Barn Owl Natural History
The Natural History & Breeding of Barn Owls in Northern California
Barn Owls are found all over the world—on every continent except Antarctica. There are 16 known species. In some parts of its range the barn owl is gravely endangered, including Britain and parts of the Midwestern and Eastern United States. The Barn Owl requires a cavity, ledge, or old building in order to raise a family. They will also use artificial nest boxes, as will Screech Owls. Owls do not build nests! Other owls, species that are not cavity nesters - such as the Great Horned Owl, will take over the vacant nests of other large birds, such as hawks and ravens. Owls mostly swallow their prey whole, and approximately 12 hours later they regurgitate a pellet consisting of the bones and fur of their last meal. These pellets, when deposited in the Barn Owls nesting area, create a soft, warm carpet upon which to lay the eggs. They also provide researchers with a clear picture of what the owls are eating. From the study of Barn Owls, and their pellets, it is known that these owls are amazing consumers of rodents and thus extremely beneficial to the environment. In locations where owls have roosted for years excellent studies can, and have, been made of their lives and their diet. Although rodents, such as rats, voles and gophers, are the favored food, the barn owl is opportunistic and will also eat songbirds and other creatures. A family of Barn Owls can consume about 1300 rats per year and 3000 rodents in a breeding season alone! It is for this reason the U.S. Fish and Wildlife Service stated that the barn owl is the most economically beneficial species to humans.
Barn owls form their own species, separate from other owls, called Tyto. The Common Barn Owl is Tyto Alba. The plumage of barn owls is quite variable, but all have a disk-shaped face that is said to resemble a heart. This disk is not decorative—it performs an important function. The owl's ears are placed asymetrically on the sides of its head. The disk around the face helps to funnel sound into the owl's ears and allows it to zero in on the exact location of prey - even in total darkness. They have the best hearing of any animal tested. The Barn Owl's face can be thought of as the outer part called pinnae) of its ears with the sole purpose of directing sound into the ear openings. Barn owls are capable of locating and capturing prey solely by sound, although they also have excellent night vision. This "satellite dish" on the Barn Owl's face is so important it has a unique accessory that no other owl has: a special "comb" on one toe of each foot, which is used to comb the disk and keep it in good shape. This is called the pectinate claw.
The Barn Owl's body is a golden brown on the back. The breast can be a variety of shades from white to golden brown and is usually speckled. Male barn owls are thought to be much whiter on the breast, with fewer spots, than females. Females, as in most birds of prey, can be larger than males. Barn Owls have a long bill and small, dark eyes. The bill doesn't appear very large because it is hidden under feathers, but the mouth can actually open very wide, not unlike a snake's mouth, allowing it to consume large prey items whole.
Barn Owls have long legs and large talons. In flight, they are completely silent and fly down and kill their prey very quickly—usually without the prey ever knowing they are coming. This is because owl feathers have an uneven leading edge that is serrated - air passes through the feathers so their wings don't make a sound in flight. Barn Owls are exceptional hunters, and when feeding their nestlings will consume thousands of rodents in a season. In the past many farmers shot the owls fearing for their poultry livestock, but today many have come to realize that the owls perform a valuable service in their control of rodent populations. Many ranches, farms and vineyards now encourage owls to take up residence by installing owl boxes and ceasing the use of rodenticides (poisons), which cause secondary poisoning when poisoned rodents are consumed by birds of prey. View a CNN Report on farmers in Florida using Barn Owls to protect their crops.
Barn Owls are known for their tolerance of humans as they often choose to nest in quite close proximity. Sadly though, it is humans who cause a great deal of the barn owl's mortality. The owls natural enemies include the great horned owl which will hunt other owls. There may also be predation of young and eggs by large snakes, raccoons, and squirrels. Most Barn Owls live very short lives—only 2-3 years. As is the case with all wildlife, over 50% will not survive their first year of life. This will be due to starvation, predation by Great Horned Owls (aka the Tiger with Wings), and damage caused by humans such as car strikes, shooting, secondary poisoning, and destruction of nests and habitat. Perhaps because of their high mortality rate, Barn Owls tend to have large families.
A Great Horned Owl has 1-3 chicks, but a Barn Owl can have from 2-11 chicks in a nest. They also sometimes "double clutch." This simply means that after raising a family of owls, if food is plentiful, they may nest again and raise a second family. Because they nest in cavities, their eggs are pure white as no camouflage is required. In some parts of California Barn Owls nest year round—in some very unsafe places. WildCare & the Hungry Owl Project have rescued owl babies who have fallen from palm trees (they nest at the top on the ledges under the fronds), bridges, industrial garages, and a milling company, among others. See our News page for stories of our rescues.
Breeding season generally starts in January, February, or March, depending on weather conditions, with the male looking for a suitable nest site. Once he has found a site and moved in, he tries to attract a mate. Courtship behavior begins 6-8 weeks before laying the first eggs. The time of year varies depending on weather and availability of prey. Activity is centered in and around the nest site. Some existing pairs may have roosted together at the nest site over the winter, but most roost apart—males, in particular, roost away from the nest. Males start spending more and more time at the chosen nest site at the beginning of the breeding season enticing their partners into the box. Once the female has accepted a mate, and is ensconced inside the box, she becomes more and more "broody" and she stays in the box for extended periods of time. Before mating, the male presents her with food. Once egg laying and incubation begins, the male continues to mate with the female and bring her food.
In Marin County, 5-7 eggs are laid at 2-3 day intervals, usually around March. Eggs hatch after about a month—one-at-a-time, every 2 to 3 days (asynchronous hatching), so the owlets can differ in age by as much as 2 weeks. Sometimes the youngest owlets do not get enough food and die. They will be consumed by their siblings as they are now food. The male will continue to bring food to the female throughout the incubation period and until the owlets are a few weeks old. At that time, both male and female hunt ceaselessly to provide food to their voracious offspring—sometimes flying for miles and even hunting by day if necessary.
For owls that are using barn owl boxes, the first signs of an occupied box might be frequent calls around the box at night, scratch marks around the box entrance, or a white ring of feather powder around the box entrance. Another sign might be "white wash" in the vicinity - this is splashes of what looks like white paint, but is actually the fecal matter of the owl. The drainage holes in the bottom of the box may appear blocked if in use because the pellets form a soft substrate in the bottom of the box. It is very important NOT to disturb the box at this time as the females may abandon the nest even if already incubating eggs. If your box is on a pole, avoid touching the pole as any vibration could cause the female to take flight.
This photo of a Barn Owl leaving its box was taken by our friend Phil Johnson. This could be a male Barn Owl because the breast is very white. Hunting is the #1 activity of the Barn Owl and is also when it is most vulnerable. Many Barn Owls are hit by cars while hunting because one of their hunting techniques is to fly low, around 10', over the ground listening with their amazing hearing for the sounds of rodents. If a road happens to cross the fields where the owl hunts, the owl can easily be struck and killed.
If you believe you have a pair of owls nesting in your box, please call HOP at 415-454-4587. We will be banding babies again this Summer for our research. Like all birds of prey, Barn Owls are protected by Federal & State laws, and once they have begun nesting in a box, it is illegal to disturb them.
If you find a baby owl on the ground, please call your local wildlife rehabilitation center. In Marin County, call WildCare: Terwilliger Nature Education and Wildlife Rehabilitation at 415-453-1000, or the Marin Humane Society at 415-883-4621. If a cardboard box is available, it can be placed over the owl to keep it safe, and to reduce stress until help arrives. Please refer to Baskets for Birds for more on how, and when, or if, to pick up a raptor that is on the ground. Juvenile owls are capable of climbing into and around trees using their sharp, taloned feet. Never attempt to handle a bird of prey without wearing heavy gloves.
Barn Owls have many vocalizations, some quite frightening and eerie. Listen to a Barn Owl (tyto alba). Often times people will think that Screech Owls are living nearby because they hear screeching sounds during the night. In fact, Western Screech Owls don't really screech at all! Listen to a Western Screech Owl (Otus kennicottii). They have soft, descending hoot. The hooting sound that people identify with owls is the Great Horned Owl. Listen to a Great Horned Owl (Bubo virginianus). Barn Owls are the ones doing the screeching. They also hiss, scream in a bloodcurdling way, click and clack their beaks, and make many other strange and wondrous sounds. Baby owls will spend the entire night calling for food with a sound that is hard to describe. Some have compared it to the sound of steam going through pipes, or the sound of an Espresso machine steaming milk, or simply a hissing sound.
VOCALIZATIONS: Fifteen vocal and two nonvocal sounds were described by Bunn et al. (1982). B. Colvin (pers. comm.) described the five most frequently heard vocalizations: 1) the "contact call" is a drawn-out screech frequently given in flight when approaching a nest site from a distance; 2) the "alarm call" is an intense screech made in response to human or other disturbance which is typically given at a nest site and only after chicks have hatched; 3) "squeaking/ticking calls" are rapid, high-pitched notes which are associated with pair bond maintenance or distress situations; these calls are commonly produced during courtship, incubation, and first evening flights after chicks have hatched; 4) "snoring" is a greatly varying hiss which is repeated persistently by juveniles in and out of the nest; this call is used for food begging and may be heard at nest sites from sunset to sunrise; and 5) the "defensive hiss" is a very loud and prolonged hiss typically produced by nestlings when disturbed. (Source: The Nature Conservancy, Species Management Abstract. Contributing Author(s): Rosenburg, C.; revisions by G. Hammerson, M. Koenen, and D.W. Mehlman).
Barn Owls resemble giant white moths floating buoyantly through the night sky, and seem to disappear at times before your very eyes. With their screams, silent flight, and white appearance it is not surprising that through the ages Barn Owls have been associated with the supernatural. In some Latin American countries they are thought to associate with witches and are sometimes persecuted. In reality, Barn Owls are harmless (unless you are a rodent), beneficial beings who grace our world with their beauty and eternal mystery.
All content and photographs copyright The Hungry Owl Project and respective photographers: Andy Harmer, Don Freundt, and Phil Johnson.