The arrival of D1.1 could signify a turning point in the H5N1 outbreak. Over December and January, owners of commercial, backyard, and hobbyist chicken flocks had to cull 41.4 million birds because of influenza exposure—three times more than the same period last year. The past two months are the most destructive stretch of the North American outbreak, which initially arrived three years ago via migrating wild birds from Europe.