Klemek’s Minnesota Outdoors: Grit in the gizzard

Submitted by Blane Klemek
Crookston Times

    Anyone that knows a few things about wild birds, and birds in general, is aware that some birds “pick grit”. While some backyard bird feeding enthusiasts go the extra mile to provide grit for their feathered friends, anyone that owns domestic pet birds, chickens and waterfowl included, knows to purchase special mineralized grit and other grit products for birds that are under their care.

    But why? After all, grit is merely small pebbles, bits of sand and stone, and sometimes even small shells. Surely there’s no nutritional value to these items, correct?

    To understand why many species of birds actively ingest grit, one needs to look internally, not to mention having a general understanding of what a particular species of bird’s diet consists of.

    Gallinacious birds such as grouse, turkeys, quail, pheasants, and domestic fowl, for example, eat all kinds of seeds, nuts, and certain fruits with hard seeds inside. Wild turkeys that inhabit forests where walnut trees exist, swallow whole walnuts. Ruffed grouse gulp down acorns, as do turkeys and other species of birds such as wood ducks.

    Seed eaters also include most species of passerines, or perching birds as they are also called, like finches, doves, some corvids, sparrows, and countless other species. These groups of birds consume large quantities of hard foodstuffs, too, and all of these birds—those that need to digest these difficult to break-down foods—also need a little help to do so, both physiologically and, in the case of grit, mechanically.

    So how does grit and physiology work together in birds?

    It all boils down to a specialized two-part stomach, and one part in particular—the gizzard. The first part of a bird’s stomach is glandular, also called the “proventriculus” stomach. This is the part of the stomach where an array of digestive enzymes are secreted into. In fact, this part of a bird’s stomach is very similar to our own. This is also where the digestive process in birds really begins.

    In humans and other mammals, the digestive process, though beginning in earnest inside the stomach, actually begins in the mouth. Food is first broken down as it’s chewed in a process called mastication. Teeth and enzymatic saliva break down food to prepare it for swallowing and passing safely through the esophagus to the stomach. Birds don’t have teeth and are unable to chew food. They simply swallow food whole.

    With some birds such as turkey and grouse and many other avifauna, an internal pouch, also called a “crop”, is located adjacent to the esophagus as an “offshoot”.  A bird’s crop temporarily stores food before passing into the esophagus and to the stomach. As a ruffed grouse hunter, I routinely examine the crop contents of grouse I harvest in order to see what the birds were eating, which can then be used to better understand the type of habitats grouse are using.

    Once the partially digested food passes from the first part of these birds’ stomachs, the food enters the earlier mentioned second part—the gizzard. This unique, powerful, and very muscular organ, the part of a stomach that mammals do not possess, is where seeds, nuts, and other hard foodstuffs are broken down even further. The gizzard is also where grit accumulates.

    As food enter into the gizzard, the muscular organ, along with grit and digestive enzymes, all work in synergy to crush, grind, and break-down nuts and seeds for eventual passage through the intestines for further digestion and eventual passing. Indeed, to hold a large uncracked walnut in one’s hand while imagining anything other than a nutcracker or hammer capable of breaking it, is to know that grit, enzymes, and a gizzard is all that’s necessary for a bird to “crack the nut”. Think of a gizzard and grit as the teeth that birds don’t have.

    While I don’t often write about the internal workings of birds, such topics are no less interesting when compared to the myriad of all the other fascinating features of birds everywhere as we get out and enjoy the great outdoors.