After giving oral sex and the male has ejaculated into ones mouth, the person has to pretend to sallow but quickly leans in for a kiss and spits the semen into the male's mouth, therefore coining the name Mother Bird.
"She gave me the fucking mother bird!"
"Dad, why does your breath smell?"
"Your uncle just gave me the mother bird"
"WHAT THE FUCK?!"
John: Beware Drew, for she is the motherbird. She knows what she is and is more dangerous than the bird with the fanciest plume.