Physical Characteristics of Owls
Unlike most species of birds, male and female owls of a given species are similar in appearance. Males and females are also generally the same size in the smaller species of owls. However, this is not the case in the larger species such as the Great Horned Owl. Female Great Horned Owls are up to 25% larger than the males of the species. Some theorize this facilitates egg incubation. However, it is also possible that the females are larger so that they can protect their nests from aggressive male owls. Of course, owls vary in both size and shape from one species to another. These adaptations allow owls to hunt their preferred prey with ease and effectively cope with their environment.
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 gather light very effectively.
The cat is the only other animal that can come close to the owl's night vision capabilities. Owl eyes function in bright sunlight, too. However, it is believed that owls are not capable of seeing and interpreting a broad spectrum of colors.
Owls have extremely large eyes in proportion to the size of their heads. In some of the larger species, such as the Great Grey Owl, the eyes are larger than those of most humans. Although owl eyes are well adapted for great visual acuity, there is a drawback. Unlike the eyes of most animals, owl eyes are more flat than spherical in shape. As a result of this adaptation, owls have essentially given up the ability for eye movement. Their eyes are fixed in place by a bony structure called a sclerotic ring. As a result, they have to turn their heads to move their eyes. However, 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.
Owls have extremely sensitive ears. It is believed that some owls can hear up to 10 times better than humans can. Owls need this ability to help them find prey that they cannot see with their keen eyes. Owls can hear tiny rodents scurrying around on the ground, even under thick snow.
The unique hearing system of owls allows them to pinpoint the location of even the faintest sounds. Their ears are not lined up symmetrically like those of most animals. Having ears that are not lined up even with one another allows the owl to determine precisely from where 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 homes in on the sound.
Owl faces are shaped elliptically, like a satellite dish. This facial shape, which is very apparent in Barn Owls and Great Grey Owls, and its 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.
Feet and talons
Owls use their powerful feet and sharp talons to snare their prey. 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.
The grip strength of owls' feet is among the greatest of all raptors. Kim Long in her book Owls relates the story of a biologist who experienced this strength the hard way. The biologist was gripped by a Great Horned Owl and could not be freed from its clutches until its leg tendons were severed.
Owls are powerful fliers because their wings are relatively large in proportion to the size of their bodies and their skeletons, like those of all birds, 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, while others, like the Great Grey Owl, rarely fly more than a short distance before retreating to the sanctuary of a perch to conserve energy.
Owls, like most birds, have 2 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. Owls have far less down than most species of birds have. However, their contour feathers have special barbules that take the place of down. Their dense feathers give owls the illusion of having thick bodies, but their featherless bodies are actually surprisingly small. Their dense feathers also provide insulation, allowing owls to withstand severe cold without storing much body fat or continually eating.
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 have. Owlets will get their first adult flight feathers after they are a few months old.
Mature owls have feathers that can be considered drab colored when compared to those of other species of birds. However, the drab coloration serves to camouflage owls from predators and prey. Owls sometimes use their plumage to protect themselves from attack by condensing their feathers and closing their eyes. They can also fluff up their feathers to bluff and frighten possible attackers.