In my humble opinion, to write a great non-fic book, you need one of two things: a great story to tell, or the ability to write a great story. Unfortunately, while this book is by no means poor, i dont think it quite ticks either of those boxes.
For starters, Shearwater is simply too long. If you cut out around 70 pages or so, i think it would read a lot better, but therein lies another problem. The book reads more like a loose collection of stories and essays than a proper joined up work. There are some enjoyable parts for sure: the history of Shearwater research is fascinating, and the last 50 pages or so are definitely strong, as you can actually feel the authors author's emotion, something i felt was a but absent for large stretches. Unfortunately, just when part of a chapter or story sounds interesting, it ends, and the book feels disjointed and meandering as a result. The author often writes as though he expects us to know right from the off what he is talking about, and who these people are, and why this story or that memory is important. Finally, this is quite a repetitive book. I will definitely never forget the weight of a Shearwater, how long they live, how many miles they travel, or how long they take between coming to land, because the author repeats all of these facts seemingly at least once a chapter.