I dunno as numbers over 4 or 5 or 6 really represent *average* lifetimes (even aside from the whole stewpot issue)... certainly chickens sometimes *do* live to 8 or 10 or 15 or even older, but it seems like the great majority of chickens succumb to something earlier.
I would very strongly suspect that the degree to which chickens are exposed to predators (hawks, dogs, etc etc) has a lot to do with their chances of reaching a ripe old age.
But there are diseases, and "female troubles", and injuries, and social disputes, and so on, too.
Does anyone here who's had their flock for, say, 15-20+ years by any chance happen to have records of what age each chicken that died, died *at*? That would be really interesting to see.
I knew a lady with a 23-year-old buff cochin. It had stopped laying years ago, but it was a good broody, so she kept it, and it raised dozens of chicks for her. It was also a sweet, gentle bird, and the grand children carried it all over the place, rode it around in wagons, the whole thing.
I know that's not statistically significant. . . .
My oldest rooster lived to 6, he was very healthy and very strong, im certain he would have lived a lengthy life! but the skunk grabbed him up ..He was really an awesome rooster!
I had a hen that was about 9 years before she died....she was killed in a barn fire but was in great health. Her buddy was also a retired old ewe and they just got to roam about. She was the queen of the barn!
I strongly question the average of 8-10 years. That seems very high to me. I would think the average is about 3-4 years, in my experience, they get old by that time. I am not saying that they could not live longer, but not on the average.
I think the weather also strongly might influence a shorter life span. I am far enough north, that we have quite short days in the winter, plus cold, snow and rain. This might cause enough stress to shorten their lives, even though they have shelter and food.
I have had several that just died from old age between 3-4 years old. They were just hatchery chicks, not anything fancy. Maybe with a higher quality chicken they would last longer, but I would not get my hopes up too much.
I keep all my birds until they die naturally, unless they have to be put down due to illness. The average age seems to be about 8, although my oldest roo was 11. The breeds especially developed for laying had a much shorter lifespan as I guess they burned themselves out producing so many eggs.