Incubation is a process by which birds hatch their eggs, and to the development of the embryo within the egg.
Incubation period is very critical and maintaining constant temperature required for its development over a specific period is a vital factor of incubation. In most species, body heat from the brooding parent provides the constant temperature. Several groupsinstead use heat generated from rotting vegetable material, effectively creating a giant compost heap while some make partial use of heat from the sun.
The act of sitting on eggs to incubate them is called brooding.The action or behavioral tendency to sit on a clutch of eggs is also called broody, and most egg-laying breeds of poultry have had this behavior selectively bred out of them to increase production.
The incubation period, the time from the start of uninterrupted incubation to the emergence of the young varies from 11 days (some small passerines and the Black-billed and Yellow-billed Cuckoos) to 85 days (the Wandering Albatross and the Brown Kiwi).
In these latter, the incubation is interrupted; the longest uninterrupted period is 64 to 67 days in the Emperor Penguin. In general smaller birds tend to hatch faster but there are exceptions, and cavity nesting birds tend to have longer incubation periods.
Details of egg and incubation period of some birds are given below