I noticed you said most of them were 5 days old. How old were the other ones? I put some babies in the brooder with some that were around 2 or 3 weeks old and I found several of the smaller ones dead. I think the older ones helped to kill them but I could be wrong.
Shipping is stressful on chickens/quail/fowl to begin with and they can be a little weak when they arrive and then not stay warm under the heat lamp. I've lost several this spring for no reason that I could see but I think they got too cool in the brooder.
