I enjoyed this a lot more than I'd hoped to, given the somewhat uninspiring blurb, which basically reads as: 'musician/philosopher starts thinking, and comes up with a revolutionary new explanation for why birds sing that scientists have missed: because they want to!'.
So many things are wrong with that, and they're pretty obvious, so no need for me to diagram it out.
Pleasantly, the book is better than that, and Rothenberg does turn out to know the difference between 'things that I would like to be true because they feel right' and 'things we can actually test (or prove, in the old sense of the word)'. He also sees the benefit of both approaches, and mostly manages to walk the line between both worlds without too much dipping into 'god, scientists are dull and uninspired and fail to notice creativity - also, did you know they kill animals, which is bad, and they don't think about that enough' too much. That tone does turn up a bit, accompanied by small bouts of swearing from me (yes, painting scientists as unfeeling and unethical is one of my buttons, not to mention being so bloody cliched), but on the whole he balances it out, in the end sticking to the point that all the approaches to studying birdsong - music, science, poetry - have their own goals, and their own advantages. Both approaches also might have elements or expertise that can offer some enlightenment or inspiration to the pursuit of the other.
I appreciate the way that Rothenberg has woven in a bunch of different strands of people thinking about bird song, both in science and art, into his personal narrative of just wanting to find ways to make music with birds. He's not shy about pointing out that this is his personal story and opinions, leavened by some other stories, music, or poems he's been hearing or thinking about, but he's interesting, and he's assembled a lot of interesting and wide-ranging stories into this book, which makes it overall (with my mini-breaks for occasional swearing) a pleasure to read.