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The Behavior of an Owl

     Most Owls are active at dusk and dawn, spending the daytime at a quiet, inconspicuous roost. They generally roost singly or in pairs, but may form flocks outside of the breeding season. (A group of Owls is called a parliament)

     An Owl's daily activity begins with preening, stretching, yawning and combing its head with its claws. The plumage is often ruffled up, and claws and toes are cleaned by nibbling with the beak. The Owl will then leave its roost, sometimes giving a call (especially in breeding season).

     Owls have a very expressive body language. Many species will bob and weave their head, as if curious about something - this is in fact to further improve their three-dimensional concept of what they are viewing.
When relaxed, the plumage is loose and fluffy. If an owl becomes alarmed, it will become slim, its feathers pulled in tightly to the body, and ear-tufts, if any, will stand straight up. A pygmy Owl will cock its tail and flick it fromm side to side when excited or alarmed. Little owls bob their body up and down when alert. When protecting young or defending itself, an Owl may assume a "threat" or defensive posture, with feathers ruffled to increase apparent size. The head may be lowered, and wings spread out and pointing down. Some species become quite aggressive when nesting, and have been known to attack humans.

     Owls will bathe in shallow water, and also in rain.

     Calls: Owls have a very wide range of vocalisations, ranging from the hoots so often associated with Owls, to whistles, screeches, screams, purrs, snorts, chitters and hisses. Hooting is often territorial, and is also associated with courting, the male usually having the lower pitched Hoot. It should be noted that not all Owl species Hoot. Owls can also make clicking noises with their tongues, often as part of a threat display. They may also clap their wings in flight as part of a mating display.

     Mobbing: Because Owls are predators, they are feared by many birds. For this reason, they are often attacked or harassed by groups of smaller birds. This is not limited to one species, as once the attack begins, many different birds will join in. Interestingly, the Owl rarely responds to the harassment, and it is just as rare for the Owl to be injured in any way! The mobbing may succeed in forcing the Owl to move on to a different area. The retreating Owl is often pursued by the mob.

     Migration: Owls are generally resident birds. Some Northern populations of certain species may escape harsh winters by moving south.

The Eye Sight of an Owl

     Of all an Owl's features, perhaps the most striking is its eyes. Large and forward facing, they may account for one to five percent of the Owl's body weight depending on species. The forward facing aspect of the eyes that give an Owl its "wise" appearance, also give it a wide range of "binocular" vision (seeing an object with both eyes at the same time). This means the owl can see objects in 3 dimensions (height, width, and depth), and can judge distances in a similar way to humans. The field of view for an owl is about 110 degrees, with about 70 degrees being binocular vision.

     By comparison, humans have a field of view that covers 180 degrees, with 140 degrees being binocular. A woodcock has an amazing 360 degree field of view, because its eyes are on the side of its head. However, less than 10 degrees of this is binocular.

     An Owl's eyes are large in order to improve their efficiency, especially under low light conditions. In fact, the eyes are so well developed, that they are not eye balls as such, but elongated tubes. They are held in place by bony structures in the skull called Sclerotic rings. For this reason, an Owl cannot "roll" or move its eyes - that is, it can only look straight ahead!
The Owl more than makes up for this by being able to turn its head around, and almost upside-down. It is able to achieve this by having a long and very flexible neck, which is not always apparent, as it is hidden by feathers and the Owl's posture. An owl's neck has 14 vertebrae, which is twice as many as humans. This allows the owl to turn its head through a range of 270 degrees measured from a forward facing position. 

     As most owls are active at night, their eyes must be very efficient at collecting and processing light. This starts with a large cornea (the transparent outer coating of the eye) and pupil (the opening at the centre of the eye). The pupil's size is controlled by the iris (the coloured membrane suspended between the cornea and lens). When the pupil is larger, more light passes through the lens and onto the large retina (light sensitive tissue on which the image is formed).
The retina of an owl's eye has an abundance of light-sensitive, rod-shaped cells appropriately called "rod" cells. Although these cells are very sensitive to light and movement, they do not react well to colour. Cells that do react to colour are called "cone" cells (shaped like a cone), and an Owl's eye possesses few of these, so most Owls see in limited colour or in monochrome.
     Since Owls have extraordinary night vision, it is often thought that they are blind in strong light. This is not true, because their pupils have a wide range of adjustment, allowing the right amount of light to strike the retina. Some species of Owls can actually see better than humans in bright light.

     To protect their eyes, Owls are equipped with 3 eyelids. They have a normal upper and lower eyelid, the upper closing when the owl blinks, and the lower closing up when the Owl is asleep. The third eyelid is called a nictitating membrane, and is a thin layer of tissue that closes diagonally across the eye, from the inside to the outside. This cleans and protects the surface of the eye.