Is this bird being a bully?

Sorry for the bad pictures anytime I try get closer it's gone. This bird is about the size of a robin, black with white dots. NE Ohio.

It seems to be bullying the birds that live in my little bird house. It's always sticking its head in the holes and sitting on the roof all puffed out. I'm afraid it's gonna hurt the babies this spring.

There are plenty of resources for all the birds. I don't know why this one seems so set on picking on the smaller birds. Is it just being a bully?