Incubation, the act of providing proper physical conditions for the development of certain living organisms. The eggs of birds are incubated from the time the eggs are laid until they hatch. Most birds incubate their eggs naturally, by sitting on them in the nest to keep them warm and moist. Poultry farmers usually incubate eggs in large devices called incubators. The incubating period for eggs of chickens is about 21 days; of turkeys 28 to 30 days; of geese 30 to 35 days.