Donna Howe, age 13, of Poterborougb, Ont., for her question:
How does a bird digest his food?
Two weeks ago, Andy wrote about the human digestive system. You know, then, that all the different foods we eat Trust be converted into simple chemicals: The body can use them only when they are broken down into amino acids, fatty acids and glucose sugar. They can be sent around to the body cells only in liquid form. In the animal w6rld, food must also be broken down into these simple chemicals in liquid form. This is true for birds, bears and even for the humble earth worm.
The meat eating mammals digest their foods more or less as we do. Some vegetarians, such as the cow, have a more complicated stomach and chew the cud. A bird, however, is usually a small, highly active animal. He could not take the time to chew the cud or even to digest a heavy meal. His digestive system must provide him with a constant supply of quick energy. Notice he is always on the go and always ready for a snack.
For the toothy mammals, digestion begins in the mouth. There the food is chomped and mixed with liquid saliva But birds do not have this digestive juice in the mouth and in the bird world, teeth went out of fashion some 60 million years ago.
All birds swallow their food whole. When a woodpecker finds a grub in a tree trunk, down it goes in one gulp. A duck may take several gulps to swallow a frog, but he swallows it whole. A whippoorwill may wait until he has a mouthful of small insects before he gulps them down. An owl may tear his prey to pieces before he swallows it, gulp by gulp.
In any case, the food goes down the bird's throat in a lump. The gullet which leads from the mouth to the stomach may have a small storage chamber called a crop. Earth worms and certain insects also have such a crop for storing food while the stomach is full.
The birds main digestive organ is the gizzard. It is a thick walled bag with a very tough lining. The walls are strong muscles which pound and pummel the food into mash and mix it with liquid digestive juices. Strong a s it i s, the gizzard i s not strong enough t o chomp up all the food eaten by the bird, especially when he dines on hard seeds.
Most birds swallow a few pebbles to help the gizzard grind up tough food. Perhaps you have heard that the ostrich will even swallow nails. This trick is not as silly as it may seem, nor will the nails or the pebbles be digested. The gizzard acts like a muscular fist and with a few sharp stones mixed with the food it can do a better grinding job.