The chicks were the right age for banding - big enough to band and not so big as they think they can fly. And accidents do happen, usually its not really a jump but rather they are close to the corner or an edge and get spooked and they try to get out of the way ... not an intentional jump thinking they can fly but it is intentional movement away from the banders .... the chicks are hardwired not to jump until first flights - if they weren't hardwired this way, it would be a major evolutionary flaw ...
... did I make the shades of grey clear enough ??