Learning about Owls

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Introduction 

Owls are fascinating animals with an amazing ability to turn their heads a full 270 degrees. Understanding this range of motion along with other unique physical characteristics and physiological adaptations is critical to understanding how owls have been able to thrive and survive. However, the actions of humanity may mean that one day this incredible creature will cease to exist. 

Classification 

Owls are a part of the phylogenetic class Aves. With two distinct families, the Tytonidae and Strigidae, there are over 200 species of owls. 17 known species of barn owls belong to Tytonidae whilst the Strigidae family contains other known species.  

Physical characteristics 

Size

Male and female owls are very similar in appearance and size; contrary to most bird species. Among small species of owls, males and females are generally the same size. There are some exceptions, typically among larger species. One such exception is the great horned owl, whereby the male is up to 25% smaller than females of the same species. It has been theorised that this size difference is to allow for better egg incubation. Another theory suggests that the larger size of the females is to enable female owls to protect their nests from aggressive male owls. Size, shape and colour variations are very present amongst the different owl species. 

Sight 

Owls are renowned for their ability to see in the dark. They might even have the best night vision in the animal kingdom . Most owls have eyes with large pupils and corneas that allow them to gather more light. Owl’s eyes also function in bright sunlight however they are not able to see or interpreting a broad spectrum of colours. 

Proportionate to their heads, Owl’s eyes are incredibly large. Relative to human size, the great grey owl, is small at less than 3 feet tall and weighing less than 4 pounds, however their eyes are larger than our own. The disadvantage of such large eyes is that their unique flat, spherical in shape means they are fixed in place by a bony structure called a sclerotic ring. This means that owls are required to turn their heads in order to move their eyes and line of sight. To adapt, owls are able to turn their heads 270 degrees; far enough to see directly behind them. 

Hearing 

Scientists have studied Owl’s incredibly sensitive ears and estimate their hearing is almost 10 times greater than humans. Owls use a unique hearing system to pinpoint the source of a noise, regardless of how faint the sound may be. Owls’ are able to determine the precise direction of a sound due to their uniquely asymmetrical ears. When a sound captures an owl’s attention, it will move its head left, right, up and down until it is able to accurately locate the sound. The shape of an Owl’s face also contributes to its ability to hear. Owl’s have evolved an elliptical face shape, reminiscent of a satellite dish. Particularly noticeable in barn and great grey owls, this face shape and facial feathers function to focus sounds towards the owl's ears. These two features work together to operate as a highly sensitive and precise hearing system.

Feathers

Along with the majority of birds, Owls have two types of feathers; Contour and Down feathers. Contour feathers enable flight and are the outermost layer of feathers to provide a protective layer. The other layer, Down is used to describe fluffy feathers that provide an inner insulative layer that traps air; provide warmth even in severely  cold conditions. This means that owls do not need to store excess body fat or eat continually to keep warm. Compared to most birds, Owls have a limited amount of down feathers but their contour feathers have special barbules to compensate for the lack of down. Owl’s featherless bodies are surprisingly small; yet the contour feathers give the illusion of being thicker in the body.  Newly hatched owls are covered only in downy feathers to keep them warm which are then replaced with juvenile feathers as the owlets (owl chicks) grow. Juvenile feathers generally have different markings from adult feathers. After a few months, Owlets will gain their first adult flight feathers which will be drably coloured in comparison to other brightly coloured bird species. However, this more subdued colouration camouflages Owls from potential predators and prey. To protect themselves from attack, Owls will sometimes condense their feathers and close their eyes, to use their plumage as a sort of shield. To frighten possible attackers, they fluff up their feathers to bluff and appear larger. 

Flight 

With relatively large wings in proportion to the size of their bodies, and a lightweight skeleton, Owls are formidable fliers. The powerful design of their wings is a great advantage when it comes to hauling heavy prey while in flight. Some owl species are able to hover in the air or brief periods of time to catch prey; much like a hummingbird hovers to collect pollen. It is rare to see a great grey owl fly long distances as prefers to conserve energy; only flying short distances before retreating to a perch. 

Feet and talons 

Owls have powerful feet and sharp talons which they employ in the pursuit of prey. The strength of the grip of an owls’ foot rivals the greatest raptors. Owl talons are able to pierce through tough animal hides and hold heavy weights. Owls are adapted to snatching or striking prey at high speeds with bones in their feet that are strong enough to withstand the impact. To protect from the cold, the majority of owl species have evolved feathers that cover the tops of their feet; protecting them from cold temperatures and frostbite. To allow for good grip, the soles of their feet are rough and knobby and radiate excess heat due to extra blood vessels. 

Predation 

The design of Owls’ eyes and ears that allow them to locate prey easily; combined with their unique feathers that make it possible to fly almost silently, make Owls quite specialised predators. Owl’s hunt throughout the night for rodents and other small animals. Their prey is usually consumed whole, but not digested.Their digestive tract compresses undigested portions of prey, such as fur and bone, into a compact pellet for the owl to cough up through its mouth.  

Nesting 

The majority of Owl species will make shelter a substantial distance away from human populated areas. Barn owls, however, are an exception and commonly build nests in man-made structures. Common habitats for Owls include the cavities of rotten or hollowed out trees,caves and niches in rocks. Owl’s are frequently occupy other animals homes; frequently taking over abandoned nests of other large bird species. The Great horned owls even run squirrels out of their own nest, to compress it until flat, and take it with them. When a suitable nest location has been found, the owl will then use it for many years. Owls are not known for their nest building ability. When constructing their own nests, they are often hastily and poorly constructed from their own owl feathers and the feathers and fur of their prey. The burrowing owl nests in holes dug into the ground; using grass, plant stalks and other found materials to insulate the nest and protect their young.

Courtship and reproduction 

A special call is used by male owls in the hope of attracting females to their territory. Male and female Owls often chase each other mid flight; calling out loudly to each other as part of the courtship ritual. Male barn owls exhibit a unique courtship behavior, called “moth flight” wherein the male hovers before a perched female; using the opportunity to display distinctive white areas on his chest and belly. In other mating rituals, the male will repeatedly fly between the female’s nest and his own. If he has captured her interest, she will use  a mating call, reminiscent of that used by young chicks begging for food. In response, the male will bring a freshly caught animal as a meal offering. If the offering is accepted, copulation will usually commence. The pair-bond relationship can last for just one brood or in the case of some owls, such as screech owls, a monogamous life-long bond can occur. Depending on the abundance of prey, Barn Owls may create multiple broods in a year. In this case, they may choose different mates for each brood. Following copulation, Owls will lay their eggs one at a time every day or so; the cycle becoming increasingly erratic after the first couple eggs are laid. This cycle between the first and last egg laying can take several days to weeks to complete. Female owls will seldom leave their nest except to get water or defecate during the incubation process. Female owls have a brood patch on their stomach that is sparsely feathered, with an above average percentage of blood vessels that use blood flow to generate heat to aid in egg incubation. To chip away from within and break the tough eggshell, owl young are born with an egg tooth that will drop off within two weeks of hatching. Owls are born relatively helpless without their mother; they are born blind and with only a thin coat of down as protection from the cold. However, Owl parents provide them with food and shelter, and a thicker coat will grow within a couple of weeks of hatching. Some species feed their young insects to during early life and whole rodents as the chicks age. Spotted owls rip off the heads of their prey to make it easier for their chicks to digest and produce owl pellets. Great horned owls parents will provide the owlets with increasingly larger  prey as they increase in size. Within two months, most young owls will take their first flight, or fledge. Parental support finishes once an owl begins flying; some parents even chasing away or abandoning the nests of their young so they become responsible for feeding themselves. 

Mortality 

The life expectancy of most owls is roughly 10 years. There is some variation in this figure with owls living much longer in favourable conditions. In the wild, great horned owls can live to 19 years old. Long-eared owls can live up to 27 years.Owls living in captivity have much longer life expectancy. The lifespan for great horned owls in captivity is 38 years; twice as long as in the wild. Adult owls sit very high on the food chain, with few predators that prey on them. However, in times of food scarcity owls can become prey to large raptors, such as eagles. Similarly, larger owl species attack smaller owls occasionally when unable to procure another food source. Due to their lack of hunting experience, young adult owls are vulnerable to adults pushing them into unfamiliar and hostile hunting territory inhabited by other owls. Over half young adult owls never survive past their first year. An owls survival odds increase dramatically as their size and hunting experience increases. Owlets are also at greater risk of disease, malnutrition, and predation by snakes, squirrels, possums, ravens etc. Human interference also has an impact on the survival of young chicks. Deforestation and illegal hunting have negative effects on owl populations. Aside from direct action causality, human presence can cause Owl parents to abandon the nest and their young. According to long-term studies conducted on the survival rate of owls, it decreases with an increase of human numbers in the area. There has been a clear population decline in owl territories suffering from human encroachment. Due to human actions, changes in their ecosystems have left many owl species unable to adapt. The future of many owls, including the popular barn owl, is in danger. Growing towns and cities within the southwest of the United States has created a great threat to Pygmy owl survival as their habitat is decreased. Northern spotted owls are now under threat due to logging in the Northwest of the United States. Long term Owl survival is in question due to loss of habitat and a low rates of successful reproduction. 

Diseases and parasites 

Parasitic worms are not uncommon and can have many negative impacts on owl health. Fleas and flies are attracted to decomposing materials typically found within owl nests and can cause great irritation to the owl. Specifically, Feather lice can cause owls great distress and lead to further health issues. Fatal to most Owls, Hepatosplentitis infectiosa strigum is dangerous virus. Barn owls, have uniquely become immune to the virus. Owls are susceptible to pneumonia and tuberculosis. Owl food sources can also have negative health implications; Pigeons, the food source of some owls, carry a parasitic protozoan that can lead to a thick deposit to form in the throats of the owl after digesting the pigeon. The owl can eventually choke to death as a result of this deposit.

Owls in society and culture 

Owls have been associated with unnatural forces, evil, and death by many cultures throughout history. The hoot of an owl was even believed by the Ancient Babylonians to represent the cries of a woman who died during childbirth. Ancient Egyptians and Hungarians considered Owls a symbol of death.Similarly, ancient Egyptians appointed Owls as the official symbols of death. Owl hieroglyphics symbolised cold, darkness and passivity.The sight of an owl was considered a bad omen by the Ancient Romans and they believed to prevent bad luck they must catch the owl, burn the body, and then scatter its ashes in the Tiber River. When Julius Caesar was killed, it was believed that owls made mournful cries. However, some cultures associate positive attributes with Owls; Buddhists consider the Owl as a force against ignorance as well as a strong symbol of isolation and deep meditation. Owls represented a sense of positive mystery in Athens. Greek goddess Athena, goddess of night, war, wisdom, and the liberal arts was often symbolised with the Owl. Owning or carrying a piece of an owl as a charm was thought to provide special protection from evil spirits and health problems. These protection charms were commonly used to protect against epilepsy and rabies. Owl charms were believed to impart bravery, wisdom, energy in other ancient cultures. The beliefs imparted in these ancient charms varied throughout cultures and time along with the format of the protection charm; some charms were made of the feet, feathers, eyes, heart, bones, or a whole owl. 

Conclusion 

Owls allow excellent insight into predator-prey dynamics, physiological and evolutionary adaptations and the impact human populations can have on long-term Owl survival. The attributes and capabilities of owls are unique and a very engaging topic for students. Use the study of Owls to launch your student’s interest in the scientific concepts behind this extraordinary animal. 

 

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