Potential for Barn Owl as Rodent Biological Control in Central California Vineyards

The pocket gopher (Thomomys bottae) and voles (Microtus spp.) cause significant economic damage to vineyards. In response, many growers have taken steps to attract Barn Owls (Tyto alba) to their properties to help keep these rodent populations in check. This research project investigated Barn Owl consumption of pocket gophers and voles in Central California vineyards in order to assess the efficiency of this integrated pest management strategy. I collected a total of 715 owl pellets from five vineyard locations in Templeton and Paso Robles, California over an eight-month period during nesting and post-fledging seasons. I identified seven prey species within in the owl pellets, allowing for comparative analysis between the two collection periods. Comparisons of the average number of individuals per species per pellet (AVG) and a paired t-test indicated seasonal diets of Barn Owls are statistically similar. Although there was slight variation in AVG values between seasons, this research did satisfy the expectation that the diets from each vineyard would contain similar percentages of gopher and vole species. Microtus was the most highly consumed prey genus and made up the majority of both the spring (AVG = 0.528) and summer diets (AVG = 0.599) with a p-value of 0.77. Seasonal consumption for gophers was statistically similar and Thomomys bottae was the second most highly consumed prey species behind Microtus californicus, with AVG values of 0.304 (spring) and 0.299 (summer) with a p-value of 0.80. It would be fair to conclude from this snapshot of seasonal consumption that Barn Owls consume important vineyard pests and have the potential to assist in regulating these rodent populations.