After only a few minutes, a chickadee flew to the edge of the hole, and perched.
Then, it entered the hole, and all I could see was its tail.
After a few minutes, the bird peered out of the hole...
and took flight.
But, either it, or its spouse returned shortly. I didn't get a shot of them entering the nest hole (I was battling some wind blowing the boat around a bit), but my suspicions of chicks in a nest were confirmed with the appearance of the parent with a fecal sac.
Birds keep their nests very clean and remove the fecal sacs of the chicks, who poop after being fed.
Up, up and away goes the fecal sac! (Gee...the world does revolve around poop, doesn't it!)