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05 March 2004

Some Notes on an Owl Pellet

Bill Dembowski

Owls, like all predatory birds, are incapable of chewing their food, so they swallow their prey whole. After they have digested the softer parts, they package the nasty bits (bone, teeth, fur, etc.) into egg shaped masses that are regurgitated on a daily basis. These are known as owl pellets. Dissecting one of these owl pellets is a great way to (1) learn something about the owl and its prey, and (2) get that sense of discovery that we all enjoy so much.

The Pellet Itself

Perhaps the best way to start an investigation of pellets is to buy a 3-pellet kit, which will include some bone identification charts, plastic forceps, and a small magnifying glass. (See sources at the end of this article.) The pellet described here was about 50mm long, 25mm wide, and weighed in at 7.4 grams. These measurements are typical. Pellets look about what you would expect for a chunk of matted fur. They are fumigated and/or sterilized to preserve their natural beauty (bugs will eat anything).

Into the Fur

The process of dissecting an owl pellet can best be described as getting rid of the fur. It is everywhere. It is not only around but in every little nook and cranny.

Try not to get too anxious, however, because some of the bones can be quite fragile, particularly the ribs and those comprising the skull cap. Forceps and round toothpicks work just fine, but I also like to use my fingers to feel for the hard parts. In the specimen studied for this article, I found two skulls, which is not unusual. What is unusual was the condition of the larger skull.

Owls tend to crush the back of the skull during the kill, so finding one relatively intact was a real bonus. Both skulls belonged to small rodents called meadow voles; think of them as field mice if you like. Note the difference in coloration, which is because the smaller skull has been bleached. If you plan on keeping your boney finds, you may want to do the same.

I use a soaking bath of 3% hydrogen peroxide from a supermarket or pharmacy. Some bones will come clean in an hour, others require six or more. Check them periodically, because over-bleaching can be harmful, particularly to skulls and jaws, where it tends to dislodge the teeth.

The teeth of a vole are imbedded in the lower jaw or extracted. I find it interesting that the teeth are not separate entities but are always found in regularly formed clusters.

After the skulls, which are usually considered to be the most interesting objects in a pellet, we are drawn to the larger bones, including the pelvis, femur, and so forth. One cannot resist the temptation to describe them as simply "just like real bones, only smaller."

The vertebrae are interesting in that they come in a variety of sizes and shapes, depending on where in the spinal column they originated. They are the hard little knots that you can easily feel through a tuft of fur. Be careful, though, because the cervical vertebrae (those from the neck) are much more delicate than those from the lower spine. All vertebrae will need to have the fur cleared from their centers before bleaching. The ribs, on the other hand, come clean in a hurry. They are flat and delicate, and a gentle hand will slip them right out of the surrounding fur.

Look a little closer, and you will start to find the small bones of the lower extremities. Here is where a good magnifier or stereo microscope really comes in handy because many will look like fragments instead of the complete bones that they are. Hint: An easy way to handle these little gems is with a moistened artist's brush.

Going Deeper

After I have extracted all of the "easy" bones, I like to examine the mass of accumulated fur with my stereo microscope, a tuft at a time, to see what is hidden in that hairy forest. Then, after teasing out each piece, I tap it briskly on the bottom of the Petri dish I use for dissection, because you never know what might fall out.

The resulting pellet litter will consist mostly of small bone bits, pieces of claw, and other miscellaneous pieces of plant and animal matter. What I like to keep an eye out for is evidence of small arthropods. Keep in mind that the contents of the pellet have gone through some of the digestive process, and any little invertebrates you find may be difficult to identify. Finally, don't forget to examine the fur itself. It shows quite a variety of textures and colors and will make a nice addition to a collection of animal hairs.

Some Suppliers of Owl Pellet Kits

Acorn Naturalists:

http://www.acornnaturalists.com/store/product1.asp?Product_ID=3184

Edmund Scientific:

http://scientificsonline.com/product.asp?pn=3052457

Genesis Inc.

http://www.pellet.com/old/indi.html

And, for those who would like to merely dabble in this sport, here is a web site where you can perform the virtual dissection of an owl pellet right at your keyboard.

http://www.kidwings.com/owlpellets/barnowl/index.htm