Can Barn Owl (Tyto furcata) Nest Boxes in Winegrape Vineyards Sustain a Population of Barn Owls?

Controlling small mammal pests and their damage has always been a challenge for farmers. Farmers and researchers worldwide have been experimenting with deploying nest boxes to attract barn owls to their fields to remove rodent pests. While much research has focused on the potential for nest boxes and barn owls to benefit agriculture, comparatively little work has examined the impact of the practice on owls. In this study, we used a life table analysis and estimates of barn owl reproduction measured in winegrape vineyards in Napa Valley, California coupled with published estimates of survival from long-term studies in Europe to produce a demographic model of a population of barn owls using nest boxes. We then examined how manual perturbations of survival and reproductive rates affect whether the modeled population is stable, increasing, or decreasing. Based on our empirical estimate of reproductive success and literature-sourced estimates of survival, the population appears to be growing. Across all scenarios in which we adjusted survival, there were only five that resulted in the population declining. All scenarios that resulted in population decline occurred when survival was reduced for all ages simultaneously or for adult survival independently. There were no scenarios in which lambda dropped below 1 when modifying reproductive success independent of survival. These results are important for practical pest-management reasons, as nest boxes cannot be part of a successful long-term integrated pest management (IPM) plan if they are reliant on continual immigration of adult owls from other source populations to offset mortality. A thorough examination of ecological traps should be conducted using additional information on habitat selection and reproduction in natural nest sites