This is kind of old news, but Andrew Bird has been writing posts along with some other singer-songwritery type people for a New York Times blog called Measure for Measure which is about the process of songwriting. His posts are as eloquent as you would expect them to be and offer fascinating insight into his mind. A favorite quote from his most recent one:
Live shows are adrenaline-fueled and spontaneous: if you want to capture that then you should put out a live show recording. But the kind of record you want to listen to over and over again in your bedroom or car is something else — a carefully carved piece of sound.
In the second post there is a snippet of the new song which is fabulous even in its unfinished state.