The eyes of the Red-breasted Parakeet

posted in: Morphology-Develop., Parrots | 7

“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
Singapore
8th October 2010

7 Responses

  1. Tammy hartnett

    This is a common occurence in (captive)Psittacines. I have witnessed many psittacines with this pupal dilation. I believe it’s due to excited nature…. intruder?(how close were you and for how long? or breeding season-defending the nesting territory. Hope this helps. Tammy

  2. Hey,

    I’ve used to keep these parakeets as pets before and they are capable of dilating the pupil whenever they’re excited or angry. They will try to puffen up their feathers when angry.

  3. Thanks for responding.. I was about 8 metres from the birds. The birds did not look alarmed and were still feeding on the fruits.

    I am still intrigued. Did not jnow that the iris is capable of changing in size. Have always thought that only the pupil change its size in response to light.

    • Any idea what is the black line across the sclera? I don’t think it is a foreign object.

    • Sun Chong Hong

      The iris is like the diaphragm, and the pupil is like the aperture of a camera lens. When the diaphragm enlarges, the aperture gets smaller, and vice versa. Besides responding to the light, the human pupil size also changes according to emotions. Now I know birds, at least in parakeets, the same thing is true.

  4. Birds have voluntary control of the sphincter muscles in their pupils, and can constrict and dilate them at will. The iris is not changing size, it is an optical illusion created by the difference in pupil size.

    • Sun Chong Hong

      In layman’s language, the pupil is a hole. You can’t have anything in a hole. The muscles are in the iris. The actions of the muscles in the iris result in changes in pupil sizes.

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