Department of Physics, Chemistry and Biology (IFM)

In birds, the parental phase of the breeding cycle includes incubation of eggs and rearing of chicks. During the parental phase, the birds have to cope with sudden unpredictable stressors such as deleterious climatic events and external parasite infections. In addition to this, the birds also have to cope predictable stressful events such as the changes in energetic demands like the need to feed chicks and to fast while incubating.

Broodiness is one of the strongest instinctive behaviours that chickens display. A broody has a desire to sit and incubate her eggs with a view to hatching them and mothering a brood of baby chicks when the surroundings are suitable for it. The changes in transition from egg laying to incubation behaviour in birds is associated with changes in plasma levels of steroid hormones and prolactin. The brood patch is a featherless region which birds develop to facilitate warming of their eggs. Birds develop brood patches on the ventral thoracic and abdominal region of their body. The following changes occur in the skin of the brood patch to aid heat transfer to the eggs: (1)  the development of bare areas of skin around thearound the abdominal and thoracic region by feather loss (de-feathering) since feathers are a poor conductor of heat, (2) the epidermal layer of the skin becomes thickened and the dermal connective tissue becomes swollen or edematous and, (3) the blood vessels in the dermal region increases in density and thickness (vascularization), as incubation is initiated. During the early stages of brooding the chicks, the vascularity and dermal swelling regresses and the re-feathers of the brood patch region occurs. The stage of brood patch development is dependent on the stage of breeding exhibited by individual birds. The brood patch plays an important role in mediating a positive feedback between incubation behaviour and hormonal secretion, and its development advances through increased hormonal secretion. PRL, the hormone associated with maintenance of incubation behaviour in birds, is also essential for brood patch formation in avian orders.