This is a "just wondering" kind of question. I have a brooder cage inside my coop. I bought some baby chicks and was raising them in there. About the time the chicks became a month old. I suddenly had 3 hens go broody. One with a lot of determination and 2 who's broodiness is half hearted (I can make them leave the coop and sometimes they come back and sometimes they free range all day and sometimes they would walk around voicing their anger at me or trying to get back into the coop....but the one will fight and bite to stay in the box. Two of these hens are older hens who no longer lay (a Barred Rock and a Delaware) the third is a year old hen who surprised me that she went broody as she is a Rhode Island Red. All 3 pulled feathers and tried to sit in the nest boxes all day. The old Delaware is the one who refuses to leave the nest unless I pick her up and lock her out of the coop. The Barred Rock has gone broody once before. So I began to wonder if it was the sight or the sound of peeping chicks in the coop that sort of gave them the incentive to go broody ? Or could it be that older hens that no longer lay eggs go broody easier? or is it seeing another hen setting that makes more of them go broody? A few years ago I had 6 Barred Rock hens, had them for 2 years and none of them ever went broody.