sites. Today, they are most commonly found in out-of-the-way corners of barns, silos, grain bins and attics.
Barn owls do not construct nests; they simply lay their eggs in a small depression scraped in loose substrate. If loose material is not present, eggs will roll away from each other and fail to hatch.
Barn owls may lay up to 11 eggs, although the normal clutch size is four to seven eggs. The female begins incubation when the first egg is laid, unlike most other birds, which delay incubation until the last egg is laid to cause simultaneous hatching. Barn owls lay subsequent eggs every two or three days.
Eggs hatch after 21 to 24 days of incubation. However, because the last egg may be laid a week after incubation began, the female may have to incubate for 32 to 34 days before all eggs are hatched. For comparison, chickens incubate their eggs for 21 days and turkeys for 28 days. Males bring food to incubating females.
This incubation strategy results in siblings occuring in stair-step ages. The first owlet may be 6 to 18 days older than its youngest nest mate. This age difference is visible in the varying size and plumage development of nestlings. Young owlets may still be covered head-to-toe with a short, white down when the oldest nestling, with plumage resembling that of an adult, is ready to fledge. Young owls fledge when they are about eight weeks old.
Parent owls keep busy feeding themselves and their hungry owlets. Each adult consumes the equivalent of a large rat every night. Each owlet would eat up to a dozen mice per night if given the opportunity.
With a normal nest containing six young, parent birds must capture up to 74 rodents nightly. To capture such a supply of food, adult owls may travel three miles. If they do not catch enough to eat at night, barn owls will hunt during daylight.
Bones, fur and other indigestible parts of prey are compacted into pellets (oblong, dark objects about 2 inches in length) and regurgitated. Biologists examine the skulls in the pellets to identify the kinds of animals owls are eating. The enormous quantity of pellets littering a nest area testifies to the amazing number of rodents a family of barn owls consumes. The presence of pellets is one of the first clues that barn owls are using a building.
The staggered ages of barn owl nestlings increase