。
It's painful to see him in such a sorry state.
Literal
Tail-feathers worn-out his appearance [object-を] seeing [topic-のは] unbearable [copula-ね].
尾羽打ち枯らした is a literary idiom — 尾羽打ち枯らす literally means 'to have one's tail feathers beaten and withered,' describing someone in a miserable, fallen state. 忍びない means 'unbearable, too painful to watch.' ね seeks sympathetic agreement. Very literary vocabulary.