You will find Herald Petrel in your preferred bookstore. You can use this link to choose:
https://books2read.com/HeraldPetrel
Alternatively, since Amazon is the most used store and it is where you can also get a paperback and hardcover version:
Kindle (ePub, DRM free, with in-book illustrations):
Paperback (454 pages, without illustrations) :
Hardcover (terribly expensive, but got 4 colored illustrations inside!):