How do birds fly through foliage?

There is a hedge next to my backyard patio. I have often sat on the patio and marveled as the finches, sparrows, and other birds flit in and out of it, despite what seems to me to be an impenetrable thicket of branches and foliage. How is this possible?

Well, my friend Nancy must have been reading my thoughts yesterday as once again I saw this happening. She sent me this link, which uses slow motion to clearly show how a goshawk, a much larger bird than the ones around my house, flies through very narrow openings.

http://www.wimp.com/tinyspaces/

Northern Goshawk - image courtesy sierraforestlegacy.org