Update 5/9: Much fluttering about, and some tentative flying today. In the morning, one of the birds made this little journey:
I'm not really sure where he went; he might have left the nest, or he might have just flown off to the left. But he was gone for about a minute.
Later in the afternoon, another flight. Again, I'm not really sure how extensive this one was, but he was gone for about five minutes. Here we see him leaning on the rail, getting ready to launch. The other bird is just barely visible behind him.
While that bird was away, the other one tested his wings, and was able to lift himself out of the nest briefly. He didn't leave, he just took off and landed in the same spot a few seconds later.
