BIRD DIGESTION

bird digestive tract

  1. bill
  2. mouth
  3. tongue
  4. pharynx
  5. esophagus
  6. crop
  1. stomach
    1. proventriculus
    2. gizzard
  2. small intestine
  3. caeca
  4. rectum
  5. cloaca
A typical bird's digestive tract is usually considered to consist of the parts listed at the right. You know what the bill, mouth and tongue are. The pharynx (FAIR-ingx) is the part between the mouth and the esophagus, much involved with swallowing. The esophagus is the tube leading down from the pharynx.

THE CROP:

Not present in all birds, the crop serves more or less as a "doggy bag" when the bird eats. Notice the crop in the picture above. Let's say you're a Song Sparrow and you discover a weed just loaded with delicious-looking seeds, but the weed grows in the open. If you flit into the open area to eat the weed's seeds, you're making yourself vulnerable to predators who want to eat you. What to do?

What you do is to flit into the open and gobble up those seeds far faster than any stomach could possibly handle them, then fly to safety. You can do this because of your crop. For, as you cram in those seeds, a few at first go straight to the gut but, when that fills, further seeds begin detouring to the bag-like crop. Once the crop is full of seed, you fly to your favorite perch, and now there's not much to do but let your stomach digest. As those first seeds in the stomach begin working their way through the rest of the body, seeds stored in the crop automatically refill the stomach. If someday you pick up a bird, perhaps one that has flown into a window and you want to save it from the cat, if that bird has recently eaten, you well may be able to feel the crop in the chest area, feeling like a bag filled with grit right below the feathers.

Actually, specialists in the field of bird guts would want to insist that some birds have real crops, other birds have "pseudocrops," and that there are other croplike variations, but we don't want to get too confused so we'll just leave it at that.

THE TWO-CHAMBERED STOMACH:

BEYOND THE STOMACH:

Once food leaves the gizzard, its voyage through the intestines is fairly similar to that taken by food in our own intestines; nutrients are absorbed into the body, and waste is eventually excreted. Intestines are short in birds which eat easily absorbed food, such as fruit, flesh, and insects, but long in species eating seeds, plants, and fish. Swifts, which are insect-eating birds you'll see skating across the suburban summer sky, possess intestines only about three times their body length. In contrast, intestines of vegetarian ostriches are roughly twenty times their body length. Easily absorbed berries pass through a thrush's intestine in less than half an hour, while rougher food may need half a day or more.

The word "caeca" (SEE-kah)is the plural form of caecum (SEE-kum), and the plural form is used here because birds usually have two. Caeca are very variable among the species, often looking like two little worms stuck at the end of the intestines. Their usual function  appears to be to aid in the absorption of water and proteins, and the microbial decomposition of fiber.

The rectum is the last part of the large intestine in humans, and no digestion or absorption of food takes place there. The cloaca (klo-A-ka) is the end of the line where waste from the digestive and urinary tract, and a little other stuff, accumulate before being dumped.