a murder of crows

There is a young robin that keeps me company while I am gardening. I guess it hopes I will turn up something good to eat, as often I do. It doesn't seem afraid of me.
    The other morning I heard a redwing blackbird screaming alarm. I thought it was the hawks or egrets after their nest again, and started outside to scare them away. The redwing blackbirds are pretty good at it on their own—a single brave little bird or sometimes a team gives chase. But instead I chased off a murder of crows on the back porch that were tearing apart a little bird.
     I could hardly look at the poor thing. That robin was too trusting, I thought.
     But it wasn't "my" robin, because later, when I went out to dig, there it was, hopping around.