Ask Dr. Tom: Do rocks aid in digestion?

My friend killed a gobbler, and when he cleaned it he discovered the craw (crop) was full of rocks — 6.6 ounces, in fact. I have never seen this and wanted to know if this is normal. Nothing else was in the craw but rocks. The bird was otherwise healthy. Please let us know what you find.

Rick Harrell, Russellville, Arkansas

Wild turkeys pick up and swallow gravel and small stones to aid in their digestion of hard food items. Generally, they pick up the stones a few at a time. When food or gravel are swallowed, they move down the esophagus to the crop, a baglike structure located just above the wishbone. Some digestion takes place there, but the real process of breaking down food items occurs in the stomach and gizzard. These are known to biologists as the proventriculus and ventriculus. 

Birds have no teeth, of course, so they break down hard objects by using a grinding motion in the stomach and gizzard. The gizzard (ventriculus) is a muscular organ that is rough inside. The rough internal surface and the gravel that is swallowed grind food items into small enough pieces that can be digested and provide the necessary nourishment for the bird. Eventually any stones or gravel swallowed will be ground into extremely small particles and will pass out of the body with excrement. This process takes time, and wild turkeys must continually replenish their supply of grinding material.

It appears that the gobbler your friend harvested in Arkansas had spent considerable time picking up rocks! Gobblers generally do not eat heavily in the spring when their minds are on breeding; however, they still need grinding material. I can honestly say I have never seen a wild turkey crop with that many small stones in it. That said, I have seen some very full crops (or craws). It seems this gobbler simply got carried away with pecking at and swallowing stones. He definitely had enough to last a while.

Please congratulate your friend on his success, and thank you for sharing that unique photo of the stones this bird had consumed.

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