How does Palmer react in Chapter 13 when he is awakened by tapping? Who does he think is at the window? What does he find?

Palmer wakes to the sound of tapping and realizes it is not his mother but instead someone tapping at the window. He leaps out of bed thinking the gang is there but finds instead a pigeon at the window. He does not want the pigeon to stay, believing Beans would first laugh at him and then kill the bird.