A 150‐Year Avian Extinction Debt Forewarns a Global Species Crisis and Highlights Conservation Opportunities

ABSTRACT Humans have caused pervasive wildlife habitat loss by transforming most of the Earth's terrestrial surface, while unexpectedly limited species have consequently gone extinct. The concept of time‐lagged extinction (i.e., an extinction debt) potentially explains this paradox, but the starting time of the process is difficult to estimate. Herein, by projecting extinction risk backward onto human perturbation time series, we applied a statistical framework to examine extinction debt for 8435 terrestrial avian species. The results suggested that the modern extinction risk induced by anthropogenic terrestrial land modification began 150 years ago, aligning with the acceleration of human activities since the Second Industrial Revolution. Intriguingly, we found a reversal of anthropogenic effects on extinction risk over the mid‐20th century, perhaps driven by spatiotemporal contrasts in anthropogenic perturbations between developed and developing areas. These findings indicate the need for proactive conservation and highlight the role of ecosystem restoration in the potential repayment of extinction debt.