Pellets are made from the parts of a bird’s meal that cannot be digested. Raptors, sparrows, herons, and corvids produce pellets when they eat something that contains hard parts such as fur and bone. Pellets are coughed up and expelled though the beak. While many different species of birds cough up pellets, owls are by far the best type of pellet to dissect because they do not digest bones.
What’s in a Pellet?
The image below shows parts of undigestible bits of rodents (mice and rats). The pellet (regurgitated by a barred owl) is the yellowish/white mass at the top. Below the pellet is a piece of bone; below that, part of a rat leg; to the left are bits of fur and bone.
Opening up a pellet is good way to know what a bird has eaten. Claws, vegetation, feathers, parts of insects, and teeth are other undigestible parts that can be found in pellets.
Why are Pellets Formed?
Pellets are formed because the proventriculus cannot digest the hard parts of a meal along with the ventriculus (the gizzard). The meat, organs, skin, and other tissues are passed along to the intestine from the gizzard. Everything else gets regurgitated.
How Does it Happen?
Simply: a bird finds food (i.e., an insect, rodent, other bird, etc.) and gobbles it up.
The meal then goes through to the esophagus, to the crop (the part of the esophagus where some birds store food), then to the stomach. The stomach is made up of two parts, the proventriculus and the gizzard.
The gizzard is the part of the stomach where a meal is ground up. The parts of the meal that are not passed on to the rest of the digestive tract form a pellet (or casting) in the gizzard. The rest of the meal is passed through the vent.
Studying pellets helps ornithologists understand avian diets and food sources. Finding pellets in the wild is easy. They can be found in many places at the base of trees where birds may roost.
Pellets can contain contagious diseases, therefore, when handling pellets it’s important to wash hands, wear gloves, and sterilize before handling.
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