Laura Erickson's For the Birds

I just spent a day with some fifth grade girls, dissecting what William Proxmire disparagingly dismissed as “owl vomit.” Every day owls regurgitate one pellet, a tightly packed bundle of the bones, fur, teeth, and other indigestible items from the previous night’s meals. As in dogs and cats, if bones broke apart and got into an owl’s intestines, they could perforate it, killing the owl. To prevent that, the indigestible parts get bound up within the muscular chamber of the stomach, called the gizzard. And the owl spits out this little bundle as solid evidence of every single creature it killed in the past 24 hours–something crime labs and prosecutors can only dream of.

I’ve been working with girls on owl pellets and other things about birds in a week-long program called Fast Camp, designed to encourage girls to get interested in science. We got our pellets from a biological supply house to ensure their safety-sometimes what looks like an owl pellet is in fact fox scat–not a healthy thing to handle. Real owl pellets are completely safe to work with unless the owl happened to eat a mouse infected with the hanta virus, which isn’t killed in the stomach. Fortunately, biological supply houses sterilize their pellets in an autoclave, killing the hanta virus and any other germs that might be there. Each pellet is wrapped in a piece of aluminum foil, and the girls take turns reaching into a plastic bag to pull out their pellet with the anticipation of a child just about to open birthday presents.

Of course, beneath the aluminum foil wrapper, owl pellets look rather brown and yucky, like a Baby Ruth candy bar that’s been rolled in fur. The girls use toothpicks, forceps, and probes to tease them apart, and painstakingly extract bones and teeth from the felted fur. The pellets we get come from Barn Owls, and are a couple of inches long by about an inch in diameter, but as they’re teased apart, the fur ends up taking up a surprisingly large volume.

Most of the bones remain perfectly intact in pellets, and it’s both gratifying and fun to watch the girls as they discover just how fascinating they are. A rodent skull alone is fascinating. Girls can see the brain case, with a clean hole in back where the spinal cord originates, the large eye sockets, the big holes where the powerful chewing muscles run through, and the strong front teeth–orange in many species, and extremely long. The back teeth are exquisitely tiny. In microtene rodents like the meadow vole, the molars look as if they were made by a sharp, thin ribbon folded in and out on itself and squeezed together in a beautiful pattern, a design giving the teeth an enormous amount of surface area for biting, with the sharpness necessary to grind up silica-encrusted cell walls of grasses so the voles can get the nutrition within. Rodents with a more varied diet have more normal-looking molars.

The lower jaws have incisors and molars that match the upper ones, and widen in the back to provide a substrate for the huge and powerful chewing muscles that mark the rodent family. The girls can clearly see how bones from all over the body are designed to accommodate muscles and nerves.

Just about every Barn Owl pellet has at least one rodent skeleton in it, but it’s the additional bones that make each pellet unique. One girl had a fairly intact skull from a small bird-based on the shape of the beak, it looked like it may have been a phoebe. There were a couple of shrew skeletons, one mole, and one girl found the wing casings of a ladybug. Owl pellets teach fascinating things about owl digestion AND about small animals, and identifying the species within them is one of the best tools biologists have for assessing rodent populations in a given area. All this, and they’re darned fun. Some of the girls had felt a bit squeamish to begin with, but within minutes they went from being grossed out to engrossed.