In chapter 2 of The Catcher in the Rye Holden visits his professor, Spencer, at his home.  While Holden is “shooting the bull” with his professor, he tells us that he was thinking about something else.  He was very concerned about the ducks that live in the lake in
Central Park.  He worried about what happened to them when the lake froze over and they had to find somewhere else to go.  Though Holden never says it, it may be that he was, in a way, the ducks.  He had gotten kicked out of Pencey and was not sure what he would do or how his life would turn out.  When he talks about the ducks he says that he wonders if they were gathered into a van and brought to a zoo, or if they simply just flew away.  The equivalent to the ducks being brought to a zoo in his own life, would be his parents sending him to yet another boarding school where he would be walled in.  While the second option of the ducks flying away would be him being on his own and doing what he wants.  Holden is conflicted, he doesn’t want to disappoint his parents, but at the same time he wants to be happy.