The low, muffled "hoo-hoo" of a great horned owl sounded across our backyard, just as I began to drift off to sleep. The calling seemed to come from a group of large white pines near the back corner of the yard. Through the window, I saw a dark form quietly fly out from the pines, cruise over a neighbor's hayfield and then return.
The owls in our yard sent me looking for information on them. Owls are active at night and make their living by catching and eating other animals. They catch animals with their claws, called talons, and carry them back to their roosts. Roosts are regularly used sites, often located near nests, and are places where owls perch and eat their prey. Owls commonly roost in solitary trees or groups of trees that stand out from the rest, such as large old trees adjacent to fields or stands of pines or cedars in a forest that is mostly hardwoods.
When we eat bony foods, like fried chicken, we use our teeth, a fork or our fingers to remove the meat from the bones. Similarly, owls use their hooked beak to pull flesh from the bodies of larger animals, such as cottontail rabbits. But when a hungry owl catches something small, such as a mouse, it often swallows the animal in a single gulp.
After an owl swallows a mouse, strong acids in the owl's stomach begin to digest the mouse's muscle and other soft parts. The owl can't digest the bones and fur that come along with the meal, so the owl's stomach forms these indigestible materials into tight packages called pellets. Several hours after a meal, an owl will regurgitate one of these pellets. The pellets, along with feathers and other remains, can be found under owl roosts.
Pellets vary in size and shape, but the most commonly found-those from great horned owls-are about 2 to 4 inches long and 1 to 2 1/2 inches in diameter. They are gray-colored, densely packed and lightweight when dry.
To find some pellets, first choose an area where you have seen or heard great horned owls in the past. Then check likely areas for roosts, such as large trees and pine and cedar thickets. Look on the ground near the trees for the white splashes that are the owl's droppings. You may also notice prey remains, such as fur or feathers. Pay special attention to large trees with limbs that are horizontal near the trunk. Once you find white splashes or other obvious signs of a roost, search carefully for the gray pellets.
By looking at the bones, bone fragments, tiny skulls, hair and other materials in the pellets, you can tell what kinds of animals the owls are eating. To open up a pellet, place it in a pie tin or other shallow dish with a small amount of water. Use a pair of old table forks or tweezers to carefully tease apart the pellet and examine its contents.
Like a police detective, you can look carefully at the skulls, jawbones and other items to figure out which animal they came from. Use a magnifying glass if you have one. Try to match the skulls you find to the ones pictured here. Even hairs and feathers sometimes can be identified. The Wild Mammals of Missouri is a good reference for identifying rodents from skulls and other fragments. Look for it in a school or public library.
Great horned owls usually eat mice, voles, shrews and rabbits, but sometimes they eat skunks, muskrats, house cats, weasels, mink, flying squirrels, snakes, frogs and birds. They will even attack and eat other hawks and owls.
Predators, such as owls, are an important part of nature. Owls survive by eating the large number of mice and other animals produced by nature each year. By consuming this surplus, owls help to control some prey populations. But the reverse is also true: a shortage of prey animals limits the number of owls that can survive. This codependency brings about a balance between predator and prey.
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