Living Dinosaurs: The Evolutionary History of Modern Birds is an academic anthology of key writing about bird evolution. There are two main things that distinguish this book: 1) It includes quite a bit on fossils and their bearing on bird evolution, a refreshing change from DNA-based phylogenies which can by and large only address later questions of bird evolution; and 2) It includes a lot more about the early evolutionary context of birds (such as in the context of theropods) than one usually sees, rather than the diversification of birds per se, though it does address the latter as well.
The book offers an excellent summary of our the current state of knowledge of the origin and evolution of birds. Avian palaeontology had developed in fits and starts, with some of the most important work being done at the very same time as the beginnings of modern evolutionary biology (TH Huxley wrote the key monograph on the first recognized bird fossils), with long periods of relative quiet, then sudden re-evaluations of avian evolution recurring with new discoveries. A modern perspective of bird evolution is quiet different from what dominated even a couple of decades ago. Living birds are a single stem of a diverse radiation of forms within the dinosaurs, with our feathered friends of the present being a very limited representative of that ancient diversity. This, of course, is why the book focuses so much more on fossils than DNA; Direct genetic data is simply unavailable to address these questions.
This edited volume (Gareth Dyke and Gary Kaiser editors) is divided into three main parts. Part one deals with deep evolutionary time, addressing Therapod diversity and Mesozoic avian divergences; The second part addresses the early diversification of modern birds and the Avian tree of life; Part 3 looks at key Avian adaptations such as flight, the interesting and the unique bird brain. Then there is fourth part that serves to tie it all together, addressing the state of living birds and the future of Avian diversity.
This is an academic book and the price reflects this. It’s about $130 list, though the link I provide above will get you a copy of this baby at far less ($90 bucks or so). This may require a trip to the library if you find this interesting!
If you are interested in birds and dinosaurs, have a look at “Are Birds Really Dinosaurs?” at 10,000 Birds.