The purina formula is listed on a white tag that is sewn onto the bag usually on the bottom where the bag is sewn shut.
The head arched over the back is "posturing" it is a sign of nuerologic illness or trauma. Posturing most often occurs in baby quail with an infectious disease known as encephalitis--- this is highly contageous to quail and can be passed en vitro from hen to egg or from direct contact (chick a has it and shares the wealth with chicks b, c, &d... and so on) another sign is ataxia (difficulty walking) as well as lethargy, poor feeding and decreased thirst, heres some info...
http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/205300.htm&word=quail,encephalitis
Unfortunately most causative agents are viral and do not respond to antibiotic therapy. It certainly wont hurt to start them on antibiotics just to cover your bases. I suggest careful observation for repeat signs such as others exhibiting the "posturing" signs of the illness. And strict biological isolation from any/ all other poultry you may have. Bleach everything that you may have even thought of using with this brooder batch, and strict handwashing before and after handling anything associated with them.
I may take some heat for this, so i will simply state that this is my opinion---- THROW THAT DUMOR FEED OUT! I wont even feed that junk to my neighbors chickens and i hate those birds....
Dumor is regular chick starter, NOT GAMEBIRD STARTER, and yes i know it states ducks, turkeys, and gamebirds on the bag--- 20% protien is woefully inadequate for any of the speces listed on their bag except chickens ( guineas maybe? i dunno from nothing about guineas... somebody help me out on this 1? ) My point is it is chicken food--- these arent chickens these are quail and have much different nutritional needs than chickens (more than just the protien % too..) Think of it this way, we have cars on the road that use gasoline, and cars that use diesel fuel--- put 1 type of fuel in the other type of car and see how that works out for ya? Also there could be a remote chance that is nutrition deficit is whats causing your losses (remote) you can try some of the baby vitamin drops in the water font and see if any ill chick's condition improves (must have full spectrum b complex vitamons in it to work if this is the cause...)
check your purina bag for the tag--- it will say "startrena" somewhere on it and list the dietary requirements it covers--- protien will be 30%