I have been letting the chicks out in the morning to free range a bit while I do my livestock chores (so I can be there to deter hawks). They're just over 4 weeks old, and about 4 inches tall. My adult ducks, who rule the yard most of the time (chasing squirrels, bossing the cat), have been trying to chase the chicks around. But it doesn't happen. The chicks turn around and give it back to them, raring up and leaping at them. Turns the ducks on their tails--so funny to watch! It's not the size of the body that matters--only the size of the attitude.