When the beasts seemed like winning, the bat went to them and said, "I would like to fight with you." They believed him.
Yet, the bat began to worry, as the birds started to move ahead. So, the bat went to them and begged, "I am on your side because I am winged, too."
They pleasantly accepted the bat. "Sure. Since you have wings, you are on our side." The fight between the birds and the beasts continued and the bat went back and forth to the winning side.
Then one day, peace was made in the woods. The birds and the beasts learned that the bat went hither and thither between them. All the animals determined to expel him. Turned away from both sides, the bat started to live in a dark cave.
Once upon a time 很久很久以前，曾经，从前
against [ɡnst] 违反；反对；对...不利
pleasantly [plzntl] 愉快地；和蔼地，亲切地
accepted [ksptd] 公认的