Pieplow's books on bird song are fantastic. Each page has a tiiiiny picture of the bird up in the corner, then a big spread of spectrograms and a decent chunk of text to give the spectrograms context: eg, what are the 'typical' parts of it, vs what varies, how likely it is that subsequent vocalizations are the same/different, what to expect in variations by sex and age, and so on.

But my favorite part of the book is the introduction. In addition to just a great intro to reading spectrograms and what's up with bird vocalization physically (they have a syrinx, not a larynx), there's a lengthy section with a kind of 'phonetics' of bird song. It's great.