(It is the time of year when we start receiving many complaints and queries from fruit farmers on the negative impact that birds have on orchards and vineyards. We received the following answer to one of these letters from Eric Herrman, who has done research in this field for many years. - Ed.)
There is certainly no easy and straight forward way to go about this. What the producer intends to do, such as planting a lure/sacrifice crop etc is the way to go (this is supported by the literature, mostly from Australian where they also have problems). However, the lure crop should be of similar or better quality than the crop that needs defending. There is no point in say spreading old sultanas around a crop and then expect the birds to go for these and leave the crop alone (some producers in the Orange River area tried this). The lure crop must also, ideally ripen/bloom just a little earlier than the main crop, so that birds will visit the lure crop first and establish their feeding pattern there. If they get to establish their feeding pattern at the main crop first, then the purpose of the lure crop is defeated. Best is also to plant the lure crop a short distance from the main crop. There are no set rules, since this has not been tried and tested, but i reckon at least a few hundred metres away should work. If a lure crop is too close, birds will probably not make the distinction.
As the trees are the first to bloom in the area, the birds will not be easily deterred, hence the need for a lure crop that ripens earlier and that is of similar quality. With grapes they reckon that at early ripening crops it is pointless to try and flush the birds from the vineyards, because instead of flying off far, birds just drop down into the next row and continue pecking grapes, thereby actually 'spreading' the damage. If birds have a need to get into a crop, there is no chance of stopping them - they are driven! In the Orange River area, birds survive a cold and dry winter only to find crops with sugar and juices before the first rains have fallen - what more could they want, or need. However, i should add that what birds really find attractive in ripening grapes for example, is still debated (the last time i checked the literature), so we are still not attracts birds to grapes for example.
When there are established lure crops, the use of deterrent devices such as reflective tape, sound producing machines etc, work more effectively, as the birds have a place where they can feed in peace (at the lure crop). But without a lure crop, the only option is too use a wide range of deterrent products and to alternate these regularly. The problem with gas cannons is that they are implemented in the wrong way. One actually needs to go into the orchard first with
a real firearm, and then shoot birds, so that they get conditioned to the noise associated with real danger. After this conditioning is established, one can place a gas cannon in the crop, and then of course shift it regularly, not leave it in one place for days as most producers do.
It is essential that the producer appoints a dedicated and full time person to take charge of the bird problem while it lasts. Producers normally don't like doing this cause it costs money, but is is a first wise step to reducing damage. This person can then make sure that devices are regularly moved (every couple hours) and monitor bird behaviour (where are they approaching from, what species, are the main culprits flocking species or not, is there something else that is
attracting them to the area etc). Also, the person should know the birds, and at least be able to identify the main groups and species with accuracy. Main problem species are Cape sparrow, bulbuls, white-eyes, mousebirds, olive/Karoo thrush, masked-weaver, red bishop, red-billed quelea, starlings (common, wattled, red-winged etc) and some others. Producers must also realise that birds can serve a beneficial role in crops after the main problem is over - i have seen
white-eyes feeding on insects and spiders on grape bunches after the earliest crops are harvested.
Hope this helps. You can perhaps contact Dieter Sellmeyer for info on deterrent devices. Not sure if he is still in the business, its been about 10 years. Dieter's cell: 082 446 8151 and office: 021 864 0406.