The book is what the title suggests. Ackerman looks into the work that's been done in testing how smart birds are, or can be, and in what ways they're smart.
Each chapter deals with a different aspect of their intelligence. So one may deal with their ability to navigate, how we've tested it, what we've learned, what we still don't understand, whether their gifts in that area constitute "intelligence". Other chapters deal with tool creation and usage, or their vocalizations, or their social connections.
Ackerman clearly has a lot of enthusiasm for the subject, and she'll add in her own experiences with observing bird behavior among the discussions of research into the topics. Her stories tend to involve birds that most people in the U.S. would be somewhat familiar with (such as the one about a jay trying to drive a crow off a feeder with a pointed stick, only to have it backfire), emphasizing we aren't just talking about certain rare species in far-off lands. There are birds all over the world that exhibit some of these traits, albeit often belonging to particular families of birds. The corvids - crows, ravens, those guys - are pretty exceptional in tool usage and problem solving. Pigeons and the like not so much, but they have outstanding navigational abilities.
The book provides a look into a lot of the discussions that are going on, the differing theories, and ways people come up with to test the birds. If a dead jay is laid out on a yard, and one jay notices and calls others over, what does that signify? If they all stand in a circle around it for some time, then eventually fly off, is that a sign of intelligence? Or, how much does a lack of predation pressure contribute to being able to use tools?
'For birds, it seems, the quality of relationships, not the quantity, calls for additional brainpower. The mental challenge is not remembering the individual characteristics or hundreds of individuals in large flocks or roosts or managing a large number of casual relationships. The really demanding task - at least from a psychological and cognitive point of view - is forming close alliances, especially forging bonds with a mate and providing long-term parental care to young.'