What Are Feather Stress Bars?
Ron Hines DVM PhD
During the period that a feather is forming, the follicle that produces that feather relies on a steady stream of nutrients (the amino acids needed to build a feather β-keratin protein [ref]) obtained from the nutrient proteins in a bird’s blood stream. If that steady flow of food nutrients is interrupted, either by a lack of food or an disinclination to eat, the feather will no longer develop normally because the feather-forming cells that line the feather follicle can no longer produce the keratin proteins needed to form the structure of the feather. When those nutrients again reach their proper level in the bird’s blood stream, feather development returns to normal. So a careful examination of a bird’s feathers gives you and your veterinarian a look back into its past. In this particular dove, I apparently missed a scheduled feeding while the feather I am pointing to was developing. That resulted in the narrow white line – like a scissor cut – present to the right of my finger. You can see that even the integrity and strength of of the feather shaft was compromised at that point. With time, that feather will break at both points. You can read a bit more about the problem and feathers in general here.
Disease and environmental stress are also accompanied by weak, imperfectly-formed feathers. I cannot tell you if it is just a lack of interest in food in those situations that accounts for them or if those feather defects form through a different mechanism. Whatever their cause defective bands only form in developing feathers (“blood feathers”). They do not become apparent until the feather has fully unfurled. When these bars occur in a bird you are hand-feeding, the most common cause is not feeding frequently enough during the day. Feather beak disease of parrots also causes deformed feathers. But they have a different appearance than stress bars.