Multi-scale analysis of barn owl nest box selection on Napa Valley vineyards

Abstract

Abstract Barn owls ( Tyto alba ) have the potential to remove significant numbers of rodent pests in vineyards, which has prompted viticulturists in California to erect artificial nest boxes to attract owls. This study examined the habitat factors influencing barn owl nest box occupancy as well as farmers’ perceptions of barn owls in vineyards in Napa Valley, CA. Nest boxes of variable design and placement were distributed across 65 vineyards that varied in local and landscape habitat composition. We monitored 297 nest boxes in 2015 to develop an occupancy model. We evaluated the performance of the 2015 model by revisiting 150 boxes in 2016 and comparing observed occupancy to the predicted probability of occupancy for each nest box. Barn owls occupied approximately one third of the nest boxes we monitored each year. We used variance decomposition to address cross scale correlations among three nested spatial scales and to analyze the variation in nest box occupancy explained uniquely by predictors at each spatial scale. The home range and nest box scales were the most important spatial scales. At the home range scale, barn owls selected nest boxes surrounded by more hectares of grassland, riparian and mixed forest, and fewer hectares of oak scrub within 1 km of the box. Owls were more likely to occupy nest boxes if they were constructed of wood, facing north and positioned higher off the ground. The model developed in 2015 performed well in 2016, correctly classifying 81.3% of the boxes, and the area under the receiver operating characteristic curve was 0.86. In addition, we surveyed farmers to gauge their perceptions of the utility of barn owls as a component of an integrated pest management scheme in winegrape vineyards. The majority of farmers surveyed installed barn owl nest boxes for the perceived pest management services instead of the potential positive public appeal of improving barn owl habitat.