Proceedings of the Vertebrate Pest Conference

Several rodent species cause damage in vineyards and orchards. Current efforts to reduce chemicals used to control rodents are encouraging development of alternative practices, such as biological control. For several years growers in California have been installing artificial owl nest boxes to attract barn owls with the hope of reducing rodents, especially gophers, through predation. Effectiveness of barn owls as biological control of gophers in vineyards and orchards is unknown. The purpose of the study was to use growers surveys and diet analysis to assess the effectiveness of installing barn owl nest boxes to control gophers. Surveys of growers that installed artificial nest boxes reported that 40% of boxes were occupied within six months of installation. Of those growers with occupied nest boxes, however, only 23% felt that barn owls were effective in controlling gophers on their lands. The diet results indicated that barn owls most frequently prey upon gophers and voles. Barn owls prey upon both adult and juvenile gophers, and juvenile gophers were especially vulnerable during spring and summer. The findings provide little evidence that barn owls are effective in controlling gophers. With further research the approach might prove useful, but only when used in concert with other control approaches such as trapping and rodenticides.