“Some Red-breasted Parakeets (Psittacula alexandri) were harvesting fruits from a few oil palm trees and one of the pictures taken is particularly interesting.
“In the picture on the left, three birds are shown. Do you notice anything unusual? Look at the eye of the bird in the middle – [see the enlarged image below-left]. The sclera, the white part of the eye, is very prominent in this bird. The iris or pupil is obviously constricted. There is also a black line across the sclera starting from the iris towards the beak.
“From what I know, the pupil in human eye varies in size to calibrate the amount of light reaching the retina. Not sure how this work in birds. In a picture taken 11 seconds later, the iris or pupil returned to normal – [see the enlarged image below-right].
“There is a lack of clarity and detail in the iris and pupil even in the blown-up images due to insufficient lighting condition. Curious to see more of the parakeet’s eye details, I searched through my hard disk and managed to find two images of another Red-Breasted Parakeet, which were taken seconds apart and with the bird in good light (below). The images are for comparison. If you look closely, you can see the iris and pupil distinctly. Comparison of both iris and pupil show that the sizes of both are slightly different. Does this mean that both iris and pupil are capable of size control?
“Would appreciate anyone who can shed some light on this.”
Kwong Wai Chong
8th October 2010