For owls, what goes down must come up
With not a lot of wildlife or plant activity going on this time of year, I often look to the detritus on the to see if something interesting catches my eye. Not long ago I came across an oval-shaped wad of fur that I’ve wanted to come across for years — an owl pellet.
The wad of hair was about two inches long and oval. On closer inspection, I could see a bone fragments mixed in with the hair. If it is indeed an owl pellet, it probably came from an eastern screech-owl (Megascopsasio) that’s been doing its distinctive whinnying call down in that area for months.
Raptors, such as owls, and a few other bird species deal with the nondigestible parts of their prey — including bone, teeth, hair, feathers and exoskeletons — differently from most birds. Most birds, including other raptors, also have a crop, which is a food-storing pouch that is created by the expansions of muscles in the esophagus, owls do not. But eastern screech-owls can cache food in tree holes for as long as four days, according to All About Birds (tinyurl.com/wiscreechowl), a Cornell Lab of Ornithology website.
With owls, the food goes directly to the gizzard, at the rear of the stomach, which is an organ unique to birds. There digestive fluids, mixed with hard, rough materials such as small stones the bird has picked up, dissolve and grind up the food. The soft tissue is then sent to the intestines to be further broken down and the nutrients absorbed. Small amounts of tissue that is not absorbed, along with other bodily waste, is excreted through the owl’s vent, in its rear end.
The larger indigestible parts of the prey are formed into a slimy pellet, which through strong contractions in the gizzard, the owl expels out of its mouth. This process is known as “egestion,” which is unique to birds. It differs from the regurgitation process of mammals, which comes from the contraction of abdominal muscles. Owls generally feed early in the evening and expel a single pellet about 20 hours later.
While the process does not sound pretty, the pellets are like little treasure chests for the nature-curious and sterilized pellets are used in schools to teach kids about what owls eat. Although most bones are usually preserved, they are often mixed with parts of other prey.
With eastern-screech-owls, the diet is quite diverse, according to All About Birds: Most kinds of small animals, including mammals such as rats, mice, squirrels, moles, and rabbits and even bats are on the menu. Other prey include small birds, such flycatchers, swallows, thrushes, waxwings, and finches, as well as larger species, including jays, grouse, doves, shorebirds and woodpeckers, sometimes stripping off feathers before consuming the rest. Even identification bands for birds have been found in owl pellets.
Eastern screech-owls also eat “surprisingly large numbers” of crayfish, frogs and tadpoles, lizards, along with insects, earthworms and other small invertebrates, according to All About Birds. In fact, “data from pellets may underestimate the number of soft-bodied animals, like worms and insects, the owl has eaten.”
This screech-owl is small (6-10 inches) and quick. It often sits silently on low tree limbs watching for prey or roosting there. On several of my wanderings through forests, I’ve been surprised to turn and find myself staring into the eyes of a screech-owl sitting on a branch just a few yards away. They always seem unruffled, usually just blinking and staring back.
Screech-owls often nest near humans, perhaps hoping to pick off small birds at feeders, or the rodents that come after seed that falls from them, as one was apparently doing on my deck one evening last year. The eastern screechowl’s sense of hearing is “so acute that it can even locate mammals under heavy vegetation or snow,” All About Birds adds.
When I finally got around to opening my present, I didn’t find what I’d hoped to find — a complete set of rodent bones — but rather a mix of tiny bones, bone fragments and some other unidentified detritus, perhaps from invertebrates. Owl pellets sometimes do have few bones, or none, but I’d love to find one with a complete skeleton to reassemble and, to that end, I keep checking out the area where I found the first pellet.