Read the excerpt from "Return Flight." The crate was used to move him back and forth between the myriad enclosures that made up his strange life on the ground. These creatures seemed to like their enclosures. They spent most of their time inside one kind or another. He didn't understand it. If he hadn't found himself at the mercy of these cage lovers, he would be soaring in the wide open space of the sky, forever free of any kind of container.

According to the excerpt, the crate is most likely a symbol of

civilization.
wilderness.
injury.
love.