I am not entirely sure if Marc Davis drew these analytical bird studies. They do show a sense for observation and research that reminds me of Marc's anatomical explorations. But the writing on these sheets isn't his.
Nevertheless this kind of work is so necessary in order to animate an animal convincingly. When you are at the point where you know the real structure of a creature, then you can go to town and animate, caricature and exaggerate.
Eric Larson did some nice cartoony bird animation on Sasha from Peter and the Wolf. Ollie Johnston animated Orville in The Rescuers beautifully. He also drew key scenes with Archimedes for The Sword in the Stone. My favorite Disney bird animation is by Milt Kahl on The Jungle Book. The way he brought those four vultures to life is mind boggling.
There are a few non personality birds scenes in MUSHKA. Effects animator Daniel Ernesto took care of those beautifully.