From: jim.speirs@canrem.com (Jim Speirs) To: dannys@iis.ee.ethz.ch (Danny Schwendener) Subject: The Tiger of the Air Summary: All you ever wanted to know about the Great Horned owl, also called "tiger of the air" Article #R144. ============== The Tiger of the Air Ben Kruser The Leader, April 1988 It is 5 a.m. on a mucky March morning. I am 9 metres up a creaking dead aspen, my climbing irons tenaciously biting the bark made greasy by last night's drizzle. As I begin to peer over the edge of an abandoned crow's nest, a flash of brown streaks at me and ricochets off my safety helmet with a dull rasping sound like someone scraping a large fork against my head. A Great Horned owl, the tiger of the air, was reminding me to be gentle with her babies as I prepared to place leg bands on the owlets, now clacking wide-eyed at me from the nest's edge. Renowned for their ferocity in defence of their young and territory, Great Horned owls are marvellously built killing machines. Their unique adaptations for hunting at night are interesting to explore. To locate prey in darkness, Great Horned owls depend on their acute hearing, which enables them to detect subtle differences between sound reaching their right and left ears. Owl ears are off-set, one located higher on the head than the other. One ear opening is directed downward while the other angles upward. These physical characteristics, coupled with densely packed nerve endings in the ear, mean the Great Horned owl can quickly and accurately analyze the azimuth and elevation of a sound's source. Specialized feathers also enhance the Great Horned owl's hearing. The most adapted are those on the face. Formed into a disc, the facial ruff is an efficient sound reflector. Its densely packed feathers catch and funnel sound towards the ears, where acoustically transparent feathers allow it to filter uninterrupted into the ear canal. But how can the Great Horned owl hear the faint rustlings of its prey above the sound of its own flapping wings and the wind rushing by its face while it is in flight? Owl feathers are particularly soft and fluffy to cushion the air striking the body and make the owl's flight noiseless. These feathers extend to the feet and also serve to protect the legs from cold and animal bites. The owl's leading primary wing feathers have soft, serrated edges. As air passes over the wing, these comb-like structures further disrupt air turbulence to eliminate noise caused by air drag. The most famous of all the Great Horned owl feathers are those which give the owl its name. The "horns" or "ears" don't help hearing, but can be raised or laid back depending on the owl's state of alertness. Although the Great Horned owl depends a great deal on its hearing, its sense of sight is also well developed. It is a popular myth that owls cannot see during the day time. Their large retinas give the owl vision 50 to 100 times more powerful than that of human eyes. The Great Horned owl's good depth perception comes from binocular vision. Its eyes are fixed and cannot move in the socket. In order to see objects to the side of it, the owl must turn its head. Bird Of Prey Once the Great Horned owl's superior hearing and vision have located prey, it must catch and kill it. Its weapons are sharp claws, called talons, arming each toe. All birds have tendons that automatically pull the foot closed when the knee bends as the bird squats. This is why birds don't fall off their perches when they sleep. When an owl hits its prey feet first, the driving force of its body is transferred into its legs where the bending reflex powers the talons deep into the prey's body. The sharp, hooked beak can quickly dispatch and rip apart any food too big to swallow whole. The Great Horned owl's stomach acts like a sink trap to prevent sharp and indigestible food bits from entering and puncturing the intestines. Bone, feathers, teeth and fur are compressed into a pellet and regurgitated. If you are lucky enough to find a pellet under an owl's roost, gently pull it apart to see what the Great Horned owl had for dinner. Great Horned owls prey on many species. On the day I was banding owls, the food I found in the nests ranged from hare, grouse, pocket gopher and coot to skunks. In fact, Great Horned owls love dining on skunks occasionally, and a look at some of the interrelationships involved can help us appreciate how nature keeps balance. Owls eat skunks. Skunks prey on bees and wasps that act as a check on moths and caterpillars. Caterpillars defoliate trees and, by stripping them of leaves help weak or diseased trees die off so to make room for healthier saplings to grow. This helps maintain a diverse forest habitat, the favoured territory of Great Horned owls. But balance is very important in the chain. Too many skunks mean too few wasps and bees and large numbers of caterpillars and moths that will damage too much of the forest. Unfortunately, there are still some misguided people who consider owl "bad" because they kill for food. On a banding mission, we saw evidence of this attitude - a Great Horned owl shot and hung on a fence. A trophy? The needless destruction of owls can lead to disruption of the food chain and an imbalance leading to a less diverse and healthy forest. In the web of life where everything is connected to everything else, Great Horned owls remain a major link in the ecology of their habitat. Resources Cameron, Angus and Parnell, Peter, 1971: The Nightwatchers, Four Winds Press, New York, N.Y.; 111 pages Konishi, Masakazu, 1983: Night Owl are Good Listeners, Natural History 92(9); pp 56-59 Fergus, Chuck: The Night Hunters Owls, Wildlife Notes 175-8, Division of Information and Education, Penn. Game Comm. Knudson, Eric, 1981: The Hearing of the Barn Owl, Scientific American 245(6); pp 112-125 Welty, Carl, 1975: The Life of Birds, 2nd Edition, Saunders Co, Toronto: 623 pages Field Executive Ben Kruser, Calgary Region is a wildlife biologist.