The chemical frightening agent 4-aminopyridine (4-AP) has been repeatedly tested as a means of protecting both ripening corn (De Grazio et al. 1971, 1972; Besser et al. 1973; Besser 1976; Dolbeer et al. 1976; Stickley et al. 1972, 1976; Woronecki et al. 1979) and sunflower (Besser and Guarino 1976; Besser and Pfeifer 1978; Henne et al. 1979; Besser et al. in press) from depredating blackbirds. It was reported that less than one percent of a flock need ingest the treated baits and respond with distress symptoms in order to move birds from a corn field (De Grazio et al. 1972) or even shift roosting aggregations from night roosts (Cummings 1979). However, there is still conflicting evidence as to whether frightened blackbirds will subsequently avoid nearby fields, or even the same treated fields, resulting in efficient protection. The efficacy of 4-AP has not been resolved because of questions about the presentation and formulation of the treated baits and the difficulty of conducting a valid, unambiguous field test. This study was a large-scale evaluation of AvitroⓇ (HCI) FC-Corn Chops-99S1, where all commercial sunflower fields were monitored within a 144-sq mi block centered around a major concentration of roosting blackbirds; and all those fields with significant bird pressure were baited. The test was designed to answer two questions: can selective baiting (1) reduce damage overall when compared with pre-treatment damage from 1981, and (2) disperse it within the block? In other words, can the treatment keep blackbirds out of preferred fields? If so, is the result an overall reduction in damage within the surrounding area, or is it a redistribution of the damage
