23% dropped out of their own volition and 21% were removed for a mixture of medical, safety and performance reasons.

23%的参与者自愿退出， 21%的参与者因为健康、安全和表现等原因被退出。

They move of their own " volition" – that is, on their own, without being moved by a human being.

他们按照自己的“意志” 移动——也就是说， 他们自己移动，没有被人移动。

They seem not to fly of their own volition, but, scatterbrained, to be tossed from tree to tree like wind-blown leaves.

它们似乎不是自愿飞翔，而是漫不经心地像被风吹落的树叶一样从一棵树扔到另一棵树。