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Archive for October 27, 2011

Ruffed Grouse Crop & Gizzard: the initial steps of digestion

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Some birds, especially those that eat seeds, buds, leaves and nuts, such as ruffed grouse, eat food very rapidly, faster than it can be passed through the digestive system.  These birds usually have a pouch-like crop  where food is kept to be digested later, when the birds  are not out in the open, susceptible to predators.  When the grouse roosts, food leaves the crop and passes through the stomach, which has two parts: a proventriculus – an enlarged area where gastric juices begin breaking down the food, and a ventriculus, or gizzard, which is very muscular, and crushes hard items, such as nuts. According to Roger Pasquier, in Watching Birds, the evolution of an internal means of breaking down food has enabled birds to do away with the heavy teeth and jaws found in fossil birds.  Many birds, including grouse, swallow sand or gravel (you’ve probably seen birds on dirt roads doing this) which passes into the gizzard and helps grind up hard food items.  One photograph shows the contents of a grouse’s crop – bits of leaves, what I think are huckleberries, barberry fruits, buds and a twig—all intact.   If you look closely at the photograph of the gizzard contents, you will see, in addition to crushed fruits and seeds (and two pieces of what appear to be nuts in the upper left) that the grouse recently consumed, tiny bits of sand (upper right) which help in the grinding process.