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Species profile: The ghostly hunter, Barn Owl
Working the graveyard shift with a Barn Owl family
Published: July 1, 1991 Mice were running races on the rooftop. The stillness of midnight amplified the sound on the granary's wooden shingles, until it filled the hollow darkness of the rest of the barn. The rodents' progress could be traced along the eaves to the end of the roof, then up to the roof peak and down the length of the barn again. But the starlight game was charged with danger. I listened expectantly.
A thump on the roof brought 20 seconds of deathly silence. A second thump, this time directly overhead, was greeted by a sharp chorus of hungry hisses at my feet. On the granary floor, seven owlets strained for position at the imminent feeding.
I was photographing the Croft, Kansas, nest from one of three blinds in the owls' granary home. Various strobes and cords adorned the floor and ceiling, making instant daylight with each click of the shutter.
By the dim glow of a red light I used to illuminate the nest, a limp mouse appeared through a hole in the ceiling, followed by a ghostly face. In a whir of white wings, the adult dropped into a melee of beaks and claws, shrieks and hisses. The Barn Owl had returned to feed its young.
It was June 28, and the clutch of owlets was growing rapidly. The late date wasn't surprising, since Barn Owls nest almost any time of year and sometimes double brood. Eggs and young have been found every month of the year but January, distinguishing Barn Owls from other raptors.
Barn Owls are unique in other ways as well. Adults are white underneath and "monkey-faced." Their eyes are brown and smaller than those of other owls', which are typically yellow. Their strange appearance and their use of old buildings are the source of many haunted house stories.
Though adult Barn Owls may live 20 years, the average life span seldom exceeds four. Sexual maturity is reached early, and nesting may begin before Barn Owls are a year old. Longer-lived raptors such as eagles don't nest until four or five years of age.
Besides reproducing at an earlier age, Barn Owls also differ from most raptors in the number of eggs they lay. Five or six eggs per clutch is common, but there may be as many as 11. Larger owls, such as Great Horned and Barred owls, typically lay only two or three eggs per nest.
Young Barn Owls are an odd assortment, due to their staggered hatching schedule. Most birds lay a full clutch of eggs before starting incubation, so that all hatch at once. But Barn Owls begin incubation as soon as the first egg is laid. Eggs are then laid at two-day intervals until the clutch is complete. The female incubates the eggs for 32 to 34 days.
Hatching occurs over a two-week period, creating a large spread between the oldest and the youngest. This poses no problem unless food is scarce, in which case the youngest owlet may starve or be eaten by an older sibling.
Nestling Barn Owls have voracious appetites and typically consume 100 rodents apiece before fledging. This keeps their parents busy. A large brood may require more than 1,000 feedings during a nine-week period. But Barn Owls are well equipped for the job. They are excellent hunters: one owl is thought to equal seven cats in its ability to destroy mice. Their vision is excellent by day and night, but it's their remarkable hearing that allows them to strike their prey in total darkness.
Ears are set asymmetrically on a Barn Owl's head, so it hears the same sound from slightly different angles. This provides audio depth perception and allows accurate gauging of strikes even when the owl can't see. The Barn Owl has such an acute sense of hearing that it can detect the movements of a mouse from 30 feet away.
As I watched from my blind, the female owl dropped her prey, and a cloud of dust arose from the nest as the young birds fought for dinner. I pressed the shutter as the adult took wing, freezing her in mid-flight by three carefully aimed electronic strobes. After she squeezed through the small hole in the granary's roof, I stepped around the corner to observe the odd youngsters.
They were half-grown now, and a pile of regurgitated pellets — largely consisting of hair and bones — surrounded them on the cement floor. The odor of ammonia and uneaten prey made the nest a foul-smelling affair, but the owls' fascinating behavior took my mind off this unpleasant reality.
Typically, the first feeding each night occurred near full darkness, always announced by the thump of a parent landing on the roof. During my 25 nightly observations, I noticed that prey items varied widely, but all were representative of the central Kansas prairie. The most common were kangaroo rats, cotton rats, deer mice, prairie voles, cottontails, and gophers. Unusual prey items included a juvenile Red-winged Blackbird, a Lark Sparrow, and a meadowlark. One thirteen-lined ground squirrel was also brought to the nest, unique because this rodent is considered exclusively diurnal.
The Barn Owls' hunting areas include several hundred acres of weedy, fallow ground and pasture, a country road whose ditches were colonized by kangaroo rats, and a nearby grain elevator complex which supported a variety of rodents. Most of the hunting was probably done within a mile of the nest, though Barn Owls may travel up to four miles in search of food.
Windy nights made hunting poor. The noise of the wind covered the sounds of prey, and blowing vegetation disguised their movements. Calm nights allowed Barn Owls to hunt with greater success. Adults returned with prey every 10 to 15 minutes. Though the male reportedly assumes most of the feeding chores, both parents shared these duties throughout the nestling phase at this nest, with the female bringing food most often.
Barn Owls generally hunt on the wing, sweeping low to the ground in zigzag fashion. When prey is spotted, the diving owl often emits a terrifying scream which paralyzes the victim with fear for the instant the owl takes to strike.
The owl seizes the victim in its claws and bites its head with its powerful beak before returning to the nest. The same scream, which can be heard more than half a mile away, is sometimes used to alert the nestlings of returning food. A porpoise-like chattering call is also used by adults when closer to the nest.
The feeding schedule was dictated by the owlets' demands. Hunger was expressed with loud, slurping hisses repeated every few seconds. On a calm night, I could hear these calls through the granary walls from a hundred yards away. The parent owls could no doubt hear them from much farther away.
Beginning at dusk each night, the young called incessantly for food. But after several hours of repeated feedings, the calls gradually subsided. By 1 a.m. the seven owlets were usually full, and often slept quietly for several hours. Begging and feeding then resumed until dawn.
The granary afforded excellent protection for the nest. A small hole in the roof served as the only entrance, effectively excluding all predators, such as Great Horned Owls, raccoons, and foxes which commonly prey on owlets. The building was warm and dry, and the crude nest was situated in a bin corner on the dry floor.
As the nestlings grew, they had ample room to practice flight in the granary. Even so, they couldn't escape through the hole in the roof until they were expert fliers. Hunting skills were also learned and sharpened, since the granary was full of mice.
So secure was the nest that the adult owls roosted a mile away in a larger barn during the entire nestling phase. In normal cases where there is danger of predation, parent Barn Owls spend daylight hours with their young, should defense be necessary.
This separation made an ideal photographic opportunity. Preparations, including blind construction, flash placement, and some structural modifications to the building, could be carried out during the day without alarming the adults. By their arrival time each night, all was in order.
As an owlet gobbled down a mouse, I climbed back into my blind, sweltering in the 90-degree heat, and waited for the next return. Fifteen minutes later, the male returned with a Norway rat, probably snatched from the nearby grain elevator. After the usual fight between oldest owlets, the largest won and stalked off to eat the prey.
Mice and other small food items are easily swallowed by young Barn Owls, but larger prey result in a comic struggle. With head tilted backward, the owlet makes vigorous gulping motions, gaining an inch at a time, then resting for a minute. This strain-and-rest approach may continue for 10 minutes or more, until the prey is swallowed or the owlet is forced to quit trying. It's not uncommon for a young owl to sit for half an hour with a rodent's tail dangling from the corner of its bill.
The rat proved to be too much for the small owl, and after partially swallowing it, the young bird grasped the protruding portion with a talon and pulled the rat out of its throat. Immediately, another owlet seized the prey and went through a similar routine. At the next feeding, a parent tore apart the large morsel so that it could be eaten.
As the owls grew larger, they gradually gained the coordination to grasp their prey and tear it apart bit by bit. Appetites were amazing, with each youngster consuming several rodents a night. However, as the owls became able to eat larger prey, their diet of mice, common in the early nestling period, seemed to give way to larger prey, which meant fewer hunting trips for the parents.
Another change at feeding time, which I observed on several occasions, was the presentation of live prey. Such an event provided the young owls with another opportunity to practice their hunting skills. In one instance, a gopher, whose back was apparently broken, was left for the owlets to kill. The gopher appeared lively, but was unable to flee the nest. Unsure how to proceed, the owlets took turns trying to dispatch the victim, without success. For nearly two hours, the young owls watched the gopher with great fascination. Finally the adult female owl killed the animal and ate it herself.
It was 12:30 a.m. now, and the male suddenly appeared with a young cottontail. After a tug-of-war, the oldest owlet covered the prize with spreading wings and ate it in the manner of an adult. Starting at the neck area, the owl ate the intestines and organs first, following with the muscles of the back and front quarters. The hindquarters were swallowed whole.
Watching the young owls every night was a vivid lesson in predation. Though it was grisly to see them tear their bloody meal from a lifeless rabbit, that is precisely the owls' role in nature. Soon this brood would join the ranks of nature's hunters, keeping in balance the abundant prey species that live in the open prairie.
The role of Barn Owls is diminishing because they are disappearing throughout much of their range, due to the removal of forage and nesting habitats. As barns, abandoned houses, old city buildings, and even old timber are removed, the owls lose places to nest. Even more importantly, the combination of the loss of weedy fields, pastures, and other rodent havens and the practice of "clean" agriculture, continues to diminish needed forage habitat.
Efforts to increase nesting pairs of Barn Owls through reintroduction projects have typically failed in states that have tried them. For example, nearly 400 Barn Owls released from 1979 to 1986 in Missouri produced only three known nests. These low numbers are blamed on inadequate foraging habitat. Luckily, owl habitat is still relatively abundant in Kansas. Barn Owls are not yet on the Kansas Threatened or Endangered Species lists, as they are in some states.
Some steps can be taken to help Barn Owls in local areas. Nest boxes placed in buildings within a mile of good foraging habitat are helpful. Practicing conservation tillage and maintaining wide, grassy fencerows are helpful to many kinds of wildlife, including Barn Owls. Restrained use of rat poisons is also important.
Back in my granary, the feedings began to taper off, and I checked my watch. It was now 2 a.m., time to pack up my gear and head for home. The owlets were calm for the moment, pacified with full stomachs. I opened the door and stepped into the bright, starlit night and froze when I heard a piercing scream directly overhead. Looking up, I saw a white silhouette that wheeled and screamed again, voicing its disapproval of my intrusion. Then it was gone.
It was certainly a fitting way to end the night. For an instant, I felt the chilling attention of the Barn Owl, one of nature's most specialized predators. |
Mike Blair is a staff wildlife photographer for Kansas Wildlife & Parks magazine in Pratt, Kansas, was Ducks Unlimited's featured photographer in their January/February 1991 issue.
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Building a Barn Owl nest box
By Randall P. Davis
In order to successfully attract Barn Owls to nest boxes, it is essential to select an appropriate location. The first choice is a tall barn. Boxes should be positioned high in dark corners where these reclusive birds feel safe. This placement also lessens the chance of human disturbance, as well as predation by snakes, raccoons, or cats. Make sure there are adequate openings in the building through which the owls can enter. Abandoned silos and towers also make good placements. Always use good judgment and make certain the building is structurally sound. Before installing nest boxes be sure to obtain permission from the landowner.
Man-made structures are not the only nest sites of Barn Owls. They prefer open areas, such as grassy fields and pastures, broad meadows bordered by intermittent woodlots, or even marsh edges. Near such areas, boxes can be fastened to large trees, about 15 to 20 feet off the ground. When boxes are mounted outside, they are exposed to wind, ice, and snow and should be securely fastened with ¼" x 4" lag screws. It is also helpful to prune away any limbs that might interfere with the owl's access.
Suburbanites can entice Barn Owls by erecting boxes in tall trees, under the gables of tall houses, or even in parks with suitable habitat, though you must get permission from the proper authorities before placing boxes in parks. State and private wildlife agencies also can provide information on suitable local areas.
A good time to put up a nest box is in January and February. Boxes can be utilized as roosts, however, at any time of the year. If you are fortunate enough to have Barn Owls nesting in one of your boxes, be sure to maintain it properly to insure continued use. Fall is a good time to see that the box is still solidly attached to the building or tree. Clean out all droppings, pellets, and other debris and scatter a layer of fresh pine shavings within the box.
One needn't be a master woodworker to construct a functional nest box. All it takes is a few tools and a couple of hours. To begin, gather the materials listed below.
Starting with the front piece, locate the center, then, using a compass, make a 6-inch diameter circle (it is important that the hole measure exactly six inches). Use a jigsaw to cut the hole.
Drill several ¾-inch holes (about three inches apart) in the upper one-third of each side. Drill about six 5/8-inch holes in the bottom for drainage.
Nail top to both sides, but always apply a thin line of carpenter's glue to all edges first, as the glue will reinforce all joints. Next, nail on the back and bottom. Should the nails split the plywood edge, drill 1/16-inch pilot holes ¼-inch from the edge.
Attach strap hinges to the top. Then, position front appropriately, and mark hinge holes. Remove front and drill pilot holes at marks. Replace front and screw on hinges. If screw tips protrude into nest box interior, clip them off with heavy wire cutters.
Drill pilot hole from front into edge of bottom to accept a 1-inch, No. 8, round head wood screw.
Center mounting board on back of box, and, from the interior, drill five pilot holes. Secure with five 1-inch, No. 10 screws.
Once the box is completed, all that remains is to paint it, inside and out, with a flat black paint. When the paint is dry, apply a coat of polyurethane varnish. Sound wood treatment will preserve your nest box for many nesting seasons.
Materials
From exterior grade plywood, cut:
front: 1/2" x 15" x 16"
back: 1/2" x 15" x 16"
sides (2): 1/2" x 16" x 16"
top: 1/2" x 16" x 16"
bottom: 1/2" x 15" x 15"
mounting board: 1" x 4" x 36"
No. 8, 1" round head wood screw (1)
No. 10, 1" flat head wood screws (5)
approximately 30-35 4d nails
3" strap hinges (2)
carpenter's glue
spray can flat black paint (1)
polyurethane varnish (1 pint)
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