Bird Gizzards and the Old Grind by Jim Cane

Chicken Gizzard
Chicken Gizzard
Copyright 2013 Jim Cane
Chicken GizzardNaturally polished dinosaur gastrolith found near Duschene Utah
Copyright Rick Dunne, Photographer

You may think of “the old grind” as your workweek, but from a dietary perspective, the old grind links your holiday turkey with dinosaurs. Before making gravy this Thanksgiving, find the densely muscular organ amid your turkey’s giblets. This is the turkey’s gizzard which preceded the living bird’s intestine. In its tough-walled gizzard, a bird mechanically breaks down hard or tough foodstuffs like we mammals use our molars. Reducing chunks to crumbs gives digestive enzymes the large surface areas needed to efficiently digest food.

Being toothless, birds must swallow most nuts, seeds, bugs and mollusks whole. In the gizzard, these items are churned, crushed and ground up, aided by ingested sand, grit or small stones called “gastroliths”. A turkey’s gizzard squeezes with twice the force of our own jaws. At 400 pounds per square inch, this force shatters acorns and even hickory nuts. The gizzard works like the ball mills used in mining, wherein heavy rotating iron drums loaded with steel balls pulverize rock ore. Like a gem tumbler, though, the gizzard eventually smooths and polishes its gastroliths. Having thus lost their utility, these stony gastroliths are regurgitated.

Gastroliths did not originate with birds, but rather with their dinosaur ancestors. Piles of polished stones sometimes occur amid the fossil ribs of big plant-eating dinosaurs, such as a massive Seismosaurus skeleton from New Mexico. These beasts had weak nipping teeth, not molars, so those smoothed stones are likely gastroliths. In east central Utah, polished dinosaur gastroliths can be common in the drab mudstones beneath the colorful Morrison rock stratum.

A century ago, ornithologists routinely analyzed the gut contents of dead birds. They confirmed that most birds have a muscular gizzard, even insectivorous nighthawks and swallows. Powerful gizzards typify pheasants, turkeys and grouse, which all eat hard seeds, nuts or tree buds.

Even waterfowl need gizzards. Mallards, for instance, crush and grind mollusks in their gizzards. They choose to ingest grit the size of buck shot and sinkers.

[Kevin Colver; Songbirds of Yellowstone, Mallard ]

Ducks that eat these shot pellets are poisoned by the lead. Making shot with safer metals is ending this needless poisoning of our waterfowl. California and the US military have been leading the way. Today in Utah, non-toxic shot is required for all waterfowl hunting in the state, so now our ducks and geese can more safely pursue what is truly their ancient grind.

This is Linda Kervin for Bridgerland Audubon Society.

Image: Courtesy and Copyright © 2013 Jim Cane
Courtesy and Copyright © Rick Dunne
Audio: Courtesy and Copyright Kevin Colver,
Text: Jim Cane, Bridgerland Audubon Society

Additional Reading:

Farlow, J.O. and M.K. Brett-Surman (eds.) The complete dinosaur. Bloomington : Indiana University Press, 1997.

Desmond, Adrian J. The hot-blooded dinosaurs : a revolution in palaeontology. New York : Dial Press, 1976.

Ball Mill, Wikipedia,

Gizzard, Wikipedia,

The Audubon Society Encyclopedia of North American Birds, National Audubon Society,

Waterfowl Hunting Regulations in Utah: