Farmers across Western North America have recently begun installing artificial nest boxes for Barn Owls and Kestrels, and artificial perches for hunting birds of prey in an effort to boost natural rodent pest control services. We conducted a survey of California farmers to measure their perceptions of birds of prey, conducted a diet study of nesting Barn Owls across multiple crop types to determine if diet changed across land use types, and used demographic and predator-prey models to quantify the effect of Barn Owls on rodent pests. However, because many farmers also utilize anticoagulant rodenticides to control rodent pests, raptors can suffer from both lethal and sub-lethal secondary poisoning. We have little understanding of how often raptors are exposed to rodenticides in an agricultural setting, especially at a sub-lethal level, and what effect this exposure has on their behavior and reproductive success. We have recently started a 3-year study in an intensive agricultural landscape in California to quantify the frequency and effects of secondary poisoning in Barn Owls breeding on farms.
Results/Conclusions
We found that over 95% of surveyed farmers believed that raptors were beneficial for vertebrate pest control, and over 56% of those surveyed believed that raptors were beneficial for crop yields. Our diet study results indicate that over 99% of Barn Owl diet in the region consists of agricultural pests and that the proportion of diet contributed by gophers and mice differs between predominantly row-crop and predominantly orchard/vineyard crop habitats. Our models reveal that in theory, barn owls are capable of keeping rodent populations below an environmental carrying capacity, and in some circumstances could drive pest populations to near-zero. Preliminary results show low rodenticide exposure in Barn Owls in winter at sites where rodenticides are applied near buildings (but not at the field-scale), and adds to existing diet data showing consumption of exclusively agricultural pests. At the time of submission, the barn owl breeding season in California is just starting, and 'late-breaking' results on rodenticide exposure will be presented on this poster.