Alvin Seng’s image of the one-eyed Buffy Fish-owl (Ketupa ketupu) was photographed at Sungei Tampines in Pasir Ris Park on 2nd July 2015. The above image shows the functioning right eye with a wide yellow iris rim and a small black pupil. These are absent in the damaged left eye. The iris regulates the size of the pupil and thus the amount of light entering the eye. During the day when it is bright, the pupil is thus small (above). At night when it is dark, the pupil is enlarged and the yellow iris is a thin rim, as seen in the image below.
As far as it can be ascertained, the one-eyed owl was first seen around the end of 2013. The damage to the eye could be the result of illegal activities by person/s unknown or it could be the result of the owl colliding against an obstacle while flying during a hunt. Whatever was the cause of the blindness, this owl is still surviving since the last sighting. Obviously it can still find food with only one eye.
Jeremiah Loei’s video clip of a pair of Buffy Fish-owls, with the one-eyed owl catching a fish confirms that the injury had not impaired its ability to hunt food.
Owls’ eyes are forward facing. Because both eyes see thing at the same time, they have binocular vision. This means that they have the ability to see the height, width and depth of objects and thus can judge distance. Of their 110 degrees range of vision, only about 70 degrees are binocular vision.
However, once an owl loses the function of one eye, this binocular vision is lost. With this loss in ability to judge distance, its ability to hunt food is only slightly diminished as it still can judge distance accurately to a certain extent. However, its ability to evade predators would be reduced – see HERE.
Alvin Seng & Jeremiah Loei