We bought four POL hens about 9 weeks ago and now three of the four are broody. One of those has vanished so may have been taken from her wild nest. The other two are sitting on nothing in nest boxes but won't give up (we don't force them as they will give up eventually). Other hens we bought last autumn have not gone broody and in fact we haven't had any broodies for the past two or three years.
The breeds/type of the three are: a speckledy, a blacktail and a ginger with white tail ranger type. The one young one which hasn't gone broody is a Light Sussex.
My question is: what governs when hens go broody? Is it age, breed, weather, time of year, temperature, daylight or something else?