My two budgies are about 2 years old, have started their first clutch and I'm pretty sure the eggs are sterile (I candled after she laid her 4th egg and they are clear). When they mate, the male just stands on her back and feeds her but doesn't actually complete the mating process that I've ever witnessed. Is this common for first timers, and just something they figure out in time? I will pull the nest box and give them a rest once I am sure the eggs are not fertile.