This is a good thread.
I grew up on a farm and we kept chickens. Mom and dad used the pelvic bone to determine if a hen was laying or not. It did not always work but I think it would have if they had used some of the other methods mentioned here too. Our chickens were free range.
Some things I learned as a kid about chickens.
1. One of the boldest creatures on this planet is a very angry hen defending her chicks.
2. Free range chickens can be very creative when it comes to finding ways to get into your garden.
3. Once in the garden they can ruin a lot of vegetables in a short period of time by taking a bite or two out of each one.
4. Never underestimate the intelligence of a chicken.
Not too long ago I came across a forum where a lady was talking about using her chickens as a form of organic pest control in her garden. She said it was a brilliant idea but was frustrated too. She said she kept telling her hens not to eat the vegetables "But they just don't listen." She reminded me of the person who once called the state highway department to complain about the placement of a deer crossing sign. She said that the sign had been put in an area where there was a lot of traffic and when the deer saw the sign they would mistakenly think it was safe to cross there.