John Kenneth Terres was an American naturalist and author. He is best known for his popular works on North American birds. He authored more than fifty works, usually writing as John K. Terres.
It's so massive that it would be on my Currently Reading shelf forever. But I'll go ahead and give it a rating, based on just limited reading and browsing over the last decade or so. It is the only readily available source for a lot of details not provided by any field guide or online site, such as percentage of diet from different food sources and timing of brooding and fledging. One of my favorite bits: alternate folk names for the more familiar species. Also nice is that it's more than just species accounts; it's also an encyclopedia of topics and terms related to ornithology and ecology.
Used again today... what a great book! I use it to fill in the details that are left out in the easier-to-use field guides. Weighs a ton and cost a mint. Worth it all.