Why do wild birds throw most of the seeds out of the feeder?

Question

I watch the birds as they are eating the seeds and they just throw the seed out with their beaks. I thought it may be to feed other birds below or maybe they just don't like those seeds. Any ideas???

Answer 1

They don't "throw them out"; they peck at them and eat the ones they like and as they're pecking at them - the others fall out - get knocked out.

Answer 2

They are trying to throw out the chaff, or empty husks of already consumed seeds.  Some seed will be thrown out with the chaff.  Ground eating birds will take advantage of this, so it looks like the song birds are feeding the doves.