Our Window on Nature

. . . exploring the world around us

Night Owls

Filed under: Birds — Lowell Christie -- May 23, 2015 @ 8:54 am

BarnOwl-LHoo, hoo-hoo, hoo, hoo. This time of year we’re audibly reminded that some birds work the night shift, for during the breeding season owls are a noisy lot. Great horned owls started their hooting clear back in January and February, and other species, like the barn owl in the picture, are migrating in now back to their warm-season homes and/or are establishing territories and nests.

All this activity requires a lot of conversation, so owl hoots, screams, and screeches fill the spring nights like the sounds of Halloween. We don’t have to see the owls to know that they are there.

Owls are raptors – birds of prey that hunt to survive. Some raptors – hawks, falcons, and eagles, for example – are diurnal, coursing through the skies and relying on keen eyesight to spot their prey. But even though most owls hunt at night (burrowing owls and short-eared owls being notable exceptions), they still possess the two basic features of raptors; feet armed with long, curved talons for locking onto their prey, and a hooked beak for tearing it into gulp-sized portions.

For the most part, owls use nests that have been built by hawks or crows, or they find ready-made holes in trees. Other times they nest on cliffside ledges or in abandoned buildings, but they never actually build their own nests. The female may make a scrape by revolving on her breast on the nest site, but that’s as far as she goes.

Because she lays her two to five eggs at two- or three-day intervals and incubates them as soon as they are laid, the female owl ends up with some hatched chicks while she’s still tending the last of the eggs. At this stage, it’s entirely up to the male to bring food for the hungry hatchlings. With a day or two head start on eating, the oldest owlet has enough of a size advantage when its nearest sibling hatches to gobble up all the food itself. Only when the eldest eats its fill will the next largest chick get dinner – and so on down the line. In times of scarcity, smaller and younger siblings may starve. This may seem harsh, but in the long run it’s beneficial to the species. Some die but at least one survives to perpetuate the family line.

Baby owls are helpless at birth. They emerge from the egg as totally inept individuals, requiring parent care, feeding, and training for a long time. More precocious bird species, such as ducks and quail, hatch full feathered and ready to find their own food almost immediately.

Owlets must stay in and around the nest for nine or 10 weeks before they’re mature enough to learn to hunt. Therein lies a problem. The nestlings grow out of the nest long before they’re strong enough to fly so they perch on branches, lunging up and down and occasionally falling out of the tree. If some well -meaning person comes upon an owlet and assumes that it’s been abandoned, he may gather up the bird and take it home. When the parents come back with dinner – no chick. The moral to the story: if you find an owlet seemingly abandoned, leave it alone. Most likely a parent will return as soon as the coast is clear.

An adult owl is beautifully adapted for hunting in the dark, as its eyes are extremely sensitive to dim light. Studies indicate that on a dark night owl eyes are roughly 35 times more light sensitive than human eyes. One scientist discovered that an owl could zero in on a mouse under light equivalent to that emitted by a candle located nearly a quarter mile away. Owls also see quite well during the day.

An owl’s eyes are much larger, proportionately, than ours; bigger even than the owl’s brain. Its eyes face forward (for acute binocular vision) and have lateral motion. Therefore, when an owl wants to see what’s behind it, it must swivel its entire head around. Old wives’ tale to the contrary, it cannot turn its head a full 360 degrees; 260 degrees is about as far as its head will spin.

The owl’s sense of hearing is as well developed as its vision. Its ears are long vertical slits located on the sides of the head. By moving flaps of skin that lie alongside the slits, the owl can scan its environment much as a dog or cat can by moving its ears. In some owl species, the right ear is located higher than the left, giving the owl an even greater ability to zero in on its prey via stereophonic sound.

Keen hearing would be of little use if an owl flapped noisily in pursuit of its prey, so owls fly silently. A row of comblike projections on the leading edge of the wing breaks the wind, and feathers covered with a soft, velvety pile help to muffle the sound. Think of how noisily a crow flies, or how a duck flaps when taking off in alarm. Yet, an owl could fly by at night without your being aware of its passage.

If a raptor is to carry off prey that weighs as much as it does, the bird must possess strong feet and a tight grip. You or I, should we suddenly sprout wings, would need to concentrate hard to carry anything as we flew. For a hawk or owl, the task is easy. Flex your hand backward at the wrist and you’ll notice how your fingers partially close. Birds of prey exhibit a similar automatic flexing of the tendon, but in their case, the talons close entirely and lock into place for as long as their legs remain flexed. Only when they reach the perch and straighten their legs does that steely grip relax, allowing them to eat their meal.

If dinner is small, the owl swallows it whole – fur, bones, and teeth are ingested along with the meat. Larger prey is torn into pieces. The indigestible parts of the meal compact into a pellet that the bird regurgitates before leaving its perch the next evening. Scientists dissecting owl pellets find mostly rodent remains, which confirms the benefits of having a resident owl.

Even though they’re seldom seen flying about, owls aren’t especially difficult to locate in the daytime. Owls usually spend the daylight hours hidden in a shaded, secluded spot where their dappled plumage blends in with the surroundings. But the owls’ eating habits indicate their presence. Since owls often use the same roost day after day, their pellets accumulate below, revealing their presence to anyone with a sharp eye on the ground.

Another way to locate an owl is to listen for other birds to spot it and attempt to chase it away. Even tiny warblers and chickadees join forces to scream at and dive-bomb an owl. The sleepy owl usually tries to ignore the commotion, but when crows or ravens mass to harass, the owl usually gives in and flies away. Either way, watch carefully and you’ll see the source of their discontent.

FMC487


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