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Posts tagged “Crop

Mourning Dove Remains

3-13-13 mourning dove remains IMG_5958A cooper’s hawk made short work of a mourning dove near my bird feeder recently, killing and apparently, given the large number of feathers scattered on the snow, plucking the dove on a nearby snow bank. If you look closely you can see whole sunflower seeds in amongst the feathers. These came from inside the mourning dove’s crop. Mourning doves generally feed quickly, filling their crop with seeds which they digest later, when they’ve found a safe spot in which to roost. Unfortunately for this particular dove, it didn’t live long enough to have that opportunity.


Avian Digestion

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What happens to food after a bird swallows it? It may be stored in their crop, a pouch which is actually an enlarged part of its esophagus that some species of birds (and bees, fish and earthworms) have, or it may go directly to their stomach.  Birds have a two-chambered stomach.  The first chamber, the proventriculus, secretes acids that help break down food, including bones. A shrike’s well-developed first stomach chamber can digest an entire mouse in only three hours!  From the proventriculus the food goes into the second chamber, which is referred to as the gizzard, before entering the intestines.  The gizzard is a muscular organ which grinds up tough food, sometimes with the help of grit that some birds ingest.  The gizzard grinds the gravel and stones against the nuts and seeds, a process which smashes the food.  Wild turkeys can actually pulverize walnuts in their gizzards!  In some species, the gizzard remains small and insignificant during the summer when their diet consists of soft food such as flesh, insects, or fruit, but it grows more powerful during the winter when seeds are their main food.


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.