My pekin females do the exact same thing. They usually get excited when their pool is clean or it rains or when I put clean water in the water bowl. They both take turns trying to mate the other but not usually at the same time. Mine just turned 4 years old and there are no other males or fowl around for them to copy. They just started doing it one day but I've had the same issue with my box turtles and my rabbits. Maybe it's just me 
