September 2002

Owls

While spotting owls takes a bit more effort than other birds, it is always rewarding.

Who? A Great Horned Owl

Last winter I went out to Frederick County with Gary Dodge, a Takoma Park resident and ornithologist, to see a Snowy Owl which occasionally winters in the area. It seemed a little odd to drive all that way in hopes of finding a single bird, but I knew I would enjoy my trip out with Gary, who always seems happy to entertain the questions of a neophyte birder like myself.

Any reservation I had on the way out was cleared up when I first saw the owl sitting on a fence post in a pasture. They are truly incredible creatures, and they do seem to project a nobility and intelligence worthy of the reverence and mythological status we've given them.

It's not difficult to understand why owls have played that prominent role in the mythology of so many cultures. There are over 200 species of owls on every continent except Antarctica; they have evolved alongside us through the ages, living and hunting in a variety of habitats, from dense forest to open plains.

In traditional cultures, owls were revered as intelligent and insightful, and with their large eyes, reserved nature, and phenomenal hunting abilities, owls were often a totem for warriors. At the same time, these cultures feared the owl-they were also thought of as stealthy, nocturnal agents of sickness, death, and witchcraft.

We know owls as predators that occupy a rare niche for birds: that of nocturnal hunter. Most owls are active around dusk and dawn, but others are active at different times throughout the day and night. In most cases, owls are resident birds, meaning they do not migrate. (Some northern species will move south during the winter, although not the great distance that other birds travel.)

Owls are perfectly adapted physiologically for the nighttime hunt. The three most prominent adaptations that make them such great predators are their sharp vision, acute hearing. and a nearly silent flight. The owl's strong talons and beak are other adaptations that give it the advantage over prey.

The owl's large, forward-facing eyes provide them a 110-degree field of view, 70 degrees of which is "binocular" -it can be seen by both eyes. Binocular vision is important in hunting because it allows the owl to see its prey in three dimensions. (By comparison, humans have an impressive 180-degree field of view with 140 degrees binocular.)

Their eyes are also quite efficient at collecting and processing light. Even beyond their excellent night vision, their pupils have such a spectrum of adjustment that many owls can see better than humans in bright light.

This highly developed optic structure is held into place by bone which prevents the owl from moving its eyes in any way. The owl's neck has developed a great deal of mobility to compensate for this. The neck has 14 vertebrae-twice as many as a human-and can rotate its neck 270 degrees. (It's a rumor that they can do a full Linda Blair.)

Along with their keen eyesight, owls have a very well developed auditory system. The ears are not prominent (the ear tufts often seen on owls are more for display than hearing), but they are very acute at certain frequencies, allowing them to hear the slightest sounds of prey moving about on the ground. The owl's dish-shaped face acts as a large receiver for sound, focusing it towards the ears. Special facial muscles enable the owl to alter the "dish" and hone in on specific sounds. Even the downward-facing bill allows more sound to travel towards the ears.

One interesting adaptation in many of the mostly nocturnal owls is asymmetrical placement of the ears, so one ear is actually higher than the other. This allows the owl to pinpoint the spot where sounds are coming from. The owls also uses the time difference between when a sound reaches one ear compared to the other ear as an aid in hunting. A sound that reaches the left ear first means the prey is to the left, if an insect or bat is above the owl, the ear placed higher on the head will hear it first. It is believed that owls can detect this difference up to 30 millionths of a second.

Once the owl has located its prey it will fly towards it using a wing structure and feathers that provide near silent flight. The wings of most birds in flight act like the wing of an airplane, creating turbulence and sound as wind rushes over the wing. But the owl's wings have comb-like feathers on the front which break up the turbulence and significantly reduce noise. The silence allows the owl to continue to listen to its prey as it flies toward it and to approach without warning.

Around Takoma Park, the most common owl is the Eastern Screech Owl. It can be found in small patches of woods or in parks around the city. The Great Horned Owl and the Barred Owl are also residents, but their numbers are fewer than the Eastern Screech Owl. These brief descriptions can help you get to know our owls, and birding guides and audio tapes of owl calls can help you identify them in the field.

Eastern Screech Owl

Eastern Screech Owls inhabit a variety of habitat, including woodlands, parks, wooded suburban areas, riparian woods along streams and wetlands, orchards, and woodlands near meadows and fields. They will avoid dense forests because Great Horned Owls, which often prey on the Eastern Screech Owl, use that habitat. Eastern Screech Owls nest in cavities in large trees, and sometimes may roost behind loose boards on buildings or other structures in suburban or rural areas.

The female is slightly larger than the male, averaging a height of 9 inches and a weight of 7.5 ounces (males average 8 inches and 7 ounces.) Despite their small body size, the wingspan of the Eastern Screech Owl is 21-22 inches-over twice the length of its body.

The coloring of the Eastern Screech Owl-reddish-brown (more common in the South) or mottled grey (more common in the North)-camouflages it well as it roosts in branches close to the trunks of trees. Eastern Screech Owls also have classic bright yellow owl eyes and prominent ear tufts.

Of all the owls in North America, The Eastern Screech Owl is the most strictly nocturnal, so it is more often heard than seen. Its most common call serves as both a mating call and a territorial call. The sound is a muted trill consisting of approximately 35 notes over two to three seconds. When nesting with chicks, the owl uses a call sounding more like a horse's whinny.

Hunting is done from dusk to dawn, mostly in the first few hours of darkness. Eastern Screech Owls typically hunt while in flight, rather than from a perch. They will eat a wide range of prey, from songbirds to rats, but much of their diet consists of large insects, including beetles, roaches, cicadas, and moths.

Great Horned Owl

The Great Horned Owl has adapted to a variety of habitats, from dense forests to urban parks, and ranges throughout North America and into Central and South America.

The Great Horned Owl is a large owl, ranging from 18 to 25 inches in height and weighing 2 to 4 pounds. The wingspan of the Great Horned Owl can reach 60 inches. There are a variety of colorations, including reddish-brown, grey, and black and white. The Great Horned Owl's eyes are yellow-orange and they have very large, prominent ear tufts (the "horns").

Great Horned Owls have a variety of calls, the most common being a territorial call which is a very resonant "hoo-hoo hoooooo." This call can carry over a mile on a quiet night.

Unlike the Eastern Screech Owl, the Great Horned Owl hunts mostly from a perch on snags (dead trees) or poles, but will also glide just above the ground searching for prey. They can take prey 2 to 3 times their body weight, and while they seem to prefer rabbits and hare, at least 253 species of Great Horned Owl prey have been identified, including other owls.

The Great Horned Owl can live up to 13 years in the wild and have few natural enemies other than other Great Horned Owls, and in some instances, Northern Goshawks.

The Barred Owl

Barred Owls prefer areas with water, including swamps, riparian areas, and wet forests. Territories of the Barred Owl are quite large, ranging from 200 to 900 acres.

The Barred Owl averages 17 inches in height and can weigh up to two and a half pounds. Their wingspan ranges from 38 to 50 inches. The Barred Owl is grey-brown with distinct horizontal barring on its neck and chest and vertical barring on its lower front.

The Barred Owl calls loudly and often, in a series of hoots that is said to sound like "who cooks for you?" The call is often in a series of eight, and then it will listen for a reply. Barred Owls will sometimes call during the day as well as at night.

Barred Owls will hunt from a perch and due to their preference for wet habitat, will feed on small fish, frogs, and sometimes turtles. Smaller birds are occasionally taken from their nest, but Barred Owls have a difficult time taking other birds on the wing.

As one gets out of the city and into more rural or wooded areas, the population densities of the aforementioned owls increase, along with Barn Owls, Long-Eared Owls in rural areas, and Short-Eared Owls in pastures. In winter, Saw-Whet Owls can be found in the more rural parts of Montgomery County.

While spotting owls takes a bit more effort than other birds, it is always rewarding. It should be noted, though, that calling to owls can have a negative impact on the birds by distracting them from hunting and putting them under undue stress. As with any activity in nature, the key is to be as unintrusive as possible.

There are a number of resources which can provide information on building artificial nesting sites for owls and how to identify and call owls. Good places are The National Audubon Society (www.audubon.org), Defenders of Wildlife (www.defenders.org), and The Maryland Ornithological Society (www.mdbirds.org/index.html).