“She’s so cute!” a little girl coos to the snowy white owl. The owl blinks languidly, ignoring her admirer. No doubt she is used to human attention, as she is one of the more popular raptors housed at the Vermont Institute of Natural Science Nature Center (VINS) in Quechee, Vermont. She likewise ignores the decapitated rat in her food bowl, chirruping softly as if dissatisfied with what’s on the menu. I wait patiently, hoping to witness the moment when she gulps it down.
Owls eat their smaller prey whole, or tear larger prey into chunks with their beaks and talons. Sooner or later, that owl will grab the raw rat out of her food bowl with her sharp beak and knock it back like a shot of whisky. It will slide down her esophagus and into her two-chambered stomach. The first chamber, called the proventriculus, or glandular stomach, secretes digestive enzymes to break down all the easily digestible parts. Much like our own stomach, this chamber will liquefy the soft tissue (the gooey stuff, including muscle, fat and organs). Whatever isn’t digested in the first chamber, such as the bones, fur and teeth, will pass through to the second chamber, called the gizzard.
All birds have gizzards, although not all birds regurgitate pellets. Some gizzards are larger and stronger than others, adapted to what kind of food a species eats. The gizzard is made of thick muscles that grind down the tougher parts of a bird’s meal, moving all the soft material through to the intestines. Some birds with very muscular gizzards even eat small stones and grit to help grind down bones. In birds that regurgitate, the hard, indigestible material is compressed by the gizzard into a pellet.
Unlike most birds, owls do not have a baglike organ called a crop in their throat, which stores food to be digested later. Whenever the owl eats, she will start to digest immediately. Good thing, too, for the owl can’t eat again until that pellet has been ejected; it takes up too much room in the stomach. Although horking up a packet of bones after every meal might seem uncomfortable, the process is actually thought to be vital for the owl’s health. As the pellet travels up the digestive tract, it scours her throat clean.
Owls often return to the same perches for regurgitation, and you’ll often find piles of pellets lying around the base of a favored tree. At first glance, disgorged pellets look more like scat than regurgitations, as the pellet is squished into the oblong shape of the gizzard. Upon closer inspection, a plethora of tiny white bones can be found, nestled in hair and fur. With patience and a steady hand, the prey’s entire skeleton can be reassembled.
Dissecting owl pellets is an excellent introduction to the complexity of the food chain and predator/ prey relationships. Not only do owl pellets contain the bones of their prey, they are also ecosystems unto themselves, containing fungi, beetles, moth larvae and caterpillar droppings. The pellets carry potentially harmful viruses and bacteria, so if you’d like to dissect a found pellet, you might want to handle it with gloves and put it in the microwave for a minute or so, to sterilize it. Or, a short cut: the Montshire Museum of Science in Norwich, Vermont sells a popular sterilized pellet dissection kit in their gift shop. For bulk orders, VINS collects all the bird pellets from the animal enclosures every day, separates the pellets by species, and freezes them to sell for $1.00 each, mostly to schools and nature camps.
Back at the enclosure, I wait and watch the owl as she sits on her post, still ignoring the rat. Born and bred in captivity, she evidently has none of the urgency of a wild bird to secure its next meal. Slowly, her beautiful white head turns, and piercing yellow eyes blink.
I see you.
I stare back. She tilts her head and trills low in her throat. Then her head casually swivels away, dismissing me, and at least for now, her dinner, as she fluffs her mottled feathers to settle back on her perch.