At least I'm pretty sure this was his first attempt. It lasted about 30 seconds. It was a couple of days ago and he (she?) had only been standing up in the nest for a few days. A few hours before this there were some tentative wing exercises, but no evidence of any kind of coordination. I'd love to know if he was delighted or frightened -- he settled back into the nest (invisible in there as it's on a tall utility pole) for a long nap. Then a couple of hours later a little more uncoordinated flapping. Yesterday I saw no attempts at exercising.
Today a sibling was also standing near the edge of the nest, but no flapping while I was there. Light was not good this morning, but looks like it's improving this afternoon so I'm heading back out now. (I have my husband trained to drink beer until I get back to make dinner.)
Canon 7D2, 10-400 II at 400, f/6.3, ISO 800, 1/3200 sec. Very small adjustments in LR and into PS for crop and level -- this is the full frame height after a minor level. Cleaned some whitewash off the end of the beam and some very minor dodging and burning.