It may not be "flightiness," exactly, that takes them over the fence... it may be something as simple as curiosity. When I think of flightiness, I think of my 5 Brown Leghorns, who are a whole different animal from my Easter Eggers. Right from day-olds they were different. The EEs were quietly calm and curious while the BL would go into panic mode over nothing. Still do, 5 months later. You'd think they've never seen a human before! Every single day! But before we clipped their wings, it was the EE that would fly to the top of the 5' fence to see what's on the other side. Just curious, I guess. But not "flighty," at least not in my opinion.