Bernd Heinrich is a naturalist and professor who has written plenty of uniquely insightful and highly accessible books on the intelligence of birds, among other species.
One of his authoritative books is the "Mind of the raven", which analyzes the question of consciousness in ravens. From the description on Amazon:
"Mind of the Raven follows an exotic journey;from New England to Germany, and from Montana to Baffin Island in the high Arctic;offering dazzling accounts of how science works in the field, filtered through the eyes of a passionate observer of nature. Each new discovery and insight into raven behavior is thrilling to read, at once lyrical and scientific."
Another of his books that particularly sheds light on the unimaginably mature navigation skills and the ultraendurance of our avian brethren: https://www.barnesandnoble.com/w/the-homing-instinct-bernd-h...