This strange and funny phrase has been taken to my attention. On UrbanDictionary I found out that it is used when it's obvious the answer to a question is YES. I still think it's quite a strange saying, though UrbanDictionary gives the same meaning for "Do one legged ducks swim in circles?" as well. But I've found other variants which I'm not sure what they exactly mean: Does a polar bear shit in the woods? Does the pope shit in the woods? What do they mean? Are they answers to question which answer is obviously NO?