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Have you ever seen an owl in daytime? An owl is a nocturnal bird of prey; no wonder we rarely see it during the daytime. In fact, owls come to life at night and are an apt example of nocturnal birds. Birds which can see better at night than during the day are known as nocturnal birds.
On the other hand, birds that can see better during the day than in the night are called diurnal.
About 130 species of owls are found around the world. In some countries, they are treated as auspicious birds, while in others they are regarded as symbols of wealth and wisdom. An owl has a large head and equally big eyes, short neck, broad wings and sharp claws.
What is peculiar about owls is that they can see more clearly at night than during the day and have an exceptionally good hearing power.
You must be very curious as to how nocturnal birds in general and owls in particular can see so clearly at night.
To understand this, it is essential to know how human beings see things. Light scattered by an object is focused on to the retina of our eyes by the lenses inside the eyes.
An inverted image of the object is formed on the retina, which is carried to the brain by optic nerves. The brain inverts this upside- down image, and thus we see the object as true object.
The owl’s eyes are large, forward pointing and have four special features due to which it can see more clearly at night.
Firstly, the distance between the les of its eye and the retina is more than the distance in case of the human eyes. Due to this, the image formed on the retina is bigger in size.
Secondly, the number of rods ad cones special cells which help in clarity of vision in the owl’s retina is very large---almost 10,000 per square millimeter compared to 2,000 per square millimeter in our eyes. Thus, the owl can see five times more than us.
Thirdly, its eyes have a red—colored material, chemically a protein, which makes its eyes more sensitive to light.
Fourthly, the pupils of its eyes can dilate more, thus allowing even the smallest amount of light to enter the eyes. Because of these four factors, an owl can see more clearly in darkness. Due to the extreme sensitivity of its eyes to light, objects appears too bright and uncomfortable to it in the day light. Surprisingly enough, an owl can rotate its head by 180 degrees, i.e., it can turn its head to see at what is at the back of its head.
