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 Great Horned Owl

Bubo virginianus

Introduction

Owls are considered intelligent, mysterious, intriguing and even spooky.

From the time we begin to read we are presented with “wise” owl characters:

the owl in “The Owl and the Pussycat", Wol in “Winnie the Pooh”,

Archimedes in “The Sword and the Stone“ and Hedwig, Harry Potter’s

best friend in “The Philosopher’s Stone” to mention a few.

 

The idea that owls are intelligent is very pervasive…..for example - what do we call a group of owls?… a flock? a flight? a gaggle?…no, most commonly owls are referred to as a “wisdom” of owls or a  ‘parliament’ of owls.

 

Their exceptional eyesight and hearing support the conception that owls are “wise”. Formidable hunters even in low light, their sensory acuities suggest that owls see and hear what others don’t and thus are symbols of insight and perception. 

 

This web page focuses on the most common owl of BC and the Sunshine Coast, the Great Horned Owl, (GHO) and is intended to increase our understanding and appreciation of this amazing raptor.

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Range

The Great Horned Owl is one of the most common owls in North America, equally at home in deserts, wetlands, forests, grasslands, backyards, and cities. This bird does not find it necessary to make seasonal migrations. Banded owls that were later recovered had moved less than 80 km from where they were born. GHOs are most likely to establish a year round residence with a hunting range of 8 to 10 square kilometres. Quoting from Hinterland Who’s Who, “Such adaptation by a species is truly remarkable and has few parallels in ornithology.” In other words, it is hard to find a bird that can adapt better than the GHO.

Characteristics

Widely spaced  on the owl’s head are the feathery tufts that have given it the name “great horned”. It must be noted that these tufts of feathers are called plumicorns, and are neither horns nor ears

 

Size:

According to birdwatchinghq.com these are the size statistics for the Great Horned Owl.

Length: 17-25 inches (43 – 64 cm)

Weight: 2.5 to 4 pounds (1134 – 1814 grams)

Wingspan: 3 – 5 feet (91-153 cm)

Differences between the male and female:

How do you distinguish between the male and the female? As with almost all raptors, the female is larger and heavier than the male. When they hoot, her hoot is pitched slightly higher than the male’s creating that wonderful duet that you might hear some evening. A comprehensive site for listening to the hoots, chitter, squawks, hisses and bill clacking is available at:

https://www.internationalowlcenter.org/ghovocalizations.html?gad_source=1&gclid=Cj0KCQiAv8SsBhC7ARIsALIkVT2TO_xzvbVoooSt-i53UH4WFOMb93MVcWyAaFYeYCtOANOnLUSUOgQaArKUEALw_wcB.

Colouration:

The Great Horned Owl (GHO) has a facial disk that varies in colour from a light orange-buff to brownish-gray and dark brown. Distinctive to this species are the very large yellow eyes and the bright white patch at the throat that expands during vocalization. The plumage is heavily barred with black on the buff or white underparts, while the upper parts are a dark grayish brown mottled with grey, brown and black. We may complain that we don’t see many GHOs but this is frequently because, as they sit quietly in a tree, their colouration camouflages them so successfully.

Feet:

One of the most interesting descriptions of this owl’s feet comes from birdnote.org -“The grip strength in those feet — 200 to 500 pounds per square inch—is equal to that of the much larger Bald Eagle and up to six times stronger than the handshake of a bodybuilder. Talk about a “death grip!

 

The feet of the GHO have feathers that are touch sensitive. As it swoops in on a prey the GHO knows immediately whether the attack has been successful or whether it has merely twigs and leaves in its grasp. The four toes are adapted so that the outermost toes rotates forward and backwards giving it an advantage when clutching prey (or sitting on a branch). Almost all prey are killed by being crushed by the owl's feet and possibly stabbed by its talons. The GHO is one of a very few birds that has talons longer than some bear claws.

Wings:

Great Horned Owls have unique wing and feather features that enable them to be very stealthy predators; the kind of predator that relies more on surprise than speed. Wing feathers have comb-like serrations on the leading edge and a wispy fringe on the trailing edge. In flight, this allows the air to slip through the feathers and makes the GHO one of the few birds that can flap its wings without producing a “swooshing” sound. They have large wings relative to their body mass, which let them fly unusually slowly. At night…. gliding noiselessly…. slowly…. with little flapping—you can imagine how the prey doesn’t get any warning and doesn’t know to run before it’s too late. In the following video you can’t help feeling sorry for the mouse.

Eyesight:

There are many extraordinary things to say about this owl’s eyes, but foremost is simply how enormous they are. The GHO’s eyes make up as much as 5 percent of  this birds' total body weight. That may not sound like a lot, but in comparison, our eyeballs are about 0.0003 percent of our total weight. Humans would have to have eyes as big as softballs to be of comparable size. 

 

The owl’s eyes are held in place by a bony structure called a sclerotic ring. Due to the size of the eyes, there is no room left for the muscles that would control eye position and movement. This results in the piercing “stare” as the owl is only able to look straight ahead. To have a wider field of vision, the owl must turn its whole head. Fortunately, the vertebrae and arteries in the owl’s neck are adapted to allow the head to swivel 270 degrees.

These enormous eyes have pupils that open widely to take advantage of low light. The GHO’s eyes are actually not round, but cylindrical in shape which creates more distance from the lens to the retina. Compared to round eyes, the GHO’s eyes function more like a telephoto lens allowing  clearer sight at a greater distance. They have more rods than cones which means they have poor colour vision and excellent night vision. As well, they have a translucent “third eyelid” that closes horizontally from the inside corner of the GHO’s eye. These nictitating membranes protect their eyes from dust and debris when in flight.

Hearing:

The ears of the Great Horned owl are actually just simple holes in the bird’s head on either side of the face. These “holes” are hidden under the curved lines of the dark feathers that form the facial disc. The GHO can actually raise these short facial disk feathers to amplify sound, similar to you cupping your hands behind your ears. The Great Horned Owl’s hearing is so acute that even at a considerable distance it can discern small prey moving under leaves and snow. What is even more interesting is that their ears are actually offset with the right ear being a little higher than the left. This allows the owl to be able to triangulate sound. It tilts its head until the sound is equal in both ears and at this point, the owl knows it has its prey in its sight line.

Sense of smell:

Interestingly, a Great Horned Owls’ sense of smell is so weak that they even attack and eat skunks!

 

Diet and Digestion:

The GHO, in keeping with its reputation for being adaptive,  is described as not being “picky” about what it eats. Although it prefers mammals such as rats, mice, voles, rabbits and ground squirrels, it will eat birds up to the size of geese, ducks, hawks and small owls. Snakes, lizards, frogs, insects and even occasionally fish can become part of its very diverse diet. 

Owls usually consume smaller prey whole. They have a have a two-part digestive system. The first part of this digestive system breaks down the soft tissues and then sends the fur, bones and other remains to the gizzard. In the gizzard what can’t be used undergoes a kind of trash compactor action that produces a pellet.

The owl will not be able to eat again until it gets rid of the pellet. Ten to twelve hours after a meal, when the owl is hungry again, its esophagus will spasm and the pellet will be ejected from the gizzard.

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