MH LoCAThe LWC is in its third year of successful collaboration with Mark Browning and PG&E to research and promote the use of barn owls to control rodents in Lodi vineyards. In January, the Research and Education Committee voted to fund Browning’s third year of data collection from research sites in Vino Farms vineyards. The research is comprehensive and will look at Lodi vineyards carrying capacity for barn owls, optimum nest box density per acre, preferred nest box orientation, the general period of barn owl breeding season, hunting behaviors, and their preferred prey. Most interesting, Browning will track the relationship between changes in prey population and barn owl population. Such insights will advance our understanding of how barn owls can be used to successfully control vertebrate pests in vineyards. For readers interested in learning more about the study, see the February 2011[1] and April 2013[2] editions of Ag Alert.

Browning’s results from 2011 and 2012 data are encouraging. In the first year, 55% of the nest boxes were occupied and occupancy rose to 75% in the second year. The 24 nest boxes included in the study resulted in 11 mating pairs and 40 fledged young in the first year and 18 mating pairs and 66 fledged young in the second year. Browning also found a negative correlation between barn owl numbers and rodent numbers, which is a strong argument for the effectiveness of barn owls for rodent control. Pellet analysis revealed that 83% of barn owl diets are comprised of pocket gophers. Browning’s research also found that barn owls prefer nest boxes facing easterly directions.

PG&E’s Owl Safe program has had a significant impact on the number of barn owl nest boxes in Lodi vineyards. Since 2011, PG&E has donated $60,000.00 toward making next boxes available to Lodi growers free of charge. As a result, a total of 257 nest boxes have been distributed. Given Browning’s research findings, it is likely that PG&E’s Owl Safe program has indeed had a positive effect on rodent control in Lodi vineyards.

To help Lodi growers get the most out of their barn owl nest boxes, the LWC has authored a leaflet on barn owl nest box best management practices. The leaflet, Barn Owl Nest Boxes: Best Management Practices, summarizes information from a number of scientific resources about next box site selection, installation, and maintenance. The leaflet is free to all Crush District 11 growers and is available by contacting the LWC.

[1] Adler. 2011. “Farmers provide homes for owl that control pests.” Ag Alert.

[2] Alder. 2013. “Project tests owls’ success against vineyard rodents.” Ag Alert.