There are two large black birds living in the canyon in back of my house. They occasionally swoop by the eaves looking for nesting pigeons. Sometimes I see them chasing the hawks and sometimes vice versa. They keep the house pigeon free like no human contraption ever did. I looked them up on the Internet and they appear to be Ravens, possibly Corvus corax. The give away is that sturdy hooked beak and the triangular point to the tail fan when they fly (as shown here). They claim that Ravens are more likely to frequent woods and open areas but these appear plenty happy in our little suburban canyon.