Ruth, Thanks so much for posting this lovely thread. I too have wondered how the chickens used to do it ~ lol. It makes complete sense that they would be hatching out in the spring, with temperature ups & downs, and that that would in turn help them to grow heartier & healthier.
I wish we had some reasonable temps here in Idaho, I would love to turn my little ones (5 day old chicks) out into the sunshine for a few hours ~ sadly, it snowed this morning! We're still getting lows in the mid-20's & highs in the upper 40's & 50's ~ although, this weekend, it is supposed to get up to 64!! Folks will be out sunbathing, you can bet on it! The kids have slept in the treehouse already 4 or 5 times this spring, but then, it's insulated & they are old enough to know how to snuggle into a sleepingbag. :-D
Also, just wanted to say that I love your yard, it's beautiful & green ~ ours still has that sad brown winter look to it. We are just now getting the bulbs poking up through the mulch.
~Red