Bones of the flightless sea duck (Chendytes lawi) from 14 archaeological sites along the California coast indicate that humans hunted the species for at least 8,000 years before it was driven to extinction. Direct 14 C dates on Chendytes bones show that the duck was exploited on the southern California islands as early as Ϸ11,150 -10,280 calendar years B.P., and on the mainland by at least 8,500 calendar years B.P. The youngest direct date of 2,720 -2,350 calendar years B.P., combined with the absence of Chendytes bones from hundreds of late Holocene sites, suggests that the species was extinct by Ϸ2,400 years ago. Although the extinction of Chendytes clearly resulted from human overhunting, its demise raises questions about the Pleistocene overkill model, which suggests that megafauna were driven to extinction in a blitzkrieg fashion by Native Americans Ϸ13,000 years ago. That the extermination of Chendytes was so protracted and archaeologically visible suggests that, if the terminal Pleistocene megafauna extinctions were primarily the result of human exploitation, there should also be a long and readily detectable archaeological record of their demise. The brief window now attributed to the Clovis culture (Ϸ13,300 -12,900 B.P.) seems inconsistent with an overhunting event.flightless birds ͉ overhunting T he late Quaternary extinction of North America's large fauna has been a topic of intense scientific interest for decades, focused primarily on the Pleistocene overkill hypothesis, which suggests that 35 genera of megafauna were driven to extinction in a blitzkrieg fashion by Native Americans Ϸ13,000 years ago (1). This hypothesis has been challenged because of the paucity of supporting archaeological evidence for human hunting of most of the extinct taxa (2), while aspects of the extinctions have also been portrayed as inconsistent with climate change explanations (3). Added to this mix is a recent suggestion that an extraterrestrial impact Ϸ12,900 calendar years B.P. contributed to the megafauna extinctions (4). Here we challenge the overkill hypothesis based on the archaeological record of one of the few North American animals** demonstrably driven to extinction by Native Americans during the Holocene (6, 7)-the often overlooked flightless sea duck (Chendytes lawi).Flightless birds are evolutionary oddities that developed almost exclusively in settings without major populations of terrestrial predators. On many Pacific islands, archaeological findings show that flightless birds were highly vulnerable to human hunting and were quickly decimated soon after humans arrived (8, 9). On the North American mainland many species of birds last disappear from the fossil record near the end of the Pleistocene, but their demise cannot be confidently attributed to human overhunting because their remains are absent from terminal Pleistocene archaeological sites (10). Indeed, a longstanding problem with the overhunting hypothesis is the fact that most genera that went extinct during the late Pleistocene have never been foun...