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Owl

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Owl
Ural owl.jpg
Scientific Classification
Families

Owls are any of the species of birds that make up the order Strigiformes. Out of the 6 genera that make up the order, there are only 2 that are still in existence, Strigidae and Tytonidae, the rest are fossilized. [1] Most owls are found to be nocturnal. They are very precise birds of prey when hunting. They range greatly in size and feather colors and designs. [2]

Body Design

Immensely long wingspan

From the wide range of species, owls vary in size and strength greatly. From the smallest pygmy owl at 4.5" to the largest Eurasian eagle owl being 28" tall. Although male and females don't differentiate in appearance very much, females tend to be about 25% larger than most males of the same species. They also have a long flexible neck that enables the owl to turn its head around and even upside down. They have this long neck because they have 14 vertebrae, which is twice as many as humans have. This gives them the ability to rotate their heads 270 degrees. [3]

The owls' most famous physical feature is their astonishingly large eyes. They are so large that they account for 1-5% of the owl's total body weight. They have 3 dimensional vision, which enables them to measure height, width, and depth and the ability to measure distance - such like that of humans. The wide range of pupil adjustments allow them to better direct their vision, providing better efficiency. Looking straight ahead, they have a 110 degree field of vision. 70 of the 110 degrees is binocular vision, leaving 20 degrees of left and 20 degrees of right monocular vision. They have great visual efficiency, not only in light but especially when they are under low light conditions. Unlike most other animals, owls have 3 eyelids. They have an upper lid that closes when it blinks, a lower lid that closes upward when it is sleeping, and a nictitating membrane (thin layer of tissue that closes diagonally across the eye)that cleans and protects the surface of the eye. Their eyes are not eye "balls" like most other mammals, but are elongated tubes that are held by bony structures in the skull. Because they aren't balls, owls are only able to look straight ahead and can't roll their eyes. [4]

Like their vision, owls have a highly developed auditory system. It is partially due to their medulla in the brain is much more complex than other birds, it contains more than 95,000 neurons. Their ears are located on the sides of their head, behind their eyes. The ear openings themselves vary in shape according to different species. Some have a round aperture while others have an oblong slit. These openings are covered by a valve called an operculum. In some species, they have asymmetrically set ear openings. They also have a pronounced facial disc which acts like a radar disc and guides sounds to the ear openings. Sounds can be better guided by altering the facial disc through muscles in the face. They can hear very acute sounds at certain frequencies. Sounds are also detected by the minute time difference between the left and right ears. When a sound is detected by say the left ear, the owl will turn its head so that the right ear is in the same spot as the left ear previously was. This way it can determine the location of its prey by how long it takes the sound to reach the right ear after hitting the left. [5]

Reproduction

4 week old Ethiopian Eagle owl is covered in a coat of natal down feathers

Breeding comes at all different times according to the specific owl species. Most owls, usually those that live in temperate or sub-arctic regions often breed during spring. It changes when owls want to breed in a certain weather condition, food abundance, competition from other owls, diseases, and when or if they can find a suitable mate. When mates are available the couples often go through courtship rituals that involve calling. A female is attracted to a male by his good nest site, his flights, calls, and food offerings. Different owl couples have relationships that last from one breeding season, to a year, or a lifetime. During mating and breeding season owls will become very territorial. They will violently attack any intruder with their talons and feet directed at the on-comers face and eyes. As a warning to intruders, some will show buoyant flight and wing clapping displays. [6]

For most owls the number of eggs is approximately 3-4 in a nest. Depending on the species and the time of season, eggs could possibly vary from 1-13 eggs at a time. The eggs are incubated for 30 days after they have hatched and are rarely left alone during this time. The females incubate the eggs by a special feature they have on their bellies. They have a brood patch which is a sparsely feathered area that contains a high density of blood vessels. This gives the eggs a warm source when the mother comes in contact with them. [7]

A chick hatches from the egg after incubation with the help of a tooth, or protrusion on the beak. One to two weeks later they will make their drop offs-leave the nest. Since the eggs are laid over a period of several days and not all at once, the hatching of the eggs will also be during different times. The staggering of the hatches will give the first few chicks an advantage because they will have more time to develop and strengthen. By the time the rest of the chicks hatch they will be larger, stronger, and more active. It is rare to find all the chicks survive, only unless there is a bountiful supply of food. Thus, most of the time, the youngest, which are normally the weakest, will starve or be killed by an older sibling. Though this process seems harsh, it will better ensure that some of the owls will survive and reproduce in their lifetime. If all of were to be given a small portion of food it is most likely that all would die. [8]

Ecology

These owls live in various places around the world in several different types of environments. Depending on the owl species they could live from thick forests to open prairies. They are present on every continent with the exception of Antarctica. [9]

These specific aviaries tend to shy away from constructing their own nests. They would prefer to use old ones made and abandoned by other birds or make due with other sites that lay available. Nest sites vary greatly between owls. For example, some will use holes in trees or tussocks of grass like the short eared and long eared owls. Those that live and breed in the open terrain will find a nest on the ground. On the other hand, those that live in the arctic tundra will use a hollow in the ground. Others will prefer holes in barns and buildings or cracks in rock ledges. They will continue to use their territories in years to come as long as they are able to. These nests are mostly well concealed and will provide stable protection for them. [10]

They feed off of a wide selection including invertebrates-such as insects-, fish, reptiles, amphibians, birds, and small animals. Food varies depending on a specific species. In order to catch prey most owls sit on a perch and wait until they locate a prey before they swoop in for the kill. Others fly around until they locate a prey and then dive straight for it and then they thrust their feet forward, talons spread apart with two talons backward and two talons forward. When they have to hold large prey and fly they hold a certain posture called mantling. This is a way to shield its prey with their wings from other predators. When there is extra food they store it in a cache or their nest. After digestion, the undigested pieces of food are regurgitated through pellets. These pellets begin to appear when a chick first begins eating. [11]

Owl pellets are popular school dissection labs.

Pellets

Owl pellets are created inside of the owls stomach and are filled with all sorts of prey's anatomy. It takes several hours for these pellets to develop inside the animal after the food has been taken in. They are composed of several indigestible animal parts such as fur, bones, teeth, and feathers. All of this is made in the gizzard of the stomach. Everything the owl takes in at one time and can't be digested will be made into one, single pellet. Pellets are created as a way to rid the owl of indigestible wastes. They come back up the digestive tract and into the first section of the stomach called the proventriculus. The pellet will remain there for around 10 hours. The owl can't eat once the pellets have been formed because they block the digestive system. They must wait until it is fully regurgitated to begin eating again. When the pellets are finally ready to come out the owl will not fly. They will close their eyes, stretch their neck up and out, open their beaks, and the pellet will just drop out. These pellets are picked up and examined by many people because they contain so many interesting scraps like bones and teeth. [12]

Gallery

References