Gizzard Stones

Just about everywhere one cares to look, Nature has placed objects to fascinate the mind. Even in the dirt particles beneath our feet there are many intriguing stories about the present and the past; the trick is to be observant and to question what one sees.

Several years ago, archeologists sieving Fairbanks area dirt in search of small prehistoric bones and human artifacts found in their screens many highly-polished small pebbles of quartz and chert. Puzzling over the origin of these usually rounded but sometimes angular shiny stones, the scientists considered several possibilities.

They decided that wind-blown sand or ice crystals could not be the answer because these agents would carve facets on the polished stones. Nor did polishing from natural tumbling of the soil by frost action seem to explain the combination of rounded and angular shapes found, since tumbling causes all stones to become round.

Then Charles Hoskin and his coworkers realized that these objects might be gizzard stones, called "gastroliths", ejected from grouse and ptarmigan of long ago. Comparison of the stones with those taken from the gizzards of modern grouse and ptarmigan led to the conclusion that the polished stones were, indeed, gastroliths. The polishing given to bird gastroliths comes from chemical action and physical grinding as willow and spruce buds, seeds and other hard-to-assimilate foodstuffs are ground up in the birds' gizzards. Sharp, angular stones are picked up in spring and summer; as the year progresses, the stones become more rounded.

One mystery remains. Some of the gizzard stones found in the soil are larger than present-day birds are known to use,a hint that some grouse of ptarmigan of the past were larger than those that live now.