Category: Prey

WHOOOOO? IT’S OWLS – PART II

We hope you enjoyed the first half of the owl story; the head. This Treasure Hunt discusses all the rest; what goes on below the owl’s head.

Flying … Stealth is the Name of the Game

Large, soft wings give most owls the ability to fly slowly and silently. Several factors enable this advantage. Not only do owls have larger wings in comparison

to both their body mass and that of most other birds, but the wing feather is completely different from those of other birds. Instead of the usual sharp edges,
owl wing feathers are “comb-like” and break down the turbulence that normally creates the “swooshing” sound of a bird in flight. Instead the sound is muffled and the owl flies silently, enabling it to listen for tiny sounds from the movement of prey. Take a look at this short video, which is labeled “4. Owl Flight is Silent”. It shows how all the wing features of an owl combine to insure that it will arrive at its prey without a sound.

Just so you know … owls don’t get to eat when its raining. Their soft and effective feathers are not waterproof and they can’t fly when the feathers are wet.

Hunting Strategy … Time for Talons and Beak

Owls generally have a hunting territory away from their daytime roost.
As soon as a target is located, the owl will fly towards it, keeping its head in line with the target until the last moment. This is when the owl pulls its head back, and thrusts its feet forward with its talons spread. However, owls have an unusual adaptation that involves their feet. Like other raptors, owls typically have three talons pointing forward and one pointing backward. But owls can rotate one of their forward-pointing toes to the back, making their toe arrangement more like that of a woodpecker, and becomes, yet another body part that is able to swivel! The advantage of this talon talent is evident when the owl grasps its food. If a rabbit or mouse is struggling to get away, it’s very helpful to have an equal number of talons on each side to ensure the prey won’t free itself. Exhibiting truly exceptional grip, owls also have the ability to lock their toes around an object so that they don’t need to continually contract their muscles. This gives them maximum grip with minimal effort!

The force of the impact of the talons is usually enough to stun the prey, which is then dispatched with a snap of the beak. Once caught, smaller prey is taken away in the beak, or eaten immediately. Larger prey is carried off in the talons.

Food … Finally We Get to Eat!

Owls are carnivores, but their main food largely depends on the species of owl. For example, in the case of More Mesa’s owls, the Great Horned Owl eats larger mammals like rabbits, squirrels, raccoons, big birds and skunks! (It’s OK … owls can’t smell!) Long-eared, Short-eared and Barn Owls eat smaller mammals, like voles, mice and rats. The smallest owls, Western Screech and Burrowing eat insects, small birds and sometimes small mammals. Here comes the test to see if you were paying attention in Part I of owls! All our owls have yellow eyes except the Barn Owl that has black eyes. Who hunts when?

Digestion … It’s Not That Easy

Like other birds, owls cannot chew their food – small prey items are swallowed whole, while larger prey are torn into smaller pieces before being swallowed. For example, Barn Owls swallow their prey whole, skin, bones, and all … and they eat up to 1,000 mice each year.
Rather than being stored for later, the owl’s dinner is passed directly to the digestive system. Owl stomachs have two parts, one that does the chemistry necessary for digestion and the other (the gizzard) is what holds, and eventually compresses the trash (fur, teeth, bones, feathers etc.) The digestible part is allowed to pass through the system with useful components being absorbed into the body and the waste of food digestion being excreted at the end of the digestive tract … the “white stuff” that birds leave everywhere.
Several hours after eating, indigestible parts (trash that is still in the gizzard) are compressed into a pellet that ends up, after several meals, being the same shape as the gizzard. (Think of the gizzard as a trash compactor and you get the idea.) The pellet then travels

back up from the gizzard to the “chemistry section” and remains there for up to 10 hours before being regurgitated. Because the stored pellet partially blocks the owl’s digestive system, new prey cannot be swallowed until the pellet is ejected. Regurgitation looks really painful, but at least the owl can eat again.

The Cycle of Life

Most owls reach sexual maturity and are ready to reproduce in about a year. The decision to reproduce is not always at a specific time of year, but often based on available food supplies. Also, various species begin courtship at surprising times of the year. For example, the Great Horned Owl begins in December; even in very cold places! As might be expected, and after we have explored their lifeway in such depth, courtship among owls is mostly about sound. Depending on the species, various specialized hooting is used for attracting mates, as well as nodding and bowing and appropriately enough … billing and cooing.

Although variations exist for different species, owls are usually monogamous, or pair with the same mate for several seasons. They don’t construct nests as such, instead they are opportunistic nesters, using ready-made sites or taking over the abandoned nests of other birds. They also use holes in trees, barns or other buildings. And when you provide these birds with an owl box, they think they have died and gone to heaven! However, Burrowing Owls nest underground; appropriately enough, in abandoned burrows.

Depending on the species, the nest will mostly house a few eggs. During incubation, eggs are rarely left alone. The female, who is always larger than the male, will incubate the eggs. She develops a brood patch, which is a sparsely feathered part on the belly, with a higher density of blood vessels than other parts of the skin. This allows eggs to receive warmth directly from her through this area, and they will hatch in about 30 days. Owl chicks, similar to the Western Gull chicks we talked about in a previous Treasure Hunt, hatch with the aid of an “egg tooth.”

Dad delivers food to the nest up to 10 times a day. Prey is ripped apart by the adults until such time that the chicks can swallow it whole. At that time the chicks also begin producing pellets. They fledge anywhere from 4 to 10 weeks, depending on the species. Parents care for the fledglings an additional few weeks to few months, and then the circle is complete again.

Mythology

Throughout history and across many cultures, people have regarded owls with both fascination and awe. In ancient times owls represented wisdom and helpfulness. However, by the Middle Ages in Europe, the owl became an associate of witches and the inhabitant of dark, lonely and evil places. In the eighteenth century, science eliminated some of the mystery about owls, and now with superstitions dying out in many parts of the world, the owl has returned to its position as a symbol of wisdom.

Finally, and you knew this was coming, we have to talk about the major role played by owls in the Harry Potter tales. Since Harry’s world does not have a federal postal service, owls carry all the mail … messy … but they get the job done! And, in addition to mail service, Harry’s owl Hedwig, provides warm companionship whenever he is blue and lonely. (FYI: Hedwig is a Snowy Owl and native to Arctic like regions!)

We are indebted to owlpages.com for providing its very professional and accurate information on owls, as well as several of our most interesting photos.

Remember: Six Feet Apart and Stay Safe,

Valerie

WHOOOOO? … IT’S OWLS

Many members of this treasure’s family live on More Mesa. However, they may be more difficult to see, although easier to hear … especially if you are willing to venture out onto More Mesa at night. The last Christmas Bird Count recorded a phenomenal six separate species of owls on More Mesa. Over the many decades we have been collecting sightings data, these are the most owl species ever recorded, at one time, and there are some species we have rarely, if ever seen!

The largest of our hooting avians is the Great-horned Owl at 23 inches. Significantly smaller are the Barn, Short-eared and Long-eared Owls, all of which are between 13 and 16 inches. Our tiniest owls are the Burrowing and the Western Screech Owls, about 10 inches

Although we think of owls as hunting only at night, that is not the case. (More about this when we look at owl sight.) You can quickly determine the hunting habits of an owl by the color of its eyes; black or brown hunt at night, yellow hunt at dawn and dusk and orange hunt in the daytime. However, a majority of the owl family are nocturnal creatures and do most of their hunting when light levels are low. Why? Because many owls hunt for rodents, and rodents are active at night. The next obvious question is, “How does an owl hunt in the dark?” The answer is that its head, and all the elements of the head have evolved precisely for this very purpose; that is, hunting in the dark. Specifically, owls have incredible sight, a neck that can rotate its head a full 270 degrees and amazing hearing.

HEADS UP! … PART I

This treasure hunt proved to be so fascinating and interesting that the tale could not be told in a single issue. So, the story of the Owl will come in two parts; first we will describe all the functions that are carried out in the head and the next issue will conclude the tale with details of what happens in the rest of the owl’s body.

Incredible Sight … At Night

Owls have extremely large eyes, in a very small skull. The eye is tubular in shape, accounts for up to 5% of the owl’s weight and is held in place with bones. It’s definitely nothing like our eyes, that are round, weigh .0003% of our body weight and are held in place with muscles. Light collection is also aided by a reflective surface behind the retina which reflects the image back after it has passed through the eye. This gives the owl a chance to collect twice the light for discerning the image. That information is then passed on to the brain.

We discussed rods and cones of bee eyesight in an earlier Hunt. Cones are important to bees since they have a great need to see colors. For owls, it’s all about rods! Faced with low light levels, you need lots and lots of rods. Indeed, owls have 5 times as many rods as humans, one million rods per square millimeter! As a result, they can see 35-100 times better than we can at night. For example, Barn Owls can see a mouse at 6-7 feet with an illumination the equivalent of the light of a match a mile away.

The downside of owl vision is that they are very farsighted, and cannot focus well on objects that are within a couple of inches. So, to compensate, Mother Nature has equipped them with whisker-like tiny feathers (filoplumes) around their beaks and feet to help them detect objects close in, as well as “feel out” the food they have captured.
Another factor on the “upside” is that most bird eyes are usually at their sides, but owl eyes face forward, as do ours. This means owls also have binocular vision, similar to ours, and it gives them increased depth perception … even in the dark. A final feature of owl eyes is that the iris of the eye can adjust so owls can see in the daytime, unlike other nocturnal animals that can only see at night.
And to wrap up, these, oh so important, owl eyes are well protected with three eyelids. The upper eyelid closes down when the owl blinks and the lower closes up for sleep. The third is a translucent membrane that moves horizontally from the inner corner of the eye to the outer. Its task is to view prey, while keeping the eye safe during the last part of the capture.

---

The Swivel … Takes it All In

With its huge eyeball, held in place with bones, an owl cannot roll its eyes to look around. Instead, when pinpointing prey, it moves its entire head, an incredible 270 degrees in either direction and 90 degrees up and down. How can it achieve these feats? First, owls have twice the number of vertebrae in their necks as other birds. And second, they have a blood pooling system that collects blood to power their brains when neck movement cuts off circulation.

Hearing … Sophisticated Sonar

When they cannot see their prey, Owls rely on hearing. A hunting owl, therefore, will use the calls and movements made by a mouse, vole or shrew to direct its strike. These sounds are channeled in many owls by a very pronounced facial disc, which acts like a “radar dish”, trapping and focusing the sounds into the ear openings. Even the owl beak is designed pointed downward to maximize sound collection.

Owl ears are hidden inside feathers and they are higher on one side than the other. This positioning allows the owl to pinpoint and position its prey by turning its head until the sound reaches both ears at the same time. The accuracy of this sound/brain interaction is such that owls can detect a left/right time difference of about 30 millionths of a second! To see owl hearing in action, check out this video of a Great Gray Owl. This species lives in evergreen forests in the far north and on high mountains. In these environments, prey is very often beneath the snow, even in summer. As a result, the Great Gray is virtually blind when it hunts. It seems “flying blind” isn’t a problem when the rest of your face is configured to listen.

Be on the lookout for Part II of the Owl Story that will discuss flight, hunting, food, digestion, reproduction and owls in mythology. More fun to come!

We are indebted to owlpages.com for providing very professional and accurate information on owls.

Remember: Six Feet Apart and Stay Safe,

Valerie