自分(じぶん)が生(い)きている意味(いみ)がないと考(かんが)えたから。

Yodaka, having heard the hawk's words, simply could not accept the idea of eating insects. Just thinking about taking the lives of other creatures to live was nothing but painful. Even when night came, Yodaka could not fly, and just stayed alone on the tree. As he deeply pondered whether he was needed by no one and if there was no meaning to his life, his tears wouldn't stop. Yodaka began to strongly feel that he couldn't stay like this, that something had to change.