Islands are at the frontline of the anthropogenic extinction crisis . A vast number of island birds have gone extinct since human colonization , and an important proportion is currently threatened with extinction . While the number of lost or threatened avian species has often been quantified , the macroevolutionary consequences of human impact on island biodiversity have rarely been measured . Here, we estimate the amount of evolutionary time that has been lost or is under threat due to anthropogenic activity in a classic example, New Zealand. Half of its bird taxa have gone extinct since humans arrived [6, 7] and many are threatened , including lineages forming highly distinct branches in the avian tree of life [9-11]. Using paleontological and ancient DNA information, we compiled a dated phylogenetic dataset for New Zealand's terrestrial avifauna. We extend the method DAISIE developed for island biogeography  to allow for the fact that many of New Zealand's birds are evolutionarily isolated and use it to estimate natural rates of speciation, extinction, and colonization. Simulating under a range of human-induced extinction scenarios, we find that it would take approximately 50 million years (Ma) to recover the number of species lost since human colonization of New Zealand and up to 10 Ma to return to today's species numbers if currently threatened species go extinct. This study puts into macroevolutionary perspective the impact of humans in an isolated fauna and reveals how conservation decisions we take today will have repercussions for millions of years.