Why are these intelligent crows "eating rocks"? First time I ever got this on film! Actually lots of animals eat rocks. Or at least they swallow rocks; they don't eat them in the sense of digesting them. This is true of many reptiles and birds and a few mammals such as seals and whales. Rocks that have been in the digestive system of an animal are called gastroliths, which literally means "stomach stones."
Gastroliths are most commonly found in birds, like Crows, that have stomachs divided into three parts: a crop, a gizzard and a stomach. The crop stores food, the gizzard grinds it up and the stomach digests it. The Crows swallow sharp pebbles and grit and hold these rocks in their tough muscular gizzards. The gizzard contracts and grinds the gastroliths against each other and against the food that the bird has swallowed (remember that birds have to swallow each bite whole). The rocks grind down the food — essentially, the bird is using the gastroliths to chew the food in its gizzard — and the rocks grind each other down, too. Eventually the sharp, jagged chunks of rock become smooth, rounded pebbles, and they are not much good for grinding anymore. So the bird will vomit them out and find new, sharp rocks to swallow.
Documentation of this Crow behavior in the wild is actually quite rare. In this case the ingenuous crows have found an area recently dug up by rooting wild hogs and know this is a good picking grounds for rock and pebbles of just the right size and shape. Note the care with which they search and select the stones, picking relatively flat ones with quite sharp edges of just the right size to aid digestion. Here the crow finds a cache of perfect stones and quickly swallows four of them.
Filmed with Canon SX70HS on Amazon at: https://amzn.to/2QftDPd
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Thumbnail photo from cuatrok77 via creative commons license at this link: https://commons.wikimedia.org/wiki/Fi...
Image was cropped and edited.
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