Date of this Version
Proceedings Ninth Bird Control Seminar, Bowling Green, OH. Oct. 4-6, 1983.
In Switzerland, carrion crows can cause considerable damage to sprouting corn fields when feeding on the germinated corn. I tried to evaluate a method to prevent these damages. The use of species-specific distress calls, for the first time described by Frings and Jumber (1954), seemed to be the most promising method. Agronomes and biologists have applied it in field studies to several different bird species causing damage in agriculture and on airports (e.g., Gramet, 1962; Brough, 1968). However, the literature either describes single actions or several different scaring devices being used together. To be able to judge the method, quantitative information about reduction of damage, habituation, and some practical information about the construction of an effective apparatus was needed.
Distress calls proved to be a very effective method to keep carrion crows from sprouting corn fields, while suspended bodies of dead crows had no scaring effect. With distress calls, the chosen intervals of 25 minutes with 20-30 seconds broadcasting proved to be appropriate.
Among the factors influencing crow damage on corn fields, the most important was extreme wetness. Another factor of importance was the date of sprouting of the plants. A possible reason for this is that earlier in the year crows find less food, which causes them to search the ground and forage on all possible sources; open arable land is frequently visited as it offers much insect food.