a little research indicates this "wolf-whistle" call is not that uncommon, though it's certainly new to me and possibly new to these particular birds. i also discovered that the longest known lifespan of a member of this species is about 15 years, and that it's altogether common for them to return to the same nest year after year. according to wikipedia, these birds can be either monogamous or polygamous, so it's at least possible that only one of the birds (i would guess the male) is returning year after year. i've always assumed they must be migratory, since i don't see them all winter, and it turns out they are, when born in sufficiently northern latitudes.
i was starting to wonder if they'd make it back this year, and i'm somewhat surprised by how happy i am to see them. welcome home, old friends.
classic pose
up from the front yard, looking for something to eat
cautious
coming down to the edge of the garage roof to have a look at me through the window- and wait for me to leave before entering the nest.