As a reading teacher and huge fantasy fan, I am always on the lookout for books like this. At a reading level near Harry Potter and Redwall, this book fills a great niche for emerging readers looking for stories that take their them seriously.
There are many rich themes to this book, including community, loyalty, coming of age, war, and diversity, but my personal favorite was its take on religion. The bats hold a certain reverence for the humans in this world, believing that those they "band" have been chosen for a special purpose--a blessing to some, a curse to others. It's a brilliant way to deconstruct religion, as the reader knows first hand that there is nothing supernaturL about humans. Seeing the many interpretations the bats have about the bands provides a potent allegory for the way humans, too, use spirituality in an attempt to explain that which lies beyond their understanding.
There is magic in Silverwing, but it is subtle. A blind bat elder tells a fortune by "listening" to the future, and a few other bats are able to create illusions through their mastery of their "echo sense." The real-life scientific inspiration behind these powers delights the reader with their verisimillitude, and it is beautifully easy to get lost in the sounds and smells of this fantasy adventure.