Barn owls are one of the most widely affected species by secondary poisoning from rodenticides, with over 90% of tested individuals showing exposure to second-generation anticoagulant rodenticides.
Barn owls are acutely vulnerable to secondary rodenticide poisoning because they are highly specialized vole and mouse predators. SGARs including bromadiolone, brodifacoum, and difenacoum persist in rodent tissue for weeks after lethal ingestion. Owls consuming multiple poisoned rodents accumulate lethal doses. Affected owls show weakness, inability to fly, uncoordinated movement, and eventually die from internal hemorrhage. Post-mortem studies consistently find SGAR at toxic concentrations in barn owls across the UK. Even sub-lethal exposure impairs immune function, breeding success, and survival. First-generation rodenticides including warfarin are less accumulative but are resistant-proof concerns limit their use. Physical rodent control methods including trapping and proofing can substitute for rodenticides.