Yep, those blackbirds are likely grackles...they can be nasty buggers and often travel in packs. If they come in numbers, they can really drive the seed bill up, too!
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."