It is just past twilight, and golden eyes scan the area. A small animal scurries below. Quick as thought and just as silently, a shadow unfurls, stoops, glides. There is just enough time for the hapless animal -- perhaps a mouse, perhaps a young, unwary rabbit -- to make one frightened sound. The eagle owl is a formidable hunter, and almost never misses.
Habitat and Identifying Traits
Eagle owls are found throughout the world, with the exceptions of Australia and the southwest Pacific Islands. They inhabit the Sahara desert, African jungles, and almost every less extreme habitat, from Sweden to Asia. They are not widely found in the UK, however, as they were once numerous there but were then hunted almost to extinction. They are thought to have existed on this planet for millions of years -- 75 million or so, in fact. They have no natural enemies, and are highly adaptable. They are also long-lived: a bird which survives its first year in the wild can expect to live about 15 to 20 years, and birds raised in captivity have lived as long as 60 years. Given those facts, then, perhaps the single most amazing thing about eagle owls is how many people have never seen one. Their elusiveness seems to be the product of two special traits: protective coloration, and near-silent flight, traits they share with most other owls.
All eagle owls, including the great horned owl, the only North American eagle owl, have a basic buff to orange coloration, streaked with brown. The mottling, on the other hand, varies according to the bird's accustomed habitat. All eagle owls are tufted, meaning they have ear tufts: feather formations atop their heads which are sometimes mistaken for ears. In actuality, the tufts are merely for display, and their position is indicative of the bird's mood. They also aid in camouflage.
Configuration and Adaptations
Their other great advantage, namely their fast and silent flight, is a product of special wing and feather configuration. Their wings are generally large compared to body size, and rounded, with a great deal of surface area. This allows for soaring flight, and cuts down on the need for flapping and excess energy expenditure. This also enables slow gliding. Many types of eagle owl, in fact, prefer to glide while hunting, scanning the area below while on the wing and then stooping quickly for prey.
All birds have up to five feather types, and eagle owls are no exceptions. The first feathers, filoplumes, actually have very little to do with flight itself. They are hairlike feathers which cover the body, are themselves covered by other feathers, and act as sensors, telling the bird how the other feathers are aligned (or misaligned, as the case may be), which aids in preening. Filoplumes are short, with just one or two barbs on the end.
The next important feather type is down. Eagle owls are covered in down while they are chicks and unable to regulate their body temperatures well, but with their fledging, they lose most of the down as their adult feathers grow in. Down's primary function is to warm the bird, and eagle owls have adapted by growing a special contour feather which has downy barbules on it, close to the skin. This effectively combines the down function into the contour feather's usual function. As the name suggests, it is contour feathers which give the bird its characteristic contours of the wings, tail, and body. Between the contour feathers and other two feather types are semiplumes. These function to fill in and support the primary flight feathers, and perhaps also to provide another layer of protection and insulation.
The primary flight feathers are contour feathers. In eagle owls, and most other owls, they are further adapted to include special barbs at the leading edges. This is the primary reason why owls can fly silently. The barbs break the flow of wind over the wing, effectively muffling the characteristic whooshing sound that they would otherwise make. Owls which prefer to hunt in the daytime often lack this special adaptation.
This raises another interesting point: owls in general, and eagle owls in specific, while largely preferring to be nocturnal, are also capable of functioning during the daytime. Their eyes are supremely adapted for making use of any available light (no animal can truly see in complete darkness, including owls), but they also include the nictitating membrane that all birds of prey have. They can stare directly into the sun without harm. Because of the adaptation which gives them their remarkable eyesight, however, owls are unable to move their eyes. To compensate for this, they are able to turn their heads, not just the 360 degrees that most birds can achieve, but up to 45 degrees beyond that on either side. Most birds sleep with their heads pillowed on their backs, beaks tucked under their wings. Owls can achieve that position and then turn past it another 45 degrees.
Mating and Nesting Habits
Eagle owls generally breed in late January or early February, unlike most birds and other creatures, which tend to produce young in the spring. The size of the clutches vary from one to four, and is very dependent upon food supply. The male is very attentive to the female, and does all the hunting for them both in most cases, for she generally will refuse to leave the clutch until the chicks have grown to a good size, sometimes even to the point of allowing herself to be picked up, although since nesting females can be very protective, that experiment is not recommended. Eagle owls, being largely nocturnal, do not build their own nests. Instead, they adopt other birds' nests, adding nothing to them. Equally as often, they clutch on the ground. This may not be as disadvantageous as it sounds, for the young grow to such a size before they can fly properly that they often simply fall from the nests, and spend the rest of their time clambering about on the ground until they can fly. This is the advantage of the early breeding: spring to summer is when the young are ready to be taught to hunt, and game is generally plentiful then, in the form of other creatures' inexperienced offspring. Faced with the demand of feeding the young, both parents will often hunt in the daytime as well during this time.
As with most other creatures in the wild, the first winter will prove the most dangerous time for the eagle owl fledglings, even with those advantages. The mortality rate for the first winter is generally high. However, those who survive to the spring will be formidable predators, and can look forward to a long lifespan with very little to threaten them.
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Sources:
"Eagle Owl." World Book Encyclopedia.
Chicago, Il: World Book, Inc., 1994.
R.D Lawrence. Owls: The Silent Flyers.
Buffalo, NY: Firefly Books, 1997.
Eagle Owl | Animal Facts | Chaffee Zoological Gardens of Fresno.
Chaffee Zoological Gardens of Fresno.
http://www.chaffeezoo.org/animals/eagleOwl.html.
15 Jan. 2004
"Eagle Owl." Encyclopædia Britannica. 2004.
Encyclopædia Britannica Premium Service.
http://www.britannica.com/eb/article?eu=32239.
15 Jan. 2004