When you ask most folks, which animal is the greatest hunter in the Adirondacks, they’ll usually say “fisher” or “bobcat”, or some other charismatic predator, but I believe the great horned owl may be the most efficient predator that has ever lived on earth…. Period. Its approach to hunting is based on a combination of stealth, remarkable powers of prey detection and location, and the application of strength all out of proportion to its size. Victims of a Great Horned Owl’s silent aerial attack typically are not aware of the owl’s presence until they are within the vice-like grip of the owl's talons.
Birds do not migrate because of colder winter weather. In fact, feathers are much more effective insulators than mammalian fur, and when combined with the internal heat generated by their higher metabolism, birds are better equipped to withstand cold weather than mammals are. What drives birds to warmer climates is the lack of food available to them in the winter.
Seed eaters congregate around our feeders. Osprey and loons, whose principal diets are fish, leave to find open water. Raptors who prey on small mammals depart, because many of the animals they hunt in summer are hibernating, while many of the non-hibernators conceal their movements by constructing tunnels under the snow cover, covert paths to get from dens and nests to food sources. If you’ve ever been snowshoeing in winter, and felt yourself suddenly sink through, you stepped in one of these tunnels.
With their scent masked, and the sounds of their movements muffled by the snow, the prey of predators like bobcat, fisher, fox and coywolf may survive winter, if they have stored or can locate enough food. These predators, in turn, with their food supply diminished, become desperate and may target our pets more in winter than they would in summer.
Then there is the great horned owl. It’s not so much the size of the great horned owl. Snowy owls are bigger. A great horned owl weighs between two to four pounds, has a wing span of 36 to 60 inches, and stands from 18 inches to 2 feet tall. As with all raptor species, the female is the larger of the two sexes. What distinguishes the great horned owl is a combination of sensory abilities which will subject its prey to arguably the greatest weapon ever developed by natural selection. They don’t have to leave in winter.
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 song birds 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.
Hearing your environment
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. It’s almost not fair!
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”.
While most large birds cause noisy turbulence as the air moves over their pumping wings, the owl’s feather fluting breaks the sounds into thousands of smaller sounds not audible to the ears of mammals. In addition, while other birds preen their wings to hook the ends of their feathers together, so they can fly more efficiently, owls do not. What they lose in speed as a result, they make up in stealth, because the dissipation of the turbulence is further enhanced. As the owl drops from its perch and glides towards the sound, silent flight also enables the continuous and increasingly more accurate audible triangulation of the prey's location as the owl closes in.
The ultimate predatory weapon
If a strong athlete tries to crush your hand in a muscular grip, the crushing power in his fingers and palm is about 65 to 75 lbs. per square inch. The crushing power in a Great Horned Owl’s talons is reputed to range from 200, to an incredible 500 lbs. per square inch, ten times on average stronger than the grip of a typical human hand, so once the talons sink through the prey’s back, most prey are killed instantly. They quite literally may not know what hits them. The great horned owl is the "Jack the Ripper" of the animal kingdom, waiting in silence to deliver an overpowering attack.
Feeding on the ground is dangerous, as it may expose the owl to possible ambush. This is sometimes unavoidable, as when great horned owls kill skunks or domestic cats which may be three times their weight. Some folks ask us how it is even possible for the owl to kill such a relatively large animal. Well… consider this…. even if you feed your cat every day, it’s still a predator… it is what it is. When you let it outside, it goes hunting, picking through the ground cover, trying to flush rodents, etc. If it doesn’t look up and spot the owl, the first hint that something is wrong, may be its last thought in life, when it feels the owl’s talons penetrate its back, crushing its spine.
The owl “mantles” over the dead cat, spreading its wings as a warning to other raptors that it is guarding its prey and will fight to retain it, as it starts to tear the cat’s carcass open, so that it can fly the dismembered pieces to a safer location. What if the bobcat or fox comes out of the brush behind the owl while it is thus engaged?
Habitat and Camouflage
Great horned owls are extremely adaptive, and have the broadest range of any owl in the Americas. They are found in many different habitats, from sub-arctic tundra and prairie to mixed deciduous and coniferous forests, to mangrove swamps and rain forests, and natural selection tweaks the color of their feathers to fit in and hide in almost any habitat.
In addition, the symmetrical shape of an owl’s head, with its shorter, broader neck, assists the owl in remaining hidden from potential prey or predator. With the 270 degree neck rotation, the owl may survey its surroundings without moving its torso or legs, and with its less clearly defined profile, compared to, say, a hawk, the owl is much less likely to be noticed by other animals. I have observed well camouflaged screech owls basically disappear by simply shutting their eyes.
Territory, Courtship and Nesting
The male great horned owl defends a territory ranging in size from a square mile to about 4 square miles, with the availability of prey and the location of other great horned owl territories being the main limiting factors. Other males are forcefully excluded from their territory. They tend to be monogamous with their mates, and begin hooting back and forth in October or November.
There is something comically humorless about owls, in the sense that I've never seen an owl do anything that appeared to be playful, or fulfilling any desire for amusement. While we often see red tails chasing each other and diving as a part of courtship, owls appear stiff and serious, always businesslike. Even their courtship is almost formal, with the male bowing and presenting food, and the rubbing of beaks.
Great horned owls nest very early in the season and the female can often be seen incubating her eggs in February, covered with snow, while the male is out hunting and providing for both of them. Just as this "winged tiger" rules the night, its diurnal counterpart, the red tailed hawk, handles the day shift, preying on many of the same animals. Their territories may overlap, but great horned owls nest earlier in the winter, and since they do not build nests, but rather tend to appropriate the work of others, may take over last year's red tail nest. Great horned owls may also take over a large squirrel's nest, or use any cavity, such as in a tree, on a ledge, etc.
On occasion, these raptors may take each other's chicks, and a great horned owl may attack a red tail's nest while the hawks are roosting, but generally the two birds of prey will coexist in the same territory. If you are hiking during the late winter- early spring nesting season, and you are threatened by a great horned owl, or, for that matter, by a northern goshawk, take it to heart and turn around, or go around in a wide circle. They are warning you away from the area of their nest, and they are the only birds of prey who have on occasion actually attacked people.
Great horned owl egg clutches average two or three, laid over a number of days, which the female incubates for about 5 weeks, continuing the incubation until the hatched chicks are about two weeks old. Chicks are born sequentially, so there’s a real advantage to being the oldest, in terms of relative size, and the ability to shove aside your smaller siblings when food is offered. Chicks begin crawling out of the nest to perch on nearby branches, at 6 weeks, about a week before they start to fly. The young owls will stretch and exercise their wings.
Their initial flight may succeed, or they may flutter to the ground, and begin calling to their parents. The parents have no way to pick up the young owl, so they will feed it on the ground until it flies successfully, or a predator discovers it and ends it life.
If you’re camping, or hiking, and you discover a great horned owl chick on the ground, try to locate the nest, by looking at branches, tree hollows and ledges around you. If you find the nest, throw a sweatshirt or towel over the young owl, and gently gather it up. This should protect your from its talons. Then, climb up and return the chick to its nest. If there is another chick present, don’t be surprised if that young owl boots its sibling out of the nest… again. One way to create more food for yourself, is to kick your sibling out of the nest. If you’re uncertain what to do, call us at 855-Wolf-Man.
Why are females larger than males?
I don’t know that there’s any conclusively proven theory for this, but I suspect it has to do with the division of labor, and either way, I love to speculate, so here goes. Great horned owls have not evolved dramatically in millions of years. If we could ask Mother Nature why, she’d probably scratch her head, and say, “what exactly would we fix here? …… like requiem sharks, they’re perfect predators.”
All birds are essentially descended from theropod dinosaurs, and the earliest “birds”, for example, archaeopteryx, one of those “missing link” creatures, shared features of both. In any case, raptors certainly did evolve, from ancestors who themselves probably evolved in eco-systems where the raptors themselves had to be wary of their own predators. During the nesting season, female raptors tend to incubate the eggs, while the male is out hunting. When you’re hunting, speed and agility are more important than size, but when you’re defending the nest against attacks by larger predators, which of the females survived? The big girls did, and whenever they had female offspring, they’d pass those “big girl” genes down to their female chicks. Or, maybe not.
Digestion & other yucky stuff
Owls lack a crop, the throat pouch where other birds store food prior to digestion. Food goes down the esophagus to the proventriculus, a stomach-like organ, where enzymes, acids and mucus begin to break the food down. Next stop is the gizzard, or ventriculous, which separates out the indigestible parts, like bones, teeth and fur, which will be regurgitated later as grayish-white, sausage-shaped pellets or "castings", within about 12 to 24 hours of feeding. The act of casting signals that the bird is ready to feed again.
Like reptiles and amphibians, birds have only a single intestinal waste vent, the cloaca, from which they expunge a fecally acidic white paste and a clear urinary fluid. The reproductive organs are also concealed within the cloaca, which is why, aside from the fact that females are considerably larger, you can not tell a raptor's sex without a blood test. Owls often perch on pine branches high above and along the Wildlife Refuge trail, so look for the tell-tale castings under the trees, or the whitewash fecal spray on the trunks and branches.
Longevity and Mortality
Once they get past that first critical year, great horned owls live about 15 years in the wild. Starvation tends to be the number one killer of wild animals, and in captivity, with starvation off the table, great horned owls may live 30 to 35 years.
Adult great horned owls have no serious predators, though they may occasionally be killed by golden eagles, or northern goshawks. Foxes, bobcats, coyotes or domestic cats, may kill an owl caught out in the open while mantling over prey. The number one cause of death among young owls is starvation, while others are taken by hawks. Many owls are struck by cars, while diving at prey attracted by roadside apple cores and other food waste. Please, don’t litter, but if you throw organic waste out the car window, get it away from the road.
Great horned owls are occasionally shot by farmers, or poisoned when they eat rodenticide killed rodents. If you insist on using pesticides and rodenticides, understand that you are not only killing bugs and rodents, but the predators which eat them as well. Our use of poisons is not only ultimately self-defeating, but poisons will eventually end up in our drinking water. If you have a rodent problem inside, get a cat. Outside, build nesting boxes for barred owls, screech owls, kestrels and barn owls. They’ll control your rodents.
|Great Horned Owl chicks begin "branching" at about 6 weeks, before they can fly, grasping their way out onto branches around the nest This chick was either a "brancher" who fell, or she was kicked out of the nest by a sibling. "Poodle" was found by two campers in Keeseville. They called us in early May, and reported that the chick was hanging around their campsite. We asked them to try to find the nest, and place the chick underneath, and let Mom take care of her baby. 36 hours later, they called back, and reported that they couldn't find the nest, and that the chick was again hanging around their camp site. We retrieved the chick, and put her pet carrier in with Utah and Artemis, opening the door (left) just to feed her. After a week of this, we left the carrier door open, giving her access to the adult owls, who seemed to ignore her. Two weeks later, she had doubled her weight, and began branching near Utah. Wendy released Poodle (below) in Oct. of '09.|
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Steve & Wendy Hall
PO Box 360, 977 Springfield Road, Wilmington, NY 12997
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