This photo is a wonderful profile of the behaviors immediately preceding copulation in Caspian Terns. The male is balancing on top of the female's back with a small cyprinid (6-7 cm) long in his bill. The female is not quite in the lordotic curvature (fully swayed back with raised tail) that will allow the male to turn his tern tail under hers in order to make the 'cloacal kiss' necessary to transfer gametes. It almost certain the female is making a highly pitched call reminiscent of a chick begging for food. Often copulation follows soon after (<10 secs) the female takes the fish, but I have seen females take the fish and then dump the male and males that eaten the fish after a cop.