Anyone Know More About Storks Being a "Dirty Bird"?

This is a patch I found at an estate sale, but I know little about it...

Embroidered on the green velvet, is a stork delivering a baby. The text reads "The Stork Is A Dirty Bird".

I grabbed it up, for such a stork referencing the old myths of where babies come from fits my perception of my collection. (And I do have quite a few very innocent stork items for such reasons -- plus, storks are entertaining as they go from cute to comical.) But I have no information on what significance the saying has, nor a clue as to who would wear such a patch (or perhaps it is a pocket due to its shape?).

I figured the internet would clue me in on the history, but no luck. If you have more information, post a comment or email me. Thanks!