What does ragged as a jaybird mean

It is used in several contexts, one of them is "stark naked", when it is used like "naked as a jaybird", or in this case, when someone needs to take a shower, or change their clothes because she or he is scruffy, dirty or smelly, You may hear "go change your clothes, you are ragged as a jaybird", the color of the bird gives an appearance of dirt that is related to the popular saying.