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"When the owl sings, the night is silent." Charles de Leusse

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Eurasian Eagle Owl with Hanna at Keene Schools Science Fair 2020
Eurasian Eagle Owl at Keene Schools Science Fair with Hanna Cromie. Photo by Katie Wilson

    Eurasian Eagle Owl
Class: Aves
Order: Strigiformes
Family: Strigidae

Genus: Bubo
Species: Bubo bubo

The Eurasian Eagle Owl is the largest owl in the world with two asterisks. The Great Gray Owl is on average longer, but only weighs one and a half to four pounds, while the eagle owl weighs up to ten pounds. Blackiston’s fish owl can be heavier and can possess a slightly wider wing span, with eagle owls coming in with a wing span which may exceed six feet. The eagle owl is on average about an inch and a half longer from beak to tail than Blackiston’s, and is widely distributed across Europe and all of Asia, leaving out only India and Southeast Asia, as well as France and Germany in Europe. The eagle owl has at least twelve known sub species. Blackiston’s Fish Owl is restricted to Japan, and those coastal areas of China west of Japan.

While the eagle owl is not found in the western hemisphere, it does resemble a larger, barrel chested version of the great horned owl, which pound for pound and feather for feather, may be the greatest predator that has ever lived on earth, and is found all over North America and coastal areas of Northeastern South America and over a large chunk of southern Brazil. The eagle owl and great horned owl appear to be descended out of the same genus, Bubo, which is believed to have originated out of Africa.

The deep amber eyes of the eagle owl are adapted to superior night vision. Owls are silent fliers. The leading edge of their serrated flight feathers break up the air turbulence caused by flapping wings, such that most owls approach silently, and in the dark, surprising their prey. Owls are not fast fliers, so the silence and the low light further disguise their approach.

 

The visual acuity of these nocturnal hunters is much greater than our own. As with people, the forward position of the eyes provides excellent binocular vision. The owl makes its living as a night hunter, and the need for enhanced light collection requires large pupils, whose apertures react to light sources independently of each other. In fact, their eyes are so large, that were our eyes of comparable proportion to our bodies, they’d be the size of grapefruits. The eyes are plug-shaped and are fixed snugly into the eye sockets in the skull. As a result, owls cannot swivel or "roll their eyes" as we can or look peripherally without moving their head. While humans have seven neck vertebrae, allowing us to move our heads 180 degrees, raptors have fourteen, and the owl directs its vision by rotating the head 270 degrees, through its lateral and medial axis, without moving its body, meaning they are very difficult to see when they are roosting.

 

Our eyes have about 120 million “rods” on the retina. These are for detecting motion, as well as shades of light and dark in low light. The rods are located around and outside the “fovea”, that central area of the retina where there are about 7 million color receptive “cones” clustered. An interesting experiment: stand in an area of ongoing but sporadic activity, like a meadow bordered by shrubs and saplings, an area frequented by songbirds and rodents. Note that you are more adept at picking up motion peripherally, than when the motion is in front of you, because our rods are outside the field where the cones are located. The owl’s fovea, on the other hand, is covered with rods as well as some cones, so they are much better able to detect motion in low light in any direction, than we are.

 

Like most predators, owls have a limited number of two types of color receptive cones, best at resolving light of medium wavelength (“green” area of the color spectrum) and shorter wavelength (blues). Color is less important to predators like owls, than detecting motion. Humans, whose ancestors were tree and savanna living frugivores, that is, creatures whose lives depended on locating fruit, have three types of cone, adding longer wavelength (red), for greater color resolution.

 

The eagle owl exerts a crushing power in its talons of about 700 pounds per square inch, slightly less than a wolf’s bite, allowing the owl to kill prey by crushing or puncturing the prey with its talons, or smaller prey by tearing with the beak. They can go after prey larger than what a great horned owl can take, such as small deer, foxes, dogs and cats, or birds ranging from ducks to small raptors or grouse. They also eat reptiles and amphibians as well, and the availability of prey in their habitat determines their focus.The average prey weight of a Eurasian is only marginally larger than that of a great horned owl. Any smaller mammal or bird is taken, and most prey is swallowed whole.

 

The eagle owl’s “ear tufts” are not ears at all, but feathers which aid in camouflage, and may also indicate their mood. The owl's asymmetrical ears are hidden under the dark edges of the facial disk, which is split by the beak and the forehead. Owls can hear noises ten times fainter than our hearing permits, enabling them to locate prey they cannot see, for example, prey scurrying through the snow tunnels they excavate under snowpack or prey obscured by brush.

The facial dish directs sound to the ears, and the right ear is positioned higher under the disk than the left ear, causing sounds to reach one ear a fraction of a second before it reaches the other. The owl tilts and turns its head until the sounds coordinate, and because the owl cannot change the direction of its eyes without rotating the head, the owl is at that moment, staring directly at the location of its prey.

Think about the incredible means of experiencing any environment that develops through natural selection: because the owl’s very survival depends on locating prey which is more often than not hidden, they have evolved an auditory system which allows them to pinpoint the location of prey they may not be able to see. Similarly, the wolf and bear depend on their sense of smell to locate food sources which they often can’t see, just as the snake detects prey by “tasting” the air and in the case of pit vipers, detecting heat. The bat uses a type of sonar to detect mosquitoes, and the list goes on and on. For us, our senses of hearing and smell have been blunted by living within the protective environment of civilization, and we depend primarily on our vision. When it comes to natural selection, the old saying goes “use it, or lose it”.

Courtship for eagle owls tends to start in December, but is skewed based on climate, which is related to latitude, topography and elevation. The male will find several likely nesting spots, often a raptors nest, cliff ledge with an overhang, a cave entrance or a flat area under a tree, a scrape. The male will make no special preparation, and add no material that isn’t already present, but will call to the female, which may join the male in a courtship duet, before selecting one of the spots as her nest. Eagle owls tend to be monogamous and may use the same nest every year.

The female will lay one to four eggs sequentially, about one every three days, which she alone will incubate for 30 to 36 days, while the male will hunt and deliver prey to the female. She broods the young ones for two or three weeks, feeding them prey left by the male, and cut into manageable chunks by the female. At three weeks, the owlets begin feeding themselves, and by five weeks they’re walking around, branching or sitting or perching on the edge of the nest. Fledged and flying young are cared for about six months.

Steve Hall


Eurasian Eagle Owl at Keene Schools Science Fair 20202 by Katie Wilson
Eurasian Eagle Owl at Keene Schools Science Fair with Hanna Cromie. Photo by Katie Wilson
Eurasian Eagle Owl by Deb McKenzie

Trish Marki's eagle owl at Habitat Awareness Day at the Adirondack Wildlife Refuge, Photo by Deb McKenzie

Eurasian Eagle Owl Range
Eurasian Eagle Owl Range - Wikipedia

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