DEVELOPMENTS IN BIRD CONTROL

Press, Volume CIV, Issue 30823, 7 August 1965, Page 8

DEVELOPMENTS IN BIRD CONTROL

Bird control methods in use today range front modifications of the traditional scarecrow to a wildlife version of the controversial “pill.”

In some places, unwanted birds are frightened by broadcasts of their own distress calls: in others predatory animals are released to attack them or their eggs; and in others again their perching places are treated with sticky substances. They are given electric shocks, poisoned outright, drugged into immobility, caught in traps or nets, subjected to highfrequency sounds or various explosive noises, chivied away from their breeding areas, tricked into sitting on eggs that will not hatch, starved out by removing their food sources, or simply shot. These are some of the methods described by Dr. P. C. Bull, senior zoologist of the Animal Ecology Division of the Department of Scientific and Industrial Research, in a report on overseas bird research, which he surveyed in the course of i study tour last year. Not all these methods are successful or economic. Many [ of them cost more than seems justified by the bird damage they are designed to[ prevent; some cause more; disturbance to neighbours j than to birds: and many have only limited or temporary [ effect. Dr. Bull found that almost all bird control methods in current use fell into one or another of four general groups. These, and some of his observations on them, are as follows: (1) Modification of habitat. This requires research to [determine what it is about (an area that attracts undesirable birds, and then involves ! attempts to make it less at-1 (tractive. Undoubtedly the j

best approach wherever practicable. involves such practices as removal of sources of food which enable birds to overwinter in the area, control of insects that help to attract birds, removal of cover and nesting sites, growing crops in dense rather than open stands, and encouraging “buffer” plants that are attractive to birds at the times when crops are vulnerable. Illustration A good illustration of environmental manipulation is provided by recent Australian work at Sydney airport, where silver gulls. spurwinged plovers and starlings were a danger to aircraft. The gulls were largely removed by better management of rubbish dumps which had i provided them with food, and [by draining shallow ponds [ where they roosted. The ’ plovers and starlings had been attracted by worms and insects on grassy areas be[side the runways. When this attraction was removed by treating the ground with the insecticide telodrin. the birds! left—perhaps because the ; chemical irritated their feet as well as removing their food. Telodrin, however, cannot be used on land which drains into trout streams' or on to pastures.

(2) Protection by netting. Wire netting gives complete protection, but is too expensive except for small areas of particularly valuable perennial crops, and the netting may also obstruct harvesting. Cheaper, weatherproofed paper-fibre netting now available in the United States, however, can be spread over permanent frames while the

crop is vulnerable, and then rolled up and stored till the next season. (3) Frightening devices. These range from modifica-' tions of the classical scare-j crow to elaborate installations! for broadcasting amplified > distress calls. Most give some’ temporary benefit, but are! costly in labour and materials.! Carbide exploders and like de- ’ vices are effective for some] species, but birds get used to I them sooner than do non-: fruitgrowing neighbours. Much research has been de-j voted to the distress-call! method, and fixed and mobile; equipment for broadcasting! such calls has been used overseas with variable results.! Possible reasons for the fre-l quent failures of this system! are poor recordings, distor-l tion of calls by the amplifier,! excessive or wrongly-spaced ‘ use of calls and the existe -,ce of local “dialects” in defferent; populations of the same! species of bird. In. America it has been suggested that better results! might be achieved with a combination of sounds, including the alarm call of the tar-1 get species, the calls of hawks: or other predators, and then the distress call of the target! species. A better understanding ofi [the significance of sound in ! bird behaviour may be neces-l sary before the distress-call, system can be developed prop-! erly, and biological studies in i this field are now being carried on in Australia and• ! America. (4) Shooting, trapping and poisoning. Shooting is more effective in frightening birds than in reducing bird populations. Traps and nets, with a few exceptions, rarely catch enough birds to be useful as routine controls. Poisons give more impressive results, but generally involve danger to other animals and to man. 1 The most promising poison. , now under test in America, is I

a compound known as DRC 1339. This is 50 to 100 times more toxic to birds than to mammals, seems to be readily taken by starlings and black- ! birds, is relatively safe to mix, land has a low risk of second[ary poisoning. Another interesting substance used experimentally in. Britain is alpha-choralose. At low concentrations, this merely immobilises birds, so that pest species can be destroyed and others allowed to recover. At greater concentrations, alpha-choralose is lethal, and its effectiveness as a poison against sparrows has been confirmed by recent trials in Hawke's Bay. Apart from these main groups of control methods, various other approaches are being explored—the most interesting being the use of chemical sterilants, which, when fed to birds by means of baits, inhibit their reproduction. Work on this method is still mainly in the laboratory stage, but an American field trial with triethylenemelamine resulted in the hatching success of red-winged blackbirds being reduced by 10 to 16 per cent. A control method of this type would have many advantages. Much crop damage is caused by concentrations of large numbers of young birds, and if hatching success were reduced there would be fewer of these. Adult birds would remain to defend their territories and prevent surplus birds from surrounding districts moving into the “vacuum” that results from a re-

duction of bird population by poisoning, and the treatment could be stopped as soon as the population of the target species fell to an acceptable levpl. Much research remains to be done on drugs and methods: of application, however, and I it is likely to be several years before the technique is sufficiently developed for rout-: line use.