Broodiness

Broodiness is the action or behavioral tendency to sit on a clutch of eggs to incubate them, often requiring the non-expression of many other behaviors including feeding and drinking. Being broody has been defined as "Being in a state of readiness to brood eggs that is characterized by cessation of laying and by marked changes in behavior and physiology". Broody birds often pluck feathers from their chest and abdomen, using them to cover the eggs. As a consequence of this, they develop one or several patches of bare skin on the ventral surface. These reddish, well-vascularized areas of skin are usually called brood patches, and improve heat transfer to the eggs. Broodiness is usually associated with female birds, although males of some bird species become broody and some non-avian animals also show broodiness.

In wild birds, egg incubation is a normal and essential phase in the process of reproduction, and in many families of birds, e.g. pigeons, the eggs are incubated by both male and female parents.

In all the species of phalaropes the males become broody rather than the female. The females leave the nest after finishing laying to let the males incubate the eggs and take care of the young. Male emus (Dromaius novaehollandiae) become broody after their mates start laying, and begin to incubate the eggs before the laying period is complete.

A small number of atypical birds such as Passeriformes of the genus Molothrus do not become broody but lay their eggs in the nests of other species for incubation, known as brood parasitism. The Australian Brushturkey (Alectura lathami) also does not become broody, rather, it covers the eggs with a large mound of vegetable matter which decomposes keeping the eggs warm until hatching. The Crab-plover, (Dromas ardeola), which live on the coasts and islands of the Indian Ocean, let their eggs incubate primarily by the heat of the sun and will leave their nests unattended, occasionally for days at a time.

Broody hens can be recognized by their behaviour. They sit firmly over the eggs, and when people approach or try to remove the eggs, threaten the person by erecting their feathers, emitting a characteristic sound like clo-clo-clo and will peck aggressively. When broody, hens often temporarily cease eating or reduce their feed consumption.

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Wikipedia