I'm not sure what the size difference between the sexes are...Yoki is definitely huge, too, and though Taiki is catching up fast, she still has a way to go before matching him. I would say without a doubt that Alto is a boy, though, Lesley-and he will start croaking at the oddest times. For a while, Yoki would go between 2-4 AM...every night. Now, whenever Taiki is moving (day or night) he gets excited and starts. In one day alone, I heard him 6 different times!