Tree swallows mate about a week before the female lays her eggs. Among other things, courtship consists of the male doing a “flutter-flight” in front of the female as she sits on top of her nesting box or near the nest hole. Mating involves the male making rapid “tick” calls as he flies towards the female, who is perched with her back and tail held horizontal. The male lands on the female’s back, and, using his wings for balance, grabs her head feathers in his bill. He then pivots his tail under the female’s and transfers his sperm as the two birds’ cloacas, or vents, touch (referred to as a “cloacal kiss”). Blink and you’ll miss this brief connection. However, it is not a one-time thing — after the male flies off, he quickly returns to copulate again, and repeats this sequence several times.