Broodiness is a physiological state or maternal behavior exhibited by hens who want to be mothers. Their physiology and behavior will change towards fulfilling this goal. A broody hen will continuously sit on a clutch of eggs in order to incubate them to hatch. During this time, she may:
- Sit in the nest box all day and all night, even if there are no eggs to sit on.
- If she sees an egg, she will take it and put it underneath her.
- Stop laying eggs.
- Eat and drink less.
- Pluck feathers from her chest and abdomen (referred to as brood patches), which is done to help improve heat transfer from her body to the eggs.
- Produce abnormally large droppings.
- When disturbed, she’ll often get defensive and/or make characteristic clucking sounds.
Prolactin (PRL), one of the pituitary hormones, plays an important role in the onset of broodiness. When levels of this hormone increase, it inhibits the production of gonadotropin, which is what stimulates ovarian follicles (what eggs are made from). When an actively laying hen is injected with prolactin, it causes her to stop laying eggs and go broody within a couple of days.
Certain environmental conditions stimulate the onset of broodiness in hens. Warm weather, letting eggs accumulate in the nest box, reduced exposure to light, and seeing baby chicks can induce broodiness.
Certain chicken breeds have a genetic predisposition for frequent broodiness. Silkies, Cochins, Orpington, Plymouth Rock, Icelandic, Iowa Blue, Nankin, Delaware, gamefowl hens, Dutch bantam, New Hampshire, Indian game, Pekin, Belgain Bearded d’Uccle, Booted bantam, and Sussex are well known for their broody behavior, and reputation for being excellent mothers to newly hatched chicks.
Breeds that were selectively bred for excessive egg production, such as the white Leghorn, rarely show broody behavior. This is because broodiness is undesirable for the egg industry, because they artificially incubate eggs through hatcheries.
How to tell if a hen is broody?
Put an egg in front of her, a broody hen usually can't resist moving the egg underneath her. Often, if the hen is picked up and placed somewhere else, she will fluff out her feathers and just proceed to nest in that very location for a few moments, before eventually making her way back to her nest.