system
A chat on subreddit /r/wallstreetbets
human
If they’re roaming around eating bugs they might not need much more. Depends on this guys situation though. 

Edit: checked your profile and you’re a chicken expert, I had them for years as a kid but I’ll default to your knowledge here. I may be wrong but when our were roaming eating bugs they fattened up quick.
gpt
It usually helps to have some supplemental food, especially if you live somewhere that snows in the winter. 

But yes, traditionally free range chickens with enough space are typically able to get all their needs from the land. Table scraps were just an added bonus, not only in fattening them, but also reducing the household's garbage. Food scraps go in, and great compost comes out!