Food and Digestion

Birds obtain food with their bills, tongues, and feet. Of the three, the bill is the most important. Its shape is adapted to the bird's diet. It may be used to crack seeds and nuts, cut fruit, strain out plants or animals from water, suck nectar from flowers, grasp insects, fish or other animals, or tear flesh.

Shorebirds and seabirds live on fish, crustaceans, mollusks, and many other marine animals, both living and dead. Birds of the inland swamps and waterways eat frogs, fish, small mammals, seeds, and water plants.

Songbirds live mainly on insects. Many species of small perching birds feed on seeds and fruits. Birds of prey often eat smaller birds as well as reptiles and mammals. Vultures and other scavengers feed on carrion (the flesh of a carcass). Hummingbirds feed upon honey and nectar. Secretary birds eat snakes.

A bird's digestive system is composed of the crop, gizzard, and stomach. The crop is an enlargement of the esophagus. It is a storage chamber where food remains until it is passed to the stomach. Hard foods such as seeds and nuts are softened here with mucus before entering the stomach.

All birds have two types of stomachs: a glandular stomach and a muscular stomach, or gizzard. The glandular stomach contains digestive glands that secrete enzymes to break down proteins and partially dissolve bones that have been swallowed. It is prominent in birds that eat their food whole, such as most birds of prey and fish-eaters.

The gizzard is lined with bands of muscles. It contains small stones and grit swallowed by the bird. These facilitate the grinding and crushing of food. In some birds of prey, such as owls and hawks, the gizzard traps indigestible matter, such as bones and feathers, which is expelled in the form of pellets by regurgitation.

Food passes from the gizzard into the intestine, where it is absorbed. Between the small and large intestine are two sacs, the caeca, that absorb water, digest proteins, and decompose crude fibrous food. Solid wastes are excreted through the lower alimentary canal. The kidneys excrete whitish protein wastes.