Effective line installation technique for preventing crow intrusion into orchards

Abstract

For protecting crops, scaring devices have only limited effect to deter birds because of habituation. Installation of lines over the crops has some effectiveness as persistent physical barrier against birds. However, the effectiveness of lines differs among the bird species and environment of the sites concerned. In this study, we aimed to develop a simple and effective line installation technique as a means of preventing crow damage in orchards. From the experiments on captive crows, stringing transparent nylon lines in parallel at 1-m intervals, which is equivalent to wingspan length of the crows, was effective in suppressing intrusions. Transparent nylon lines were more effective in preventing crow intrusions than colored highly visible wires. For crows, line-shaped obstacles with low visibility were suggested to be effective barriers for preventing their flight into the places. Based on these results, we devised a method for stringing nylon fishing lines at 1-m intervals across an orchard with its sides covered by netting. The experiment to evaluate the effectiveness of this method on wild crows indicated that it would be effective enough in controlling crow intrusion to put to practical use in orchards.