Genomic erosion across avifauna in a biodiversity hotspot sounds a conservation alarm

Loss of biodiversity can have a hidden dimension-the cryptic erosion of genetic diversity even in the face of apparent species resilience. We quantified changes in genetic diversity by comparing historical and modern genomes of 62 songbird species from the Gaoligong Mountains, a biodiversity hotspot in southwestern China. We identified genomic loss averaging between 43 and 49%; and, unexpectedly, common species were disproportionately affected. We argue that this loss was driven primarily by habitat fragmentation (and mitigated by dispersal ability) and show that it exceeds prior estimates and conservation policy thresholds. Species identified as having lost diversity continue to be listed as "Least Concern" on the International Union for Conservation of Nature's Red List of Threatened Species, exposing a blind spot in extinction risk monitoring. We call for genomic metrics to be rapidly integrated into global conservation frameworks.