Two sibling hybrid jungle fowl chicks. One has a normal skull and other has a vaulted skull also known as a cerebral hernia due to a silkie hen in its ancestry.
Since these chicks are very close to wild type its pretty easy to see how a vaulted skull can drastically chnage the anatomy of the birds head. Still though, this is not as extreme as it can get and i doubt this vaulted chick will have any problems as it grows.
Silkies,Polish, Houdans, Sultans, and Crevecoeurs are some of the breeds who have been purposefully selected for vaulted skulls as it increases the size of the crest on their head. Silkies orginally did not have crests (or beards!) But they were crossed with bearded polish to get the crested, bearded bird we see more commonly today.
Vaulted skulls can be problematic for the bird due to the skull malformation leaving holes and weak spots in the skull where the brain is only protected by skin and feathers. As the bird gets older the bone should grow to protect those areas but that is not always the case for severe deformities.
Breeds like the polish who have been vaulted for hundreds of years tend to have less problems due to sturdier structure but bad breeding can quickly undo that.
Vaulted skulls are associated with lower hatch rates, vision issues due to optic nerve damage, higher chick mortality, deafness, cognitive and motor impairment, and delayed reaction time. These birds are incredibly sensitive to rough handling, pecking order disputes and are an easy target for predators. Head injuries can be disastrous for birds with severe vaults and can lead to severe brain damage.
Birds with severe vaults looks alot different then the hybrid above. A severe vault would be like the chicks below have which are pretty unnerving.
Not every vault will cause problems in the birds and not every crested bird is vaulted as there is different crest types besides the one caused by a vault. (Ill talk about those one day when im more read up if anything is spelled wrong here its because its 6am and i need to infodump)
I have been talking about vaulted skulls more recently and i thought id share some pics i have seen recently to show how variable it can look. Also i do not condone hybridization of wild jungle fowl at all!
