By BIRGER NORDMARK

The annual cost to the New Zealand wine industry of protecting its valuable crops from birds runs into tens of millions of dollars each year. 

Press reports early in 2006 told readers that in 2002 birds caused damage to grapes up to a value of $70 million. That amount represented only the value of lost grapes and did not include costs for preventing it from occurring.
As the industry reviews the harvest each year, the questions will be asked: was it as good as expected? If not, why not? How much of a role did birds play in any grape losses throughout the country?

The estimated value of bird-spoiled grapes sets the limit for the investment that sould be made for providing preventive measures. There is no justification for spending more money on bird trappings than what can be saved by their use.

If the result of this assessment suggests that certain steps should be taken to prevent bird damage next year, a good start is to recall what kinds of birds were trespassing on your property this year. The types of devices should be chosen to ward off the majority of local invaders, and they may vary from one region to another. Dr Valerie Saxton of Lincoln University has studied bird populations on some vineyards in Marlborough, and has reported that thrushes, starlings, blackbirds, and silvereyes were the dominating troublemakers. (Picture above: Lincoln University).

There is a general feeling that bird problems have increased over the years. Reasons for that may be found in the fact that earlier vineyards were smaller than most present ones, and other vegetation surrounded them. Newer vineyards are larger, and there is no competing food nearby around. Often planted with sweeter grapes than before, they offer a richly set-out table for large flocks of birds. Starlings in particular congregate in large flocks. It is estimated that a flock of 5,000 starlings can consume 100kg food a day.

Trade literature offers a considerable range of aids in the anti-bird war. They can be described as visual, acoustical, excluding, and biochemical repellent.

Visual
Birds have good eyesight. If they see anything strange or distressing in their flight path, they steer away. Birds have also intelligence. If they see the same event repeated over and over again without harming them, they tend to ignore it. The scarecrow would be the anti-bird strategy with the longest history. Being stationary and providing only limited limb movement, it has a rather short-lived effect. Birds soon discover that it is not harmful and then take no further notice of it.

Modern versions of visual scares come in the form of balloons with graphics of different designs - such as owls with staring eyes, a hawk with gaping mouth, etc. They may be painted in different colours, black, white, or yellow. Work in Ontario, Canada, has shown that yellow is the most effective colour. It frightens blackbirds particularly, while sparrows and finches are less deterred and robins hardly at all.

Coloured plastic tapes strung above the vine rows move with the slightest air movement. They also reflect sunlight, and from above they give the illusion of the whole vineyard in motion. Such tapes are available in yellow for deterring blackbirds and in red/silver combinations that are disturbing to a broad range of other species. Streamers of reflecting tapes have been found most effective along perimeter rows, which are usually exposed to the most severe attacks.

Mirrors and flashing lights have some use as repellents, especially when dealing with starlings. Mirrors are restricted to daylight hours, and they are said to have more effect if able to rotate. Flashing lights find use at dawn and dusk and during very cloudy days.

The 'windmill' is a variation of the ‘flashing’ theme. It is a device of usually six blades rotating with the wind. The diameter of the mill rotor may be 50-70cm. The blades are painted with UV light-reflecting paint, a method based on the finding that 50 per cent of a bird’s vision is in the ultra-violet spectrum. The spinning blades give the birds the impression of a flock of unfriendly birds flapping their wings.

Acoustical
The hearing range of birds is similar to that of humans. If people can hear a sound, so can birds, although there is some debate about the upper tone range. Conventional bird literature says that birds, like humans, cannot hear sounds in the ultrasonic range. However, manufacturers of some ultrasonic devices claim that the sound produced can be heard by birds at close quarters. The question remains open.

There is no doubt, though, that all birds can hear the blasting sound of pyrotechnic devices, and that is a very effective repellent. Gas-fired cannons are reliable bird chasers. They are available in many different configurations, from single-shot units to fully automated, electronic, randomized, rotating multi-shot units. The timing and directions of these latter ones are entirely at random. The birds cannot get used to them, because they never know when the next blast will come and what direction it will take. The sound volume is important, but it is believed that the unpredictable and unexpected sound release is of greater effect. Birds quite soon become accustomed to stationary units that shoot at regular intervals, or fire very rapidly. It is recommended to pause for at least three minutes between shots.

Most birds feed early in the morning and late in the afternoon, close to sunset. Those are the periods that need most intensive anti-bird activity. Modern gas-fired cannons can be programmed to meet that requirement and, perhaps, turn down to light or zero activity during main daytime hours.

Gas-fired cannons are capable of producing sound intensity of up to 115 dB. That gives them one drawback. They are able to irritate humans living within hearing distance almost as much as birds, but neighbours are not free to escape from the noise. Gas-fired cannons are, therefore, unsuitable for use in vineyards close to populated areas.

Pyrotechnic pistol cartridges may be an alternative to gas-fired cannons. They are fired from a hand-held pistol and generate a loud, whistling sound along their flight path. A different pistol cartridge travels silently through the air to explode high up in the air close to flocks of birds in flight. The sound of the explosion is comparable to that of a cannon shot. Both of these devices are reported effective, but they require manual operation. This would be carried out by a patrol on motorbike.

Shotguns can also be used, but their sound is produced closer to the shooter than to the birds and is less effective than the pyrotechnic devices. The chance to actually reduce the bird population by use of a shotgun is quite low.

Electronic sound equipment has been developed to a high level of sophistication. They are of different types, (1) to produce random noises that are irritating to birds, (2) reproduce distress calls that mimic individual bird species, and (3) reproduce the sound of prey birds.

The first type produces a warbling sound that interferes with the sensory system of all kinds of birds and makes them uncomfortable and insecure. The birds may be unable to communicate with each other. Used in combination with gas-fired cannons this sound keeps the birds irritated and on edge, and the cannon provides the final push to drive them away.

The second type produces distress calls of specific birds. They are effective only against the bird species, whose distress calls have been programmed on the microchip. Although they are distress calls, they sound to human ears as normal bird sounds and are not offensive to neighbours. They are usually rated at lower intensity level than the first type. Because some bird species prefer to travel together,the sound may have a deterrent effect on the travel companions as well. It has been observed that these sounds also attract birds of prey, such as hawks that mistake them for real birds’ calls. Hawks circling over the vineyard are very effective deterrents.

Electronic sonic repellant equipment is available for any size of vineyard, ranging from a single speaker to twenty, spreading bird-frightening sound over up to 20ha. Units can be loaded with different chips carrying a range of alternative sound patterns. Units are available with sound intensity output of up to 125 dB, which should prompt people working in the vineyard to wear hearing protection.  

A New Zealand inventor, John Crampton, made a notable contribution to audible bird control a couple of years ago, producing a microchip with more than 200 sounds ranging from everyday rough noises like motorbike or car engines to fine sounds of orchestral music. The inventor reckons the secret to its success is that there is no repetition of individual sounds that birds can get used to.

Excluding
Barriers of netting offer almost complete exclusion of birds from attack on vine grapes. Initially, they will cause the heaviest outlay, but in the long run they may well work out the most economic protection. Bird netting is made from UV-resistant polypropylene that is estimated to last for 10 years. Recommended mesh is 20mm for normal use or 12mm for heavy netting.

Most birds attack from above, and some are cheeky enough to perch on top of the net and peck food through it. However, some – like finches – walk on the ground and are well prepared to crawl in under the net, unless it is secured close to the surface. A considerable portion of the cost of netting is represented by the laying-out and retrieval operations, which require the use of atractor and specialised handling gear.

Biochemical
Chemical repellants have been tried in the past but have been discarded because of their potential to give off-flavours to the wine. The hope has therefore been directed to biochemical preparations. One product, claimed to be the world’s first biodegradable, food-grade bird repellant, has been developed with assistance from USDA and ruled GRAS (Generally Recognised As Safe) by the US Food and Drugs Administration. It is described as safe, effective, and environmentally friendly. It is a food-grade taste aversion agent made from the bitter, smelly part of concord grapes with the active ingredient methylanthranilate. It is sprayed on fruit and foliage to make them unpalatable to birds. Because of this quality one must assume it could not be applied during the last two weeks or more before harvest, the time when the need for protection is most acute.

Evaluation
A discussion paper, ‘An Economic Analysis of Bird Damage in Vineyards of the Marlborough Region’ published by Massey University, March 1999, contains data on assessments of the efficiency of 12 different bird control methods made by 125 participants in a survey. The perceived merits of the methods have been classified into five groups given the numerical values 5 – 1 and described as shown in the following table.

Table 1.

Although these findings are now several years old, it seems reasonable to believe they are still valid. The results are interesting; only one method, netting, has received most users’ full mark, and manned patrols on foot or motorbike making loud noises are the next best. With the development of both digital sound and pyrotechnic equipment that has taken place in the last 8-10 years one could expect them to reach a similar level of performance and acceptability.