Guinea pig pellets are actually made of hay, fortified with vitamins and minerals. I wonder if a bird actually could eat them, or would like them. I suspect not, though.
We did actually buy a big bag of bird seed at one point for making home-made bird feeders. Unfortunately the seed was infested with weevils, which spread into our kitchen and destroyed a lot of our food. So I'm not really a big fan of keeping bird seed around any more.