Effects of habitat on prey delivery rate and prey species composition of breeding barn owls in winegrape vineyards

Abstract

The provision of habitat for natural enemies of agricultural pests is common in integrated pest management approaches but has rarely been examined for vertebrate predators controlling vertebrate pests. To mitigate the economic and environmental costs of removing rodent pests in vineyards in Napa Valley, California, winegrape producers have installed nest boxes to attract American barn owls (Tyto furcata) to their properties. A rigorous estimate of how many rodents barn owls remove from the landscape is a necessary first step to understanding the overall impact of barn owls on rodent pest populations, and this study provides an estimate of rodent removal and prey composition by using remote nest box cameras. In addition, we tested hypotheses for how habitat may influence prey delivery rates and composition. Videography indicated that each barn owl chick received on average of 191 ± 10.01 prey items before fledging the nest box and that the amount of grassland habitat near the nest box and the proportion of deliveries of smaller prey were positive predictors of prey delivery rate. Prey composition was dominated by voles, gophers, and mice, and their relative proportions were associated with the composition of habitats near a nest box. Specifically, oak savannah was positively associated with the proportion of gophers and negatively associated with voles, and grassland was positively associated with voles. Further research on prey delivery should focus on the possible roles of rodent abundance, adult owl quality, and additional metrics of habitat structure.