Bologna

16 days old are these two and watch them excersising their wings. It is a kind of body building their flapping their wings.
We all know that without a daily work-put our muscles will stay small. For these fledgelings to be it's very important they train their major flightmuscles before they can take off in 3-4 weeks.
The flight muscles pectoralis & supracoracoideus are very large & located near the center of gravity: pectoralis or downstroke muscle - originates on the keel and inserts on the underside of the humerus.
The supracoracoideus or upstroke muscle - originates on the keel and inserts on the upper side of the humerus,
The last one is very important and is not strong enough by the time they fledge. Most fledgelings can not manage to ascend again once on the ground. There is the major danger with fledgelings. Only a few are able to gain hight once down.
So this wingflapping is getting stronger and preparing for first flight. There are eyases who start very early, like the Rome eyases.