Comparative Effectiveness of Avitrol, Exploders, and Hawk-Kites in Reducing Blackbird Damage to Corn

Abstract

The ability of chemical (Avitrol FC-99), auditory (propane exploders), and visual (hawk-kites) stimuli to reduce bird damage to field corn was compared. In unprotected fields, birds destroyed an average of 1,587 kg of grain/ha, reducing yield by 22%. Avitrol FC-99 was the least successful and was not costeffective. Exploders reduced bird damage by 77% and were the most cost-effective of the three techniques, with a cost : benefit ratio of 6.1:1. Hawk-kites reduced bird damage by 83% and had a cost : benefit ratio of 3.5:1. Most of their cost was associated with maintaining the helium balloons used to keep the kites aloft. J. WILDL. MANAGE. 48(1):109-1 16 Red-winged blackbirds (Agelaius phoeniceus) and common grackles (Quiscalus quiscula) can cause extensive damage to ripening cornfields. In a single year, losses were estimated to be $1,400,000 in Pennsylvania (Wakely and Mitchell 1981), $6,780,000 in Ohio, $1,360,000 in Michigan, $1,200,000 in Kentucky, and $380,000 in Tennessee (Stickley et al. 1979). While representing less than 1% of the total value of the corn crop in these states, such damage is usually concentrated, with a small percentage of the farms suffering losses of over 10% (Dolbeer 1981). Farmers often use one of two different techniques to reduce bird damage: propane exploders or a chemical, 4-aminopyridine (Avitrol FC-99). The latter produces erratic behavior and vocalizations in birds consuming it, and their behavior is supposed to frighten away other birds. There is little reliable information on the efficacy or cost-effectiveness of these two techniques because rigorous tests are difficult to design and conduct. DeGrazio et al. (1971, 1972) and Stickley et al. (1976) conducted cost : benefit analysis of 4-aminopyridine in test areas where all or most of the fields were treated with the chemical. They obtained generally favorable results but, as Dolbeer (1981) observed, these studies did not evaluate the treatment form (Avitrol FC-99) registered by the U.S. Environmental Protection Agency (EPA) or its use in individual fields under commercial conditions. Moreover, other studies that have evaluated Avitrol FC-99 obtained mixed results (Stickley et al. 1976, Woronecki et al. 1979). Comparative data on different types of bird control techniques are usually not available. One exception is Stickley et al. (1972), who reported that bird damage to field corn was reduced 56% by 4-aminopyridine and 81% by propane exploders. In these tests, however, the chemical was applied at a rate four-five times higher than that later registered by the EPA. Hawk-kite predator models are another promising bird control technique. These are flown over fields by suspending them from helium balloons (Conover 1979). This method has successfully reduced bird damage in blueberry fields (Conover 1982). Until now, hawk-kites have not been tested in cornfields. The high cost of materials and labor associated with these techniques makes more information on their effectiveness desirable. This study evaluated the effectiveness of Avitrol FC99, propane exploders, and hawk-kites in J. Wildl. Manage. 48(1):1984 109 This content downloaded from 157.55.39.180 on Mon, 25 Apr 2016 06:15:49 UTC All use subject to http://about.jstor.org/terms 110 BIRD DAMAGE CONTROL * Conover protecting maturing cornfields from bird damage and provides cost:benefit analyses for these techniques. I thank W. G. Blasius, Jr., G. J. Bugbee, V. A. Connors, P. A. Halbert, B. A. McKinney, J. J. Perito, and D. E. Stone for help in data collection. D. E. Aylor, D. O. Conover, P. A. Halbert, and two anonymous reviewers helped improve earlier drafts of this manuscript. I especially thank J. J. Tiffany, II, and personnel at the Tiffany Farm for their cooperation.