Red-necked Grebe feather exchange

I was down at the lake watching my favorite Red-necked Grebe family one June day. The parent on the nest plucked a small feather after it was done preening. It then engaged in what seemed to be a game of pass the feather. They shared it back and forth a couple times until the chick could not keep hold and it flew off onto the parent's head. I have also read that the do this to practice for exchanges of small fish as well and that they actually eat the feathers to protect their digestive system. Whatever it may be it sure was adorable to watch!