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Drucilla Shelton, age 12, of Whittler, N. Carolina, for her question:

Why do birds have gizzards?

Now for today's merit question about gizzards. The bird world has had no teeth for the past 60 million years or so. And our teeth happen to be one of the important items in the complicated digestive system. As we know, living cells of the body cannot use the whole foods we serve on the menu. These must be broken down into useable chemicals and pulverized into a liquid formula. Our digestive systems perform these duties    and so do the digestive systems of birds.     

We start the process in the mouth by chewing and moistening each mouthful with fairly mild digestive juices. A toothless bird cannot do this    so he does the next best thing. He grabs a bite in his sturdy beak, then uses his small pointed tongue and the grooved roof of his mouth to mail the package down his throat. Built in muscles push it down the esophagus, a tube that leads to the base of his neck. There it opens into the crop. a stretchable bag where a mealsized supply of snacks is moistened and stored.     

From there it passes into the juicy stomach where the ventriculus, alias the gizzard, waits to do the work of the missing teeth. This remarkable masher and mixer is a tough little fist of heavy duty muscle with a heavy duty lining of thick skin. The gizzards muscular fist crushes and pulverizes the food with assorted digestive juices from the stomach walls.   

 However, many birds dine on seeds, grain and other hard diet items. The gizzard cannot chomp and chew them without some outside help. So the sensible bird swallows a few pellets of gritty gravel. The gizzard mixes them in its muscular food mill. Their sharp edges help to cut and slice, chomp and chew the toughest snacks into digestible pulp. Yet somehow this is done without scratching the walls of the gizzard.     

When this wad of food is properly pulverized with digestive juices, it passes into the intestine. Then the empty gizzard is ready to cope with the next helping of moistened food from the storage crop.

A few fishes have gizzard type digestive organs. Scientists also suspect that at least some of the ancient dinosaurs had gizzards. This is indicated by piles of grinding stones found inside their fossilized rib cages. Maybe the birds did not invent these handy digestive organs. But they certainly perfected them  and the best gizzards belong to the birds who dine on the hardest seeds.

 

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