There is plenty of detail in the main text, but the captions for the illustrations add even more. And let me just say, the illustrations are excellent. You can see the feather tufts on the great horned owl, the protective coloration that lets a screech owl blend into the branch it is sitting on, and even the scorpion hanging out of the elf owl's beak. Special physical features such as the talons on an owl's feet that help them grip their prey or the facial disks that direct sound to their ears to make their hearing more acute are all shown and explained.
I also like the way Pringle talks about how owls have been viewed throughout history. Some people, like the Athenians, revered the owl and linked it with their goddess Athena. Other groups like the Mayans considered owls an omen of death. The author even mentions Harry Potter's owl, Hedwig. And in the back matter there are lists of books and websites where you can learn more. There are also a glossary and an index - very helpful for doing research.
If you enjoy this title, you may want to check out the rest of his Strange and Wonderful series, which includes Octopuses, Sharks, and Bats (to name just a few).