Young birds and hens may be put into a flight. Cocks over a year old should not. They may attack and kill each other. The hens and young may also be harassed and mutilated. In any event, flights must be constantly inspected for birds failing or going light.
Large populations bring unbearable pecking order pressures on individual birds.
These low men on the totem pole will rapidly fail. Placed in individual cages they will often recover. Despite all precautions, occasional unexplainable mortalities will occur in any flight. I must here mention the revolutionary system of Doctor Travnicek, budgerigar and grass parakeet breeder. He uses all wire cages constructed of one-half inch by one inch welded wire and fastened with crimped clamps.