Interspecific introgression increases genetic diversity and reduces genetic load in red kites

Introgression from the black kite (Milvus migrans) is linked to an 18% increase in genetic diversity in the northernmost red kites (Milvus milvus).

• Why it matters: Severe declines can erode genetic diversity and leave populations vulnerable even after numbers rebound, but it is unclear whether gene flow benefits outweigh outbreeding costs as divergence rises.
• What they did: Using genomic data, the study inferred long-term small population size, very low genetic diversity, moderate range-wide inbreeding, and substantial recent inbreeding, then linked northeastern diversity patterns to black kite introgression.
• The result: The introgression decreased realized genetic load and increased diversity in northernmost red kites by 18%, suggesting differentiated sister species can refuel diversity and alleviate load.