Facing the dilemma at eradication's end: uncertainty of absence and the Lazarus effect

Feral ungulates, such as pigs, are highly destructive to island ecosystems and are therefore often the target of eradication efforts. To succeed in eradication, however, managers must address a question made formidable by the great difficulty of detecting animals at very low levels of abundance: how will we know when elimination has been achieved? We developed and tested a framework to address this problem in a program to remove feral pigs from Santa Cruz Island, California. In an unprecedented timeframe for an island of this size, the program has progressed to a point at which pigs can no longer be detected. We describe seven key attributes of our approach, and how they have increased the likelihood that our inability to detect additional pigs indicates successful eradication, rather than the pigs having become better at escaping detection. This approach represents an important advance in the practice of eradication that can serve as a model for increasing the pace and scale of island restoration around the world.