Hi, thanks for playing!
Normally, moving enemies can be killed using the compact formation, even with a large flock.
However, the larger your flock gets, the harder it becomes to maintain a V formation while dodging obstacles. This is intentional: the goal is to increase difficulty as you grow and to force players to balance between using a compact formation to avoid losing birds and a V formation to avoid losing energy.
It's really difficult not to lose any birds, but the goal is to keep as many as possible.