and bath your birds regulary so natural oils on feathers are kept fresh and use nesting bowls with good ventilation and nest box floor grills under bowls keeps the air circulating , deaths on nest can occur for various reasons too much nesting material and not enough and sometimes inexperienced breeders can trample or sit ybs to tightly and crush the ybs other reasons are birds may be to geneticaly similar and inbred so breed unviable young birds or birds may be disturbed come off nest or if using lights havent had time to settle down when light turned off ;-) hope i have given a bit of food for thought ;-)