Hi, I don't have a problem, I am just a little confused about broodiness in hens. I know some hens will have a tendency towards broodiness, but will a broody hen be broody from the start, and remain so as long as she is laying, or could a hen that has not been previously broody randomly become so?
A hen is typically broody OR laying, not both.
For a hen that will go broody, she does certain things in a particular order:
first, assemble a clutch of eggs. (Lay an egg every day or so, act like any other normal hen.)
second, sit on those eggs. (Stay on the nest all day and all night, but not lay any eggs. She will tend to get off about once a day to eat, drink, poop a lot, and maybe take a quick dust bath.)
third, keep sitting while the chicks hatch. (They should all hatch within a day or so of each other, because all the eggs started to develop at the same time when the hen started to sit on them.)
fourth, raise the chicks. (Keep them warm, lead them to food and water, protect them from other chickens.)
fifth, decide the chicks are mature enough, so she can go back to acting normal and laying eggs. (I've read of some hens "weaning" the chicks as early as 3 weeks, while others may continue looking after the same chicks for months. The time when the hen starts laying again is also highly variable.)
Not-broody hens just get stuck at the first step, assembling a clutch of eggs, and don't go on to the rest of it.
If you're looking for what breeds go broody--I've seen it with Red Shouldered White Yokohamas from McMurray Hatchery, Cornish Bantams from Ideal Poultry, and Red Jungle Fowl from Ideal Poultry. For each of those breeds, I had 2 or more hens go broody, and in each case it was half or more of the hens I had. I've had other hens go broody too, but not enough to make any guess at rates or percentages.
In general, I think rare breeds are more likely to go broody than common ones, because they have not been as heavily selected for "production" traits (like non-broodiness.)