The Peregrine Fund posted the following information on the developing “chicks”. It is really some very interesting information. Enjoy.
Now more than two weeks old, the chicks are able to stand more erect. Their legs are not yet strong enough to hold them, but they can shuffle around the nest box on their haunches to explore their surroundings. In another week or so, they will be able to stand fully upright. This will be a relief to the adults because the chicks can then start feeding themselves, rather than relying on their parents to feed them every bite. At that point, both adults will shift into full-time hunting mode to provide enough food for their offspring, who are growing at lightning-fast speed.
The size difference between the chicks is likely due to gender. Males can be a third smaller than females, so they may never grow up to be as big or strong as their sisters. But they will be more agile in flight!