The large-scale management of Barred Owls (Strix varia) in northern California has provided a unique opportunity to investigate wildlife exposure to rodenticides across a broad landscape. Liver samples collected from hundreds (n = 765) of Barred Owls reveal that nearly half (46%) show evidence of rodenticide exposure—mostly anticoagulant rodenticides (ARs), including 36% with second-generation ARs banned for use in California since 2020. These results highlight the ongoing contamination risk but also raise a key question: Are owls acquiring these pesticides directly through prey consumption, or indirectly through maternal transfer reflecting legacy exposure? To resolve this, we focused on subadult age classes and refined age along a continuum based on owl removal dates, molt phenology, and hatch dates. This approach allowed us to assign “precise” ages between 5.5 and 12.5 months and provided the resolution needed to detect exposure patterns that were not resolvable with coarse age classes. The resulting age-exposure relationship supports prey-based accumulation rather than natal transfer, indicating that banned ARs persist in local food webs 5 years post-regulatory ban. By refining aging methods, we provide a framework for precisely aging individuals and distinguishing natal from environmental exposure.