Nasty little birds. We put out a feeder, and they battle each other for it, even when there's plenty for all. It's a good thing they don't decide to gang up on humans; they could do a lot of damage while we're still looking at where they were a hundred wingbeats ago.

I saw a hummingbird attack a squirrel once. Nasty indeed. I suspect the squirrel was getting a little too close to its nest.

Squirrels are cute, but they'll happily steal the eggs or hatchlings out of the nest if given the chance.

Different species, perhaps different groups within a species, behave differently. I've heard of this but never seen it.