Bird Problems in agriculture

Abstract

British Crop Protection Council Publications. 210 pp. oe10.00.-Man has encountered problems with bird "pests" for as long as he has practiced agriculture. The usual solution has been to kill the birds if possible , or to attempt to scare them elsewhere. This volume contains a series of papers delivered at a symposium held in 1977 under the auspices of the British Crop Protection Council, which had the specific aim of stimulating interest in seeking new approaches to the control of bird damage to agriculture. The articles are organized into four general sections, each containing a chairman's introduction, four contributed chapters, and a few pages of general discussion. The first section addresses general considerations of pest birds and agriculture. A common theme runs through this and the following section: the birds that assume "pest" status are generally predisposed to do so, as their adaptive features combine with alterations imposed by man upon their habitats to bring their use of habitats into conflict with that by man. In some cases, the problems are a consequence of the sheer numbers of birds involved, and Moore suggests that in such situations the pest populations could be reduced "without detriment," so long as the control measures were specific to the pest species. But often it is winter flocks of relatively rare species or small numbers of breeding individuals that cause the most severe damage, at least on a local scale. Flegg, for example, points out the devastating effect that a "handful of bullfinches" can have upon pear orchards by stripping buds from the trees. All of this suggests that control of the bird populations may not be the most practical solution, and that it may be more effective to control instead the patterns of agricultural cropping practiced in areas sensitive to bird damage, or simply to compensate farmers who suffer severe local damages (as Boyd discusses). The second section specifically addresses the problems posed by Starlings as agricultural pests, and continues the themes established in the first section. Two chapters review in some detail features of the breeding systems of Starlings and the features that contribute to their high reproductive output (Ver-heyen) and the tactics that are employed by Starlings in foraging (Tinbergen and Drent). The latter chapter is especially lucid, and, when coupled with Tinber-gen's recent detailed report on this research (1981, Ardea 69: 1), provides an excellent view of the sorts of factors that contribute to the pesthood of Starlings. Aspects of the economics of Starling damage are reviewed by Feare, who notes that (a) the problems caused by their consumption of cherries in orchards may at least partly be a consequence of the inability of farmers to regulate the number of cherry pickers in relation to the amount of ripening fruit, (b) despite the damage to germinating cereals close to winter roosts, there is no evidence that this has a significant effect on crop yield, and (c) good evidence that Starlings are involved in disease transmission is lacking. Thus, despite the conspicuousness of Starlings in agricultural areas, the magnitude of their real economic effect (if any) is not well established. Nonetheless, Starlings are the subject of some of the more spectacular control measures, such as the massive efforts to dynamite roosts described by Tahon. As with so many control programs of this sort, this has not had much success: "The promoters of the use of explosives predicted a severe reduction in the starling population after one year, so that it should have been possible after some time to limit or to stop roost destruction. But from the start, it was evident to biologists that a 5 to 20% reduction of the population was insufficient to gain such a result. Evidence of that misjudgement is provided by the relatively stable number of birds killed each year in a population which is still approximately at the same level as be-fore" (p. 67). This is largely a consequence of the movement patterns of the Starlings, and Tahon emphasizes the critical role of banding studies in defining these movement patterns and (in this case) in showing why such control is unlikely to be effective. As Feare notes, "a more practical alternative may well be to regard a bird pest simply as another environmental factor that must be taken into account when considering modifications to existing husban-dry techniques or the introduction of new ones" (p. 52). The last two sections deal with two alternative control measures, scaring the birds and using chemical repellents. The treatments of bird scaring consider the interplay between basic features of bird behavior, such as habituation, and various scaring techniques. Several of the authors observe that scaring is generally founded upon the assumption that novelty repelIs birds, but that in order to have any real prospects for success, scaring techniques must be built upon a deeper knowledge of the behavior of pest birds, as most scaring approaches have met with limited success at best. The treatments of chemical repellents likewise stress the importance of a full knowledge of the behavior of the birds as a prerequisite to implementation of avian repellents.