Deliberately introduced them...
Probably the same moron who introduced Kudzu, the Water Lilly, Fire Ants, the Sea Lamprey, Zebra Mussels, etc etc etc.
Dang things won't speak English either. Bet they simply want to ruin our way of life. We'd better'd put a fence around our border like the Israelis are doing.
Starlings (and house sparrows) were actually introduced in the 1800's in NY's Central Park by some English asshat who wanted to bring to America all the birds mentioned in Shakespeare's plays. Nice work, Lord Half-a-Head.