Diamond Dove and Finches - a question

[peepsnbunnies]

I have a large cage with Zebra Finches and a pair of Diamond Doves in it.. The Diamond Doves have hatched out a pair of babies. The babies have their wing feathers and are coming out of the nest, sitting on the side. I notice today the babies are bald on top of their heads and backs. As I was watching, a couple of the finches flew over and plucked a feather off the babies and ate it! I promptly set up another cage and moved the dove family out. But I thought I read something somewhere that feather eating is caused by a deficiency of something. I can not remember what though. Has anyone heard of this?

Thanks,
Lisa