The act of spitting the jizz from a prior blowjob back into the guys mouth.
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.
"Dude, I heard you broke up with Larissa"
"She gave me the fucking mother bird!"
"Dad, why does your breath smell?"
"Your uncle just gave me the mother bird"
"WHAT THE FUCK?!"