Corn is as nutritious for many birds as it is for humans. Many ground-feeding birds such as doves and native sparrows take cracked corn, and whole kernels are appreciated by ducks, geese, jays, crows, and cranes. A few birds will take corn off the cob, but normally squirrels beat them to that.
Platform feeders and tray feeders set just above ground level should have a screened bottom for drainage. Corn spoils very easily, and one type of bacteria that thrives on corn produces a dangerous toxin, so only offer as much as your birds will consume in a day or two. If corn does get moldy, it should be thrown away or composted where birds cannot get to it.