When the man has previously had sex with a woman, specifically in her vagina (see back alley bird bath for anal), and then that same woman (or a different woman) cleans the man's genitals with their mouth; either right after sex or before next round of sex.
A act of desperation in which one needs to shit but can't get to a bathroom. One climbs into tree and takes a dump directly down into a birdbath in order to avoid public detection.
Any Gentleman standing on his tip-toes washing his tallywacker off in the sink after anal sex. Usually performed because the female half will not allow re-entry into her vagina without a thorough scrub.
A Facial bird bath is when a person performs cunnilingus on said woman and she has a female ejaculation (squirt) on said person's face. Hence, like a bird in a bird bath flopping away in the mixture of vaginal fluid and urine.