Maya nodded. "Yes. I'm a human-avain hybrid, as are my sister, Mina, and Annie. We're designed to be faster, stronger, and lighter than regular people. So we burn calories like racecars burn fuel, which means we don't weigh much."
That's when Maya remembered she was talking to a vet. "Of our weight, very little of it is fat or bone." She went-on, knowing Calvin, Terry, and Kalie would be getting lost soon. "Our bones are very light, and they have pores in them that air goes through, making them even lighter. Our organs are slightly smaller than usual, becuase our wings have to be able to lift all out body-mass, and our lungs have air-sacs attached to them, so when can still have enough oxygen to breathe right when we're way up high. And our hearts are more efficent, and stronger. Their faster."
She snapped her fingers a buch of times to demonstrate.