In autumn 2025, highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b virus, genotype EA-2024-DI.2.1, caused systemic infections leading to a mass mortality event among the western migrating subpopulation of Eurasian cranes (Grus grus) in Germany. Gregarious behavior at feeding and resting sites likely promoted rapid viral spread within the population.