I had the same problem with ravens here, when I used leaves to mulch the garlic. They didn't damage the plants at all though, but they were tearing up the mulch to go after insects underneath. This year I pre-empted their frolics by removing the leaves myself.
I've seen the problem before with young transplants, that the birds would pick them out and fling em as they're looking for bugs or worms. I find it safer to cover the beds until transplants have rooted in, before letting them go about their buggy business.