Stone Swallowing   no comments

Posted at 1:52 pm in Teeth

Those creatures which have no teeth of their own have to resort to dentures. Food eaten by birds is crushed by little stones in their stomachs: the grains are taken into a thick-walled muscular stomach of considerable strength and crushed between the little stones as though between millstones.

Small stones are often to be found in the stomachs of birds. You may find them if you are preparing a chicken for the oven. But this phenomenon is still a puzzle in many respects. What makes birds swallow stones? They do not do it because they are hungry. How do birds know when the stones in their stomachs have worn out and need replacing? What makes them pick up only sufficiently hard stones? As yet, we cannot answer these questions.

Not only birds are fond of swallowing stones. Stones weighing from 350 to 500 grams are often found in the stomachs of whales, walruses and seals. From time to time they belch out these stones and this is why there is often a lot of stones from the sea bottom deposited in places where these pinnipeds spend a good deal of their time when on land. One might think that they decided to establish a geological museum on the sea-shore.

Scientists do not as yet know why sea mammals load their digestive tract with such unusual objects. The reason may be that stones help, as they do in birds' stomachs, to crush such hard parts of their food as mollusk shells and the chitinous shells of arthropods. Another reason may be that stones are used in the struggle with intestinal parasites, which are a particular nuisance to pinnipeds.

Animals are especially apt to swallow stones when they have gone for a long time without food. Hence, the suggestion has been made that swallowing stones prevents the stomach from atrophy (the shrinkage of an organ or tissue with resultant cessation of functioning). Thus, swallow­ing stones keeps the stomach busy when it otherwise has nothing to do.

However, it is quite probable that some sea mammals indulge in stone eating for reasons other than that of digestion. Some scientists believe that stones become indis­pensable when the mammals feed particularly well and get fat. As a result, their mean specific gravity drops and they rind it more and more difficult to submerge in water. Sea­faring animals may also swallow stones as to take aboard some ballast and increase their weight. Calculations prove that the amount of ballast is quite large: some seals had as much as 11 kilograms of stones in their stomachs.

January 3rd, 2010

Tagged with , , , , ,

Leave a Reply