How can an Owl see clearly at night?

           An owl is a bird of prey with large head and eyes, short neck, broad wings and sharp claws. About 130 species of owls are found around the world. In some countries, they are treated as in auspicious birds, while in others; they are regarded as symbol of wealth and wisdom. What is peculiar about owl is that they can see more clearly at night than during the day. In fact they “come to life” at night and are an apt example of ‘nocturnal’ birds. Birds which can see more clearly at night rather than during the day are known as nocturnal birds. On the other hand, birds which have a clearer vision along the day time than during night are called ‘diurnal’.

             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 we see things. Light scattered by an object is focused on to the screen of the eyes by the lenses inside the eyes. This screen of the eyes is called the retina. An inverted image of the object is formed on the retina which is carried to the brain by optic nerves. This is erected by the brain and thus we see the object.

                 The owl’s eyes have four special features due to which it can see more clearly at night. Firstly, the distance between the lens of its eye and the retina is more than the distance in the case of human eyes. Due to this, the image formed on the retina is bigger in size. Secondly, the number of ‘rods’ and ‘cones’ (special cells which help in the vision) in the retina is very large – almost 10,000 per sq mm compared to 2,000 per sq mm in our eyes. Thus, the owl can see five times more than us. Thirdly, its eyes have a red coloured 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 into the eyes. Because of these four factors, the owl can see more clearly in darkness. Due to the extreme sensitivity of their eyes to light, objects appear too bright and uncomfortable to the eyes in the bright light of the day. Surprisingly enough, an owl can rotate its head by 180° i.e. it can see at the back of his head.