Banding records of nestling barn owls reveal optimal timing for nest box maintenance in California

Abstract

American barn owls (Tyto furcata) often rely on nest box networks for breeding, especially within agricultural landscapes. Nest boxes are commonly installed for pest management purposes and require regular maintenance, such as removal of pellet debris and repairs, to remain functional and safe for breeding owls. Ideally, nest box maintenance should be conducted before the breeding season begins to minimize nest disturbance. The timing of the barn owl breeding season is especially important to understand in California, USA, which has a high diversity of ecoregions and expansive latitudinal range. Our objective was to describe the barn owl breeding season throughout California using nestling records to assist with data‐driven management recommendations. We queried 96 years of barn owl nestling banding records (n = 22,670) from the United States Geological Survey Bird Banding Lab to estimate egg laying dates across California and summarized 39 years of intake records (n = 1,741) from the California Raptor Center in the Central Valley. Our results suggest that barn owls typically begin to lay eggs in California in winter months; the median egg laying date for the state was 20 February. Based on these reports, planning for barn owl nest box maintenance to begin in fall (Sep–Nov) would align with the season that breeding activity and nest disturbance may be lowest, especially in the Central Valley and Southern Coast ecoregions.