The owl, especially in children's literature, is often illustrated as an impressive, silent, imperious creature; brooding on its perch like an old judge. It helps that it is a nocturnal creature, of course. It's harder to draw an owl at night, in flight.
I was reading Squirrel Nutkin to Thomas and referred to Old Brown, a particularly wise and patient owl, as a bird.
"You are wrong, Daddy!" Thomas declared, finger in the air. "Owls walk!"