Conservation introductions, the intentional movement of species’ outside their natural range to achieve a conservation goal (Seddon et al. 2014), are becoming an increasingly relevant strategy to help restore, maintain, and protect biodiversity in a changing world. Most conservation introductions focus on a target species, often at risk of extinction, and identify habitat for introduction. We consider a novel, inverse scenario in which a species endemic to an island has gone extinct, and the drivers of its extinction has been removed, creating habitat into which a population of a closely related species could be introduced. Island species are among the most threatened taxa globally, and this proactive conservation approach may not only benefit the island's ecosystems and values, but also provide an additional insurance population for the source species. Where an extinct species has multiple closely related extant species, a decision must be made about which source population to consider for a conservation introduction. We undertook a structured decision-making process to identify an optimal source population.