Not Swallows, then what Birds?

What are these two black birds doing on the roof of the Swallow House?
Swallow has scissor tail, these birds do not have.
Are they preying on the swallows ? No, they are too small.
Are they feeling threatened, each one guarding at different directions? Yes, there is a hawk around, circling in the sky.
Are they starlings ? Do not look like, cannot see the red eyes, the feather does not seem glazed and greenish.