OWL ADAPTATIONS
A GREAT GRAY IN PERFECT CAMOUFLAGE © KURT LINDSAY
© CK NEALSON
SPECIES SUCCESS
An adaptation is a characteristic that helps give an animal or plant its best chance at survival in the environment where it lives. Owls live in many different environments but have evolved in order to stay at the top of the food chain.
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Below are descriptions of several important adaptations.
OWL TUFTS
Ears? Horns? No, the two bunches of feathers that look like ears are called tufts. Tufts are specialized feathers that stand up from the heads of many kinds of owls and have nothing to do with hearing.
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Owls use tufts to help camouflage, or disguise, themselves. When the tufts are raised, they resemble small twigs or branches. They help the owls stay hidden from predators. Owls hide from songbirds, too, because the little birds dive and make a racket when they spot an owl, a behavior called mobbing. The commotion warns other songbirds that an owl is in the area.
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Owls without visible tufts are called round-headed owls. Some round-headed owls raise their facial or “eyebrow” feathers to mimic tufts.
© KURT LINDSAY
THE BETTER TO HEAR YOU WITH - OWL HEARING
Where are an owls’ ears anyway? If you looked deep under the head feathers of an owl, you would discover that it has a slit on each side of its skull. Each slit is a flap of skin, called an ear conch (pronounced konk), which opens into a large ear canal, as shown above.
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An owl opens and closes its ear conches by using muscles beneath the rings of feathers around the owl’s face. The rings of feathers are called the facial disc. The facial disc captures and funnels sound into the owl’s ears, just as a TV satellite dish funnels broadcast signals into its antenna.
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Some owls have ears located directly across from each other, in symmetrical placement. Others have asymmetrical placement, where an ear on one side of the head is located above the one on the other side of the head, which increases their ability to locate sound on a vertical axis. These owls use their uneven ears to judge exactly where sound is coming from.
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If an owl hears a mouse rustling, perhaps even below a blanket of snow, the sound may reach one ear before it reaches the other ear. The owl moves its head until the noise reaches both ears at the same time. Once an owl has done this, it has pinpointed the location of the sound and is ready to pounce – even if it has not seen its prey.
© DICK WALKER
OWL EYES AND VISION
The magnificent eyes of owls come in three colors. Owl species that live in North America have bright yellow or brown eyes. Some European owls have orange eyes.
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A thin tissue, called the iris, covers the front of the eye and gives the eyeball its color. At the center of the iris is the dark, round pupil. The pupil controls how much light gets into the eye. In the bright glare of a sunny day, the pupil shrinks to block out some of the light. At night, the pupil expands to let in lots of light. An owl’s large pupils help it hunt in the dark.
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People once thought that owls were blind during the day. This is false – the Ferruginous Pygmy-Owl, for example, is one of the many owl species that hunt in broad daylight.
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Some owl species have eyes larger than humans. An owl’s eyes contain cells that are sensitive to light, just like human eyes do. Named after their shapes, these cells are called rods and cones.
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Rods help to see in dim light. Cones help to see color. An owl’s eyes are packed with rods, so they see very well in the dark. Their eyes contain very few cones, however, so what humans see in color looks mostly black and white to an owl.
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Binocular Vision
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Some birds have an eye on each side of their head, like a robin, who sees one scene with its right eye and a completely different scene with its left.
People and owls, with eyes located on the front of their face, have what is called binocular vision. What we see through one eye overlaps much of what we see through the other eye. We see an object in front of us with both eyes. Binocular vision helps owls judge how far away an object is, what size it is, and how fast it is moving.
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By moving our eyes from side to side, humans have 180 degrees field of vision, of which 120 degrees is seen by both eyes. Owls have about 125 degrees field of vision, with up to 50 degrees seen with both eyes.
© DICK WALKER
OWL EYES - NICTITATING MEMBRANES
When humans blink, our eyelids close from above, like window shades, briefly covering our eyes. An owls’ eyelids are not so simple.
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An owl does have upper lids, like us, which cover the whole eye when it blinks. The lower eyelids rise from below, covering the owl’s eyes when it is asleep.
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The third set of eyelids, called nictitating membranes, stretches from the inside corner to the outside corner of each eye. These thin, cloudy membranes close diagonally to cover the eyes and are believed to protect, moisten, and clean the owl’s eyes.
© ASHOK KHOSLA
EYES IN THE BACK OF THEIR HEAD?
Not really, although owls have the ability to look behind themselves.
While humans can look to the side just by shifting our eyes, an owl must turn its entire head to look left or right. Each enormous eyeball is locked in one position by bony plates called the sclerotic ring.
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An owl would have to turn its whole head to the right and then to left to take in normal human field of vision. Not a problem, however. Owls have 14 neck bones – double the number humans have. These neck bones, along with a special bone at the base of the skull, allow movement. An owl can turn its head 270 degrees in both directions – that is more than halfway around its body, but not quite a full turn around. This gives owls the ability to swivel their head around to see who might be sneaking up from behind.
© RADD ICENOGGLE
PHANTOM FLYERS - OWL WINGS AND FLIGHT
Owls fly skillfully without much effort, because their wings are large compared with the size and weight of their bodies. With large wings and a light body, owls can carry heavy prey animals, fly among thick vegetation and trees, and hover above open fields.
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If you were to sit outside of a moonlit night and were very quiet, you might see an owl fly past, but you probably wouldn’t hear it. Thanks to their special feathers, many owls fly almost silently.
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The outer edges of their forward wing feathers have a stiff fringe, like the teeth of a comb. The rear wing feathers have a soft, hairlike fringe. These fringed edges soften the flow of air as it moves over the wings. The fine velvety surface of the flight feathers absorbs the noise the feathers make as they slide over one another.
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The ability to fly so quietly gives the owl a big advantage. It can hear the scampering of its prey, but the prey will not likely hear the owl coming in for the capture.
FANCY FEATHERS
Many owls look bigger than they really are because they are heavily covered with feathers from top to bottom.
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In most species, female and male owls have similar feather colors and markings, but the female is usually larger than the male. Adult owls lose their feathers and grow new ones every year. But each owl stays the same color throughout its life.
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The colors of an owl’s feathers help it blend in with the natural environment and, of course, keep it warm. Snowy Owls have white feathers that help them hide in their snowy habitat. Flammulated Owls’ have dark feathers that help camouflage it when tucked up against a tree. Grassland species have light brown feathers to match the tan grasses and the brown earth.
OWL CONCEALMENT POSTURE
Feather colors are not the only things that help camouflage owls. They have other tricks to conceal themselves. Many stand tall and pull their feathers in tightly, making the owls skinnier and harder to see. When trying to conceal themselves, owls raise the whitish feathers surrounding the bill. Tufted owls also raise their tufts, and round-headed owls lift their facial and ‘eyebrow’ feathers.
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When an owl tries to hide itself by changing its shape, it is in concealment posture. In this posture, the owl’s rounded outline is broken up and is less likely to be seen.
© RADD ICENOGGLE
OWL TOES AND TALONS
Owls have four toes on each foot. Two toes point forward, one toe points backward, and the ‘reversible’ outer toe of each foot can point either forward or backward, as the owl wishes. Sometimes three of the owl’s toes point forward, sometimes only two. With two toes pointing forward and two back, known as a zygodactyl, the owl can perch securely on a branch. When the owl clutches its prey, its toes spread so the owl can get a firm grip. When the has three toes facing forward and one backward, it is known as anisodactyl.
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At the end of each toe is a long, sharp claw called a talon. The owl uses its talons to snatch, squeeze, and kill prey animals. It also uses talons to defend itself against predators, such as hawks, other owls, badgers, and raccoons.
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Many owls have feathered legs and feet for warmth. Snowy Owls, for example, who live in the cold Arctic, have heavily feathered legs and feet. Elf Owls, which live in warm, southern climates, have lightly feathered legs.
OWL PELLET PACKING
Owls swallow their food whole or in large pieces, without chewing it. An owl’s stomach doesn’t contain the digestive juices needed to break down swallowed fur, feathers, teeth, beaks, bones, insect shells, or other hard body parts. Inside the owl’s stomach, these hard pieces are packed into tight, sausage-shaped clumps called pellets. Owls usually spit up pellets onto the ground beneath their favorite roosts. Owls vomit pellets ten to twenty hours after every meal.
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Researchers study pellets to determine what each species of owl eats. Using special tools, they gently tease open the pellets and pick them apart. Sometimes they can re-create the prey animal’s skeleton with pieces of bone, like putting together a jigsaw puzzle. The skeleton may turn out to be an animal that was not known to live in the area where the owl hunted, killed, and ate it. In this way, owl pellets help scientist make important discoveries.
© DANIEL J COX / NATURAL EXPOSURES.COM
FEMALE SNOWY OWL WITH EXPOSED BROOD PATCH
OWL BROODING
Female owls will generally lay one to fourteen roundish white eggs. Females from different owl species lay different numbers of eggs. The number also depends on how much food is available. For example, if the nearby mouse populations in high, a female short-eared Owl might lay ten eggs. If the mouse population is low, she might lay just four eggs.
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Eggs are usually laid one to four days apart. The female owl sits on the eggs to keep them warm. This is called incubation. During the incubation period, the female loses the feathers on her belly in order to transfer more body heat to the eggs. She presses the warm bare skin, or brood patch, against the eggs. She lies on the nest in the incubation position, with her head low and stomach down, keeping the eggs warm all the time.
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Baby owls, called owlets or nestlings, hatch 22 to 40 days after the eggs are laid. Because eggs are laid of different days, owlets break free from their shells on different days. This is called asynchronous hatching. The first owlets to hatch can be one to two weeks older than the last ones to hatch.
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When young owls hatch, they are covered with white, downy feathers and their eyes are closed. Several days after hatching, their feathers turn gray and their eyes open. When the female sits on a nest of hatched chicks it is called brooding. For the first couple weeks of life owlets are helpless; they are unable to see, fly, or thermoregulate (maintain their own body temperature). Their mother broods them by keeping them safely under and around her in the nest.
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Male owls hunt and bring food to the nest. Female owls tear small pieces of meat off the prey animals and feed them to the nestlings. Owls grow up quickly. In just three or four weeks, the owlets start to eat prey animals whole and spit up pellets.
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Nestlings compete with each other for food. Because the older nestlings are bigger and stronger than those born a few days later, they often get most of the meat. If food is scarce, the younger owlets may even starve to death. When the owlets are two to three weeks old, both parents may leave the nest to hunt. The owlets cry out to their parents for food; these are called food begging calls.
