Adaptations of Chickens

Our domestic chicken (Gallus domesticus) originated from the Red jungle fowl, a tropical bird found in Southeast Asia. Archaeological evidence dates their domestication around 3,200 B.C. on the Indian subcontinent. In the 5,000 years since, chickens continue to share similar characteristics with these wild ancestors -- as well as all birds -- that distinguishes them from other animals. They have also developed specific physical features that allow better adaptation to their environment.

  1. Feet

    • Beyond their role as a delicacy in Asian culture, chicken feet ̵1; like the feet of other birds ̵1; reveal much about their ecology and behavior. Chickens have developed particularly strong feet and toes, an adaptation that allows them to scratch the ground, turn over leaves and rake up dirt to forage for insects and seeds. These strong feet, coupled with flexor tendons in their legs, also allow chickens to perch on roosts, a behavior that protects the birds from predators, particularly at night.

    Digestive System

    • Birds have a highly efficient and lightweight digestive system that meets the needs of their high metabolism. A beak replaces the lips and teeth of mammals. Made up of dermis and epidermis, keratin and calcium, the beak is adapted to the food habits of bird species. A wide, medium-length beak in chickens reflects their omnivorous diet. As with other omnivores, the chicken̵7;s crop is longer than meat-eating birds and the stomach ̵1; the proventriculus and gizzard, the avian equivalent of teeth ̵1; isn't particularly muscular. Similarly, the small intestine is longer and more highly coiled than that of meat-eating birds. In chickens, the dual ceca ̵1; outcroppings of the large intestine ̵1; are well developed, an adaptation that allows for food digestion.

    Air Sacs and Pneumatic Bones

    • Commercial chickens grow quickly and have a very fast metabolic rate. As such, they require large amounts of oxygen. Birds' lungs are rigid, connected to nine membranous air sacs. With no diaphragm, birds rely on muscles between their ribs and sternum to expand and contract the chest cavities, drawing air into and out of the air sacs. A constant flow of fresh, oxygenated air across the lungs results in superior metabolic and respiratory efficiency. Chickens have hollow or pneumatic bones, an adaptation supporting flight by keeping body weight light. Air sacs extend into some of these bones, including the skull, humerus, clavicle and keel. Should a pneumatic bone break, chickens have a difficult time breathing.

    Medullary Bones

    • Medullary bone is adapted to provide a source of calcium for egg-laying hens. A chicken hen supplies 47 percent of her body̵7;s calcium to form one egg shell. In a commercial, egg-laying operation, hens cannot produce enough dietary calcium and must depend on calcium from medullary bone. Roughly 10 to 14 days before an egg is laid, under the influence of estrogen, medullary bone is formed in the marrow cavities of certain bones ̵1; including the tibia, femur and scapula. The breakdown of this bone supplies additional calcium to support proper egg shell development. Absent this additional calcium, egg shells would be weak and thin.