Sounds in the Night

  It's 1:25 a.m.  and  I'm sitting at the computer, the kitchen windows open behind me.  The other 2 inhabitants of the household have been asleep for hours.  Suddenly a noise, a strange scrambling, scratchy crashing sound, with about 5 stages of intensity, seems to be close to the house.  But there's nothing there, except the trees in the back.  No train has gone by.  I look out the window, I call out.  No response.  I conclude (sort of) that a tree must have fallen in the wooded area out back, and the sequence of different levels of sound must mean it has hit other trees and brush on its way down.   That has to be it, I tell myself.  But what causes a tree to fall when it's not windy?  Something or somebody climbing it?  It made a loud noise.  A raccoon maybe, certainly not a bear......