Someone said that the Fireworks might have done it.
Ummmm, unless I’m sadly mistaken - Blackbirds do not fly at night. They like to see where they are flying. We don’t launch a whole lot of Fireworks until night falls and it is pretty dark out there.
What if they’re migrating? Up here in the mitten, some of our best chances at seeing migrating birds (both coming and going) are early evening, as they set out, and mid-morning, as they’re looking for a place to roost for the day. I know Red-wing Blackbirds are migratory—I sure do miss them this time of year.