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Look Who Nests in Nest
Boxes....Screech-Owls
These small, secretive owls may be living near you When most people think about birds nesting in their backyard nest box, bluebirds, swallows, or wrens probably come to mind. And these are certainly a few of our favorite nest box occupants. But other, less-familiar birds such as screech-owls also use the nest boxes we provide. These owls use cavities for nesting, roosting, and storing food during winter. Because they do not excavate their own cavity, instead adopting natural cavities or abandoned woodpecker holes, the size of screech-owl populations in some regions is dictated by the number of available cavities. As forests are cut, the number of natural cavities decreases, and the importance of supplying artificial cavities--nest boxes--increases. The Cornell Nest Box Network (CNBN) encourages citizen scientists across North America to provide nest boxes for screech-owls and to collect data about these lesser-known cavity nesters. Read on to learn more about these small, secretive owls. Appearance Eastern (Otus asio) and Western screech-owls (Otus kennicottii) are small owls, about eight-and-one-half-inches tall, that closely resemble each other. They were formerly classified as one species. Eastern Screech-Owls, which are found from east of the Rocky Mountains to the Atlantic Ocean, have three color morphs--rufous, gray, and brown--that occur throughout the range. Western Screech-Owls, which inhabit the western coast of the continent, are usually gray, although some individuals along the northwest coast are brownish in color. Habitat and Diet Screech-owls live in a variety of forested areas, preferring woodlands interspersed with open clearings, meadows, and fields, which they need for hunting. They also inhabit wetlands, orchards, suburban parks and gardens, and towns. The western species is also found in deserts. They have the most varied diet of any North American owl, feasting on insects, crayfish, earthworms, and all classes of vertebrates, including songbirds, fish, amphibians, and small mammals such as shrews, rabbits, bats, and rodents. Screech-owls cache uneaten prey in cavities. Nesting Female screech-owls select a nest site--usually an abandoned woodpecker hole, hollow stump, or hollow tree limb--from the cavities on the male’s territory. Western Screech-Owls also nest in saguaro cactus cavities. Both species use nest boxes, and they select boxes as often as they choose natural cavities for their nest sites. Screech-owls do not build nests; instead, they form a depression out of the fur and feathers of the prey they have eaten in the cavity. Eastern Screech-Owls lay three to four eggs in a clutch, and Western Screech-Owls lay two to five eggs. The slightly glossy eggs are white to creamy white in color. The incubation period is 26 to 30 days for Eastern Screech-Owls and 21 to 30 days for Western Screech-Owls. Only the female incubates the young, but the male delivers food to her throughout this period and for the first two weeks after the young hatch. After hatching, the female broods the young but stops after 6 to 13 days, when the young can regulate their own body temperatures (also known as thermoregulation). Both parents then care equally for the young, protecting them and providing food. After about 28 days, the young leave the nest, but they can only climb and hop from branch to branch. As they grow older, they make longer flights and begin to hunt, becoming completely independent 8 to 10 weeks after leaving the nest. Screech-owls raise one brood per breeding season. After the Breeding Season Screech-owls do not migrate; they maintain home ranges throughout winter. Pairs occasionally roost together during winter in hollow trees, nest boxes, and evergreens. What Can You Do? Both Eastern and Western screech-owls compete with other species--honey bees, fox squirrels, and Northern Flickers--for natural cavities. You can provide nest sites for screech-owls by putting up nest boxes. Screech-owls use the same type of box used by American Kestrels. The box should have a three-inch entrance hole and the following approximate dimensions: an 8-by-9-inch floor and an interior height of 16 inches. Add 2 to 3 inches of wood shavings to provide material on which the female can lay her eggs. Attach the box to a tree or post at a forest edge adjacent to fields or wetlands. Boxes should be placed 10 to 30 feet off the ground and, if possible, under a tree limb. Monitor the box regularly to ensure the box is not vulnerable to predators and has not been taken over by European Starlings. For more information on providing nest boxes for screech-owls, contact the Cornell Nest Box Network. |
