Examining barn owl nest box selection at three spatial scales on Napa Valley vineyards

Barn owls (Tyto alba) have the potential to provide rodent pest removal services in vineyards, which has prompted viticulturists in California to erect artificial nest boxes to attract owls, but this system has not yet been rigorously researched. This study examined the factors influencing nest box occupancy. I monitored 297 nest boxes in Napa Valley, CA during the spring of 2015. Nest boxes of variable design and placement were distributed across 65 vineyards that varied in local and landscape habitat composition. Barn owls occupied 92 of the nest boxes for breeding. I used variance decomposition to address cross scale correlations among three nested spatial scales and to analyze the variation in nest box occupancy explained by predictors at each spatial scale. The full model explained 41% of the variation in nest box occupancy. The home range and nest box scales explained the majority of the variance in nest box occupancy. 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. Placing well-designed nest boxes in optimal habitat can boost nest box occupancy rates, which may help farmers reduce rodent pests and increase regional barn owl populations.