxes found no difficulty accessing the fruit through the wires but seemed to have a slight problem in leaving the orchard.
For those with a leaning towards using non lethal electricity some deep thinking is required. What is the offending target species? In back yards or small orchards this may involve a wide range of birds, especially lorikeets and honey eaters, even satin or regent bower birds, etc. What gap between wires is to be employed? What is to be done around the sides? What is your legal position if someone is adversely affected by inadvertent contact with the wires, particularly those people with heart pacemakers? Tree limbs falling may require a daily check of the system; heavy grass growth may mean extra maintenance with grass cutting or weedicide spraying. My understanding is that a permit may now be required to operate such a system.
Some considerations for those who have an electric fence energiser may provide inspiration:
N.B. Dogs react quite severely to contact with a ‘hot wire’.
Echidnas are readily killed by electrified wires placed close to the ground.
Never electrify barb wire.
Noise Research has shown that intermittent noise can actually lead to even more damage within an orchard as the birds or bats can leave a piece of fruit and return to untouched fruit within the same or a different tree. Audible devices should not be used when likely to offend neighbours. Enforcement agencies tend to be ‘reactive’ in approach and cannot now afford to ignore complaints. Noise can be a serious problem in any noise emitting device unless one has extremely sympathetic neighbours. I recall bringing a noise emitting bird scarer from Victoria many years ago and trialling it on a commercial strawberry farm as the owner looked like losing her year’s income. I understand the local council sought the advice of the Mildura Shire Council about possible complaints of noise in their area. The device seemed to work locally but neighbours took offence and stole the control unit. Model planes and helicopters could also be employed either by the owner or a model enthusiast but these are very noisy and need to be well away from neighbours. Many years ago a Victorian featured a model aeroplane look-alike hawk for $2000. I know of large scale orchards using real planes to repel birds. Other loud ‘scaring’ noises such as gas guns, hail cannons, sirens, barking dogs or shooting were the cause of increasing complaint to departmental and council officers. Birds and flying foxes become habituated to these noises. I quote the example I was given of the willy-wagtail nesting in an operating gas gun. Other less offensive noises can be generated by stringing a length of tape tightly between two anchor points. Wind will cause a vibration sound. Mine seemed to protect my vegetable garden for a short while, until the wind dropped! I had similar luck when the wind dropped and my ‘look-alike’ flying hawk dropped off into daytime slumber. Crows entered the corn patch at a point furtherest away from my somnolent raptor, a distance of about 15 metres. I have used a crow sized piece of black plastic tied to the end of a long pole to flap in the breeze. Odd growers claimed some success with this variation of a hanging dead crow method. I still utilize and frequently move the plastic should my local crows become a short-term nuisance.
Electronic sounds Two Australian scientists (Bomford and O’Brien 1990) examined the literature dealing with tests of devices that use sound to control bird damage. With the exception of distress and alarm call broadcasts (which showed potential) there was little scientific evidence to support claims of effectiveness for sonic devices in bird damage control. None of the devices reliably tested were likely to result in damage mitigation. They concluded that the value of bangers, clangers, poppers, bombers, sirens and most electronic noises on the birds and mammals tested is almost entirely limited to short-term control. The best effects were obtained when (1) sound is presented at random intervals, (2) a range of different sounds is used, (3) the sound source is moved frequently, (4) sounds are supported by additional methods such as distress calls of visual devices, and (5) sounds are reinforced by real danger, such as shooting. Much of the work in this field was carried out overseas now with varying claims of success. I am aware of different companies who currently offer devices emitting a variation of distress, alarm, and alert calls. The costs of these devices would put them beyond the reach of a small grower; close up the noise would be prohibitive. A Victorian company, Biosis Research P/L (Jaremovic 1990), was involved in the field of bio-acoustics until research funding ran out. Distress calls of some fauna may not repel, but bring others to investigate.
Bags Various bags may be worth considering but generally have a disadvantage to the grower of not readily being able to see the colour of the fruit. I quote the example of a Gympie persimmon grower facing ruin from (mainly) rainbow lorikeets some years ago. During consecutive seasons he installed 140,000 and 110,000 paper bags over his fruit and was able to harvest and make a profit. 1994 prices were 4.5 cents for each bag and 4.5 cents to install each bag. He considered the mass of white bags had a deterrent effect on birds overflying his crop. While some lorikeets did rip these bags open such damage was negligible. However, I speculate if such fruit was left just that bit longer to ripen on the tree flying foxes may have followed the ethylene gases given off during the ripening process. (Scientists advised the acute senses of these animals allow them to detect ripening fruit from a distance of 500 metres). We utilize second hand carrot/onion net bags ex supermarket stores. These do allow an idea of fruit colour, assist in keeping fruit fly and piercing moth at bay, and will break down in about 12 months if overlooked. Friendly farmers may be happy to dispose of old 40kg fertilizer bags, while a Gympie company (may) have used jute coffee bags.
Offensive Odours There are a host of substances – apart from socks used in old gum boots - which fall into the nasty odour category; they may not be popular with down-wind neighbours. As a generalization, these substances have to be re-applied after rain. I have no information as to the efficacy of using a ‘sticker’ with these repellents. As another generalization, it is/was unlawful to use a chemical on a crop for which it is not registered. For the personal use back-yarder I will merely say, ‘be careful’ of some of these substances, particularly if giving away or selling fruit. The real issue here is ‘how long does a substance repel in all weathers until efficacy is impaired and re-application required?’
While lion or tiger urine and elephant dung may be a little difficult to obtain,
Netting When I suggested netting as a solution to a particular bird or bat problem some years ago almost without exception growers responded by saying it is far too expensive. Many commercial growers went on to express amazement at the huge increase in fruit harvested after netting their crop; they didn’t know just how great their losses were. Some growers were able to recoup the netting cost within two seasons. For the hobbyist, the potential loss of prized fruit versus relaxing during the day and getting to sleep of a night means the only realistic way of protecting your fruit is to net. Small mesh netting aimed at excluding fruit fly will increase the humidity within the tree canopy which may lead to an increase in mites and mildews and loss of crop. It can also decrease the amount of light reaching the tree.
The issue, for me, in living with my furred and feathered friends, is what sort of net, where does one get it, and how is it used? I made up some samples of netting for the group. The DPI at Nambour were trying an exclusion net against fruit fly but you would build up the humidity inside the tree canopy and my experience is that you can increase the mite damage and lose a lot of your leaf with netting that dense. There are extruded nets and woven nets. Woven nets won’t snare your wildlife. Contact the DPI to find out the growers who have lost their nets and see if you can buy it.