Holden, the protagonist of the novel The Catcher in the Rye, romanticizes nature. It seems that he is most at ease when surrounded by images which are related to nature.
When Holden first comes to New York, one of his first concerns is to find out where the ducks go during the winter. He seems truly saddened at the fact that he cannot find this information out.
Later, when looking for Phoebe, Holden decides to go to the Museum of Natural History. It is at the museum where Holden begins to remember his own "childhood." Holden's reflections on the museum trips he took when he was younger always made him sad. He seemed to find it saddening that every time he visited the museum he had changed, but the museum had not.
The importance of this theme is that it seems that Holden wishes to go back to a place in his life where time stood still for him. His brother, Allie, would still be alive and D.B. would still be home. The Museum represents Holden's desire to not grow up, to remain forever young, to be frozen in a happier time.