Our Amazon, conure, and parakeet pairs always seek our fresh greens, celery, buds, and such on the first days after the hatch. Incubator chicks, too need such green food. Where green juices are not available, use spirulina. Especially for this article, I talked with expert aviculturist Dale Thompson. Stunted skin does not rebound.
Dehydration is the first problem.
In macaws, one sees a body out of proportion with large head and feet. He added that it is the belief of experts that such birds will grow into adults but will have brain damage and in several generations of stunted babies, pelvic problems will begin to show. I recently went to a friend's house where there was a new incubator. At 14 days, they were very undersized. Nutrition, feeding amount, and schedule were all optimized to a professional level and daily weight charts were kept.