I have a flock of various breeds of chickens, which free range 100% of the time (unsupervised most of the time) on a large property. I have two white leghorns, 6 cross breeds and 4 "green legged partridge fowl", which are a heritage breed and are pretty wild and pretty immune to illness. I started out with 9 green legs and a greenleg rooster, then got the white leghorns. one of the hens has gone broody a few times and so I put a few eggs under her from the neighbour (2 of them hatched) and bought dayold mixed breed chicks when those ones hatched, to end up with 9 chicks. the second time she went broody (she is a bantam green leg) she had been stashing her own eggs in the haystack, and had 9 of them under her. I thought she had disappeared but I found her in there when taking out some hay. All 9 of those chicks hatched (a much better success rate than with an incubator), and those 9 chicks are now 2 weeks old. Anyhow, from my original 9 green leg hens, a few disappeared, presumably taken by hawks during the day, and 4 started to act sickly and then in a day or two just dropped dead with no visible symptoms of illness except a droopy head, disorientation, lethargy, etc (each time the behavior was different, so I don't think it was the same illness each time). This didn't happen to all 4 at the same time, it was one at a time at seemingly random intervals across the course of their teenage months. From the 6 cross breed hens that I bought and put under the broody hen as day olds, 2 have dropped dead in the last 2 months. The two that hatched are still ok and are now 4 months old (one of them is a rooster, unfortunately). I had also three broilers, two of which are ok and 14 weeks old now (time to chop them), but one of them dropped dead a week ago for no reason, and was not acting sick the day before. so, it means that over the course of one season (May to October), out of a total of around 22 chickens (not including the 9 that are now 2 weeks old), 6 of them died for unknown reasons and without symptoms other than behavior changes. I consulted with my neighbours, who mostly have confined or partly free range chickens, and they state that this mortality rate is normal and that they always lose a few chickens here and there. When they notice a chicken starting to act sickly, they cull it immediately, in fact. In researching large poultry farms, I find that there is such a thing as a "calculated mortality rate", basically chickens dying for seemingly no reason, and to combat this (and thus maximize their profits) they use antibiotics, steroids, high protein food additives and a variety of synthetic viatmins and other additives, hoping to reduce this mortality rate to nearly zero. My question is, is a mortality rate of 6 chickens (usually dying before reaching adulthood) out of 22 in the course of a year, in a natural free range situation, normal and acceptable? Please advise.