naked as a jaybird

Cliché naked; bare. (*Also: as ~.) Two-year-old Matilda escaped from her nurse, who was bathing her, and ran out naked as a jaybird into the dining room. Uncle John sometimes spends a whole day walking around his house as naked as a jaybird.

Bare, unclothed, as in I came straight out of the shower, naked as a jaybird. This simile replaced the 19th-century naked as a robin and is equally unclear, since neither bird is normally stripped of its feathers. Further, the bird it refers to is more often called simply "jay" rather than "jaybird," yet the latter is always part of the simile. [c. 1940]

Stark naked. Why, of all ornithological species, should a jaybird be singled out for its nudity? One explanation is that “jay” was a 19th-century word for a country bumpkin, and since bumpkins were vulnerable to the wiles of others, a jaybird would be vulnerable indeed.