Scientists believe that the barn owl originated as a dweller in high clay cliffs of Europe and this may be one reason why the birds prefer the vertical walls of manmade structures even over trees. There may be other advantages in "owning" a barn, particularly in the winter. Long periods of heavy snow can result in high mortalities in barn owl populations since their prey is too far beneath the snow to catch. But a barn may provide an available supply of rodents during these periods, allowing the resident barn owls to survive.
Highly successful, the barn owl spread through all the known continents, and morphed into 35 subspecies, some of them confined to single island chains. The two best known races are the Barn Owl of Europe, Tyto alba alba, and the North American Barn Owl, Tyto alba pratincola.
Barn owls share a number of traits with other owls: large eyes, well-developed facial disks, soft feathering for silent flight, cervical bones that allow the head to turn 180 degrees, and four sharply clawed toes, one of which can be turned forward or backward.
Barn owls are medium sized owls, standing approximately 10 to 12 inches high, and despite their size, they are exceedingly light, weighing about a pound (454 grams).
Although female barn owls tend to have darker plumage and males tend to be whiter, this is only a generality and not a surefire way of determining sex.
Although the barn owl can not see in total darkness, it can still fly very well in darkness so dim that a human could not navigate.
They can hear so well that they can hunt with high accuracy in total darkness by homing in on the footsteps and nibbling sounds that rodents make. Some researchers believe that they can actually tell what type and size of rodent they are hearing.
The reason that barn owls bob and weave their heads is to gain depth perception
Although they are most noted for their high-pitched scream, barn owls produce a number of sounds: from the hen and young “snoring” in the nest to chirps, twitters, and tongue clicks—some used for bonding, begging for food, mating rituals, and danger warnings.
Barn owls typically hunt three times per night: near dusk, midnight, and dawn. These are the best times to observe them on the wing.
BREEDING AND DEVELOPMENT
Although they are strongly associated with nesting in barns, these owls also will use hollow trees, and in the western United States will nest in gullies and have even been known to hollow out a bank with their feet.
Eggs are dull white and elliptical, and are usually laid at two to three days intervals. Clutch size is often large for a raptor—up to 13 eggs have been found in one nest, and 11 chicks in another. Three to seven is more common.
Eggs take between 29 and 34 days to hatch.
The eyes of the chicks remain closed for about 12 days.
The young take approximately 8 weeks to fledge.
Quills emerge at around 13 days.
At 28 days, the tail feathers emerge and the iris turns from yellow to brown.
By 35 days, the birds begin to wander around the nest; the eldest may peer out of the entrance hole.
The young begin to wander from the nest between 5 and 8 weeks old, but generally can not fly well until their 8th week.
Once fledged, young barn owls suffer a high mortality—studies have consistently shown between 60 and 80 percent perish in their first year.
Fledglings in the northern United States tend to disperse wide and far before the winter—some birds travel over a thousand miles, and the predominant direction is south. In the spring, some birds show a tendency to return toward their natal area.