Book excerpt: For the last 20 years, Alan Powers, who lives near Cape Cod, has experimented with birdcalls--mimicking and answering the calls he hears around his country home, in cities, and abroad in France and Italy. In BirdTalk, he celebrates this connection with entertaining allusions to history, literature, travel, linguistics, and other fields. The result is a charming and erudite stroll through an area of interest sometimes lost in the urban din. Powers reveals "birdtalk" by mapping the history of ornithological studies, quoting such bird fanciers as Shakespeare and Emily Dickinson and discussing specific techniques. In one of the most amusing chapters, he describes his attempts to teach the birds new symphonic riffs on their own calls. This illustrated literary inquiry into birdcalls is a nature book with a gift-book look.