Violet-green Swallow

I took this photo of a male Violet-green Swallow in our backyard this afternoon.  The color at the base of his rump and tail I presume is violet, which I also am presuming accounts for the name of this swallow. Its not always easy to see this violet patch, and as a matter of fact I don't recall before this year being aware of it's existence. This particular male is standing daily on guard over a nearby nesting box currently occupied by a female.  This afternoon we got to see him in action when a pair of lousy House Sparrows made a failed attempt to enter the nesting box.  He was on them immediately, and chased them away.  He appears to be at his leisure standing by, but we learned today he is actually always on the alert.