DDT was widely used (and liked) because it was cheap and bro…

DDT was widely used (and liked) because it was cheap and broke down slowly in the environment. It targeted mosquitos, but they soon developed resistance factors and DDT became less effective. Birds however, are much slower to adapt/evolve and their numbers plummeted, and there was a ban on DDT in 1972 (in the US). How did DDT hurt the birds?