When Absence of Evidence Is Not Evidence of Absence: What an Advanced Case Reveals about Plastic Impacts on Seabirds.

Plastic pollution is a pervasive global threat, yet population-level impacts on wildlife remain poorly resolved for most taxa. Sable Shearwaters () offer a rare opportunity, exhibiting some of the highest documented plastic burdens of any seabird and demonstrating clear physiological and demographic harm even at low exposure levels. Their case reveals that the widespread assumption of minimal plastic impact is largely founded on a lack of evidence rather than evidence of no effect, driven by the difficulty of detecting mortality and sublethal effects in complex marine systems. Their shared life history and anatomical traits make their responses to plastics broadly indicative of what many species may experience as global plastic inputs continue to rise. As international policy efforts stall, these findings highlight the urgency of anticipatory, rather than reactive, research and governance. Extreme-exposure systems like Sable Shearwaters provide essential early warning signals that must inform rapid conservation and regulatory action.