The chicken’s life cycle (Gallus gallus domesticus) is a progression of distinct biological stages that transform a single cell into a mature, reproducing bird. As one of the most common domesticated animals globally, its developmental process is predictable and sequential. Understanding this cycle involves examining the physical and environmental requirements that guide the bird from inside the shell to its adult form. This journey is marked by rapid growth, specialized care needs, and the eventual onset of reproductive maturity, which restarts the cycle.
The Beginning: From Egg to Hatch
The chicken’s life cycle begins with the fertile egg, where embryonic development is triggered by warm, consistent temperatures. The incubation period is 21 days, during which the embryo relies on the yolk for nourishment. This process requires a sustained temperature of approximately 99.5 to 100.5 degrees Fahrenheit and 50 to 55 percent humidity to prevent moisture loss. The egg must also be turned regularly to prevent the developing embryo from sticking to the shell membranes.
By day 19, the chick is fully formed and prepares for hatching by absorbing the remaining yolk sac and orienting itself toward the air cell. The final stage is “pipping,” where the chick uses a temporary egg tooth to crack the shell. This initial hole allows the chick to take its first breath of external air before “zipping.” Zipping involves the chick cutting a circular line around the shell until it can push the cap off and emerge, a process that can take several hours.
Early Development: The Brooder Stage
Upon hatching, the chick enters the brooder stage, covering the first four to six weeks of life. The chick is covered in soft down and cannot regulate its own body temperature, requiring a supplemental heat source. The initial temperature should be maintained around 90 to 95 degrees Fahrenheit, gradually reduced by about five degrees each week to encourage natural thermoregulation.
During this time of rapid growth, the chick requires a high-protein starter feed to support its development. The down is quickly replaced by juvenile feathers, a transformation largely complete by six weeks. This physical change allows the young bird to handle cooler temperatures. As the chicks grow, they begin to establish their social hierarchy and interact with flock mates.
Maturation: The Pullet and Cockerel Phase
The adolescent phase begins around six weeks of age and lasts until the bird reaches sexual maturity, typically between 16 and 24 weeks. A female during this period is a pullet, while a male is a cockerel. This stage is characterized by a significant growth spurt as their adult body structure takes shape.
Physical differences between the sexes become pronounced, with cockerels developing larger, brighter combs and wattles sooner than pullets. Cockerels also develop distinct adult feathers, including pointed saddle feathers and long, curved sickle feathers, which are absent in females. The male’s vocalizations change as the cockerel begins practicing the characteristic crow, signaling approaching adulthood.
Pullets continue to develop internally, with reproductive readiness marked by a reddening and swelling of the comb and wattles. Their diet transitions from a high-protein grower feed to a layer feed as they approach first egg production. This maturation develops the structural integrity and nutrient reserves necessary for a productive adult life.
Adulthood and Continuation of the Cycle
A pullet officially becomes a hen once she lays her first egg, typically between 18 and 22 weeks of age, depending on the breed and daylight hours. A hen requires approximately 24 to 26 hours to form and lay a single egg. Peak egg production occurs in the first year, with high-producing breeds laying up to 250 eggs annually, a number that gradually declines each subsequent year.
The rooster, the adult male, fertilizes the eggs, which is necessary only to produce chicks. Hens will lay eggs regardless of a rooster’s presence, as ovum production is not dependent on fertilization. Chickens have an average lifespan ranging between five and ten years, though egg production slows significantly after the first few years.
When a hen lays a fertilized egg and begins incubation, the cycle restarts, perpetuating the species. As hens age, they often undergo an annual molt, shedding and regrowing feathers, which typically coincides with a temporary pause in egg production.