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Owl-larming Facts!

Candace Berkeley, Product Manager
Various Carolina Staff

Updated August 2015

Introduction

Imagine being able to turn your head a full 270 degrees. Sounds impossible, right? That might be true for us, but it’s possible for an owl. For years, this range of motion and other unique physical characteristics and physiological adaptions have allowed owls to survive and even thrive in the wild. At least they have until recently, as human impact has raised the question of whether owls will one day cease to exist.


Classification

Owls belong to the phylogenetic class Aves. Two distinct families contain the more than 200 species of owls. Family Tytonidae contains approximately 17 known species of barn owls; other species belong to the family Strigidae.


Physical characteristics

Size
Unlike most species of birds, male and female owls of a given species have a similar appearance. Among small species of owls, males and females are generally the same size. However, this is not the case among larger species such as the great horned owl. Female great horned owls are up to 25% larger than their male counterparts. Some theorize this facilitates egg incubation. It is also possible that the females are larger so that they can protect their nests from aggressive male owls. Of course, variations occur in both size and shape from one owl species to another.

Sight
Owls are widely believed to have the best night vision in the animal kingdom. The eyes of most owls have large pupils and corneas that very effectively gather light. Although they are not capable of seeing and interpreting a broad spectrum of colors, owl eyes function in bright sunlight as well.



Owls have extremely large eyes in proportion to the size of their heads. For instance, the great grey owl, which is less than 3 feet tall and weighs less than 4 pounds, has eyes that are larger than those of most humans. Although owl eyes are well adapted for visual acuity, they do have a drawback. Unlike the eyes of most animals, owl eyes are flat and spherical in shape, and they are fixed in place by a bony structure called a sclerotic ring. In order to move their eyes, owls must turn their heads. Through a unique adaptation, owls can turn their heads around far enough to see directly behind them. The total range of head rotation for most owl species is an amazing 270 degrees.

Hearing
Owls have extremely sensitive ears. Scientists believe that some owls can hear up to 10 times better than humans. The unique hearing system of owls allows them to pinpoint the location of even the faintest sounds. Unlike most animals, owls’ ears are asymmetrical, an adaptation which allows them to determine the precise direction from which a sound is coming. When an owl hears something that gets its attention, it turns its head left and right and up and down until it locates the sound.

In addition to ear location, face shape also helps owls to hear. Over time, owl faces have adapted to an elliptical shape, similar to a satellite dish. This face shape, which is very apparent in barn owls and great grey owls, and the accompanying facial feathers, focus sounds directly on the owl's ears. The elliptical face and offset ears of an owl work together to form a highly sensitive and precise hearing system.

Feathers
Owls, like most birds, have two types of feathers. Contour feathers are the outer layer of feathers that provide protection from the environment and enable flight. Down is the inner layer of fluffy feathers that trap air to provide insulation from cold weather, allowing owls to withstand severe cold without storing much body fat or continually eating. Owls have far less down than most species of birds. However, their contour feathers have special barbules that take the place of down. These feathers give owls the illusion of having thick bodies, but their featherless bodies are actually surprisingly small.



Newly hatched owls do not have flight feathers. Instead, they are covered with downy feathers to keep them warm. As the owlets (owl chicks) grow, their down feathers are replaced with juvenile feathers. These feathers typically do not have the same markings as adult feathers. Owlets will get their first adult flight feathers after they are a few months old.

Mature owls have drably colored feathers in comparison to those of other species of birds. However, this drab coloration serves a purpose. It camouflages owls from potential predators and prey. By condensing their feathers and closing their eyes, owls sometimes use their plumage to protect themselves from attack. They can also fluff up their feathers to bluff and frighten possible attackers.

Flight
Owls are powerful fliers because their wings are relatively large in proportion to the size of their bodies, and their skeletons are lightweight. Their large wings are also perfectly suited to hauling heavy prey through the air. Some owls have the physical endurance to hover in the air like a hummingbird for brief periods of time to catch prey. Others, such as the great grey owl, rarely fly more than a short distance before retreating to the sanctuary of a perch to conserve energy.

Feet and talons
Owls use their powerful feet and sharp talons to snare their prey. The grip strength of owls' feet is among the greatest of all raptors. Their talons are adapted to piercing through tough animal hides and holding heavy weights without breaking. The bones in their feet are strong enough to withstand the impact made by snatching or striking prey at high speeds. Most owl species have feathers covering the top surface of their feet to protect them from the cold. The soles of their feet, which are rough and knobby to improve grip, have extra blood vessels to radiate excess heat.


Predation

Owls are quite specialized predators, having eyes and ears designed to easily locate prey and unique feathers that enable them to fly almost silently. They hunt through the night, mainly consuming rodents and other small animals. Prey is usually consumed whole, but the whole prey is not digested. An owl's digestive tract compresses the undigested portions of the prey, such as fur and bone, into a compact pellet that the owl coughs up and expels through its mouth.


Nesting

Barn owls are renowned for making nests in man-made structures, but most other species of owl seek out shelter away from the influence of people. The cavities of rotten trees, or trees hollowed out by woodpeckers, often host owl nests. Owls also readily seek out the abandoned nests of other species of birds, such as eagles, hawks, or crows. Some owl species even use the cover provided by caves and niches in rocks. Great horned owls can run squirrels out of their nest, squash it flat, and take it. Once a suitable nesting place has been found, it may be used for many years.



When owls do construct their own nests, the quality of workmanship is shoddy. Many nests are hastily constructed out of discarded owl feathers and the feathers and fur of their prey. As an exception to this, the burrowing owl chooses instead to nest in holes dug into the ground insulated with grass, plant stalks, and other material to provide protection for their young.


Courtship and reproduction

Male barn owls use a special call to attract females to their territory. The courtship often involves the male and female chasing each other in flight while both call out loudly to one another. Male barn owls also exhibit a special courtship behavior known as “moth flight.” During this ritual, the male hovers in front of a perched female to display the distinctive white areas on his chest and belly.

Another mating ritual performed by owls involves the male repeatedly flying from a female’s nest to his own to get her attention. If the female is impressed, she will respond with a unique mating call similar to that of chicks begging for food. The male responds to this call by bringing a freshly caught animal as an offering to the female. The acceptance of this offering often leads to copulation.

Some owls, such as screech owls, appear to be monogamous throughout life. However, the pair-bond relationship of other owl species may last for only one brood. Barn owls raise multiple broods in a single year if there is an abundance of prey, and they may pick different mates for each brood.

After copulation, eggs are laid individually every 1 to 2 days, but the cycle becomes erratic after the first few eggs have been laid. Several days or even weeks can separate the oldest egg from the newest.

During the incubation process, female owls rarely leave the nest except to defecate and get water. To help with incubation, female owls have a sparsely feathered brood patch on their bellies that has a higher percentage of blood vessels than other parts of the skin. Blood flow through these vessels creates a good source of heat for the eggs.



Like all birds, owls are born with an egg tooth that helps them chip away from within and break the tough eggshell. This tooth drops off a week or two after hatching. Although owls are born blind and have only a thin coat of down to protect them from cold weather, a thicker coat appears within a couple of weeks.

The parents of young owls provide them with food soon after they have hatched. Many species provide insects to their young in the early stages and whole rodents once the chicks become large enough. Spotted owls rip off the heads of their prey to make digestion and owl pellet production easier for the chicks. In some species, such as great horned owls, the parents provide larger and larger prey as the owlets increase in size.

Many young owls take their first flight, or fledge, by the time they are two months old. Once an owl begins flying, parental support ends. The parents may chase the young away or simply abandon their nests. The young are subsequently forced to feed themselves.


Mortality

Most owls in the wild live for approximately 10 years. They can live much longer, however, if conditions are favorable. Great horned owls have lived to be 19 years old, and long-eared owls have lived for as long as 27 years. Owls living in captivity as opposed to the wild can be expected to have much longer life spans. The record for longevity in captive great horned owls is 38 years, twice as long as the record for longevity in the wild!

Adult owls are near the top of the food chain and are not threatened by many animals. Large raptors, such as eagles, may attack owls if food is scarce. Likewise, large owl species may attack smaller ones on occasion.

Young adult owls are also vulnerable because they lack hunting experience. Adult owls could push them into unfamiliar hunting territory inhabited by other hostile adult owls. At least half of all young adult owls die before reaching their first birthday. The odds of survival increase greatly as they gain size and hunting experience.

Owlets are highly susceptible to disease, malnutrition, and predation by animals such as snakes, squirrels, possums, and ravens. Chicks often die directly from human interference, such as deforestation and illegal hunting. The mere presence of humans may cause the parents to abandon the nest and the young. Long-term studies have shown that the survival rate of owlets goes down as the number of humans in the area goes up.

Human encroachment on owl territories has led to the decline of owl populations in the wild. Many owl species cannot adapt to man-made changes to their ecosystems. As a result, the future of many owls, including the popular barn owl, is in danger. Pygmy owls are threatened in their southwestern United States territories due to growing towns and cities and the resulting loss of habitat. Northern spotted owls have become threatened in the United States as a result of logging in the Northwest. Loss of habitat and a low rate of successful reproduction make long-term survival questionable.


Diseases and parasites

Feather lice can torment owls and pose health problems. Owls are also susceptible to a variety of parasitic worms. Fleas and flies pester owls, but they only linger because of the decomposing materials typically found in owl nests.

Hepatosplentitis infectiosa strigum is a virus that is fatal to many owls, but some species, such as barn owls, have become immune to it. Owls are also vulnerable to pneumonia and tuberculosis. Pigeons, which some species of owls prey upon, carry a parasitic protozoan that may cause a thick deposit to form in the throats of owls. This deposit can eventually cause an owl to choke to death.


Owls in society and culture

Throughout history, owls have been linked to unnatural forces, evil, and death. Ancient Babylonians believed that the hoot of an owl at night came to represent the cries of a woman who died during childbirth. In Hungary, the owl was referred to as the bird of death. Owls were official symbols of death for ancient Egyptians. The hieroglyphic for the owl also symbolized darkness, cold, and a state of passivity.

Ancient Romans considered the sight of an owl an extremely unlucky omen. According to legend, the only way to negate the effects of this omen was to catch the owl, burn it, and then scatter its ashes in the Tiber River. It has been said that before Julius Caesar was murdered, owls were heard making their mournful cries.

However, not all societies and cultures have assigned negative attributes to owls. Buddhists have long thought the owl to be an enemy of ignorance and a representation of isolation and the need for deep meditation. In Athens, owls represented a force of mystery, but one associated with good. The owl was the symbol of the Greek goddess Athena, goddess of night, war, wisdom, and the liberal arts.

In many ancient cultures, owning or carrying a piece of an owl as a charm was thought to provide special protection from evil spirits and health problems, such as epilepsy and rabies. Other ancient cultures believed that energy, wisdom, and bravery might be imparted to the carrier of owl charms. Different cultures used different parts of owls in their charms, including the feet, feathers, eyes, heart, bones, or even the entire owl.


Conclusion

With all of their unique attributes and capabilities, owls provide fascinating insight into predator-prey dynamics, physiological adaptations, human impact, and more. Engage your students and bring important science concepts to life by studying this extraordinary bird.

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