Baby chicken hitbox taller than 1/2 block

Baby chickens cannot fit inside of 1/2 block spaces.
(They cannot escape through a half-block space. If they are situated in the same block as an upside-down half-slab, they will behave as if they are inside of it. If they are situated on top of a right-side-up half-slab with a solid block above, they will suffocate.)