This is either a small wasp or a native species of solitary bee. It wouldn't come out where I could get a good look at it. The nest is roughtly 1.5 inches from top to bottom and appears to be used over again every year. Just a day or two after I took this photo, all three holes were sealed back up again.

When I first spotted it, there was something else moving around near the opening (possibly a larva?) and a faint high-pitched buzzing was coming from the nest - Mom fanning her wings to cool the place down a bit? When I got back with the camera, the buzzing had stopped and there was just the one critter looking out the hole.

I took a flash photo of this too, but it didn't come out as clear as this one.

Ever since I took this shot, the old Beatles song "I've Just Seen A Face" has been bouncing around in my head.