Begin this New Year with new hope, discoveries. I found something new to ponder.
IMAGINE my surprise when I enlarged an image in my camera to see a ragged-looking part of a Pileated Woodpecker eye. It reminded me of my torn knee meniscus. Is it the pupil or the iris? The more I magnified the image, the more I saw the yellow unevenness of the iris.
Adult males and females have yellow irises while subadults have different eye color. Certain studies suggest some adult females may have another iris color.
I searched as many adult and subadult Pileated Woodpecker images I could find on the internet along with my images. Sure enough I found similar pictures as mine with the irregular-shaped irises.
Also, I studied online images of the *Lineated Woodpecker, a really close cousin to the Pileated I saw in the Yucatan. It also sports the uneven iris.
Is this common or not in both species? Is it an “eye risk”? And why?
After researching studies about avian irises, I found little information. Some research indicated both sexes and both eyes of the Black Woodpecker of Europe have an extended dark pupil into its iris no matter where it lived. 85% of Black Woodpeckers had that mark named “Double Pupil.” BUT, with more research I found a study that looked at chicks of that species showed the dark pigment was on the iris, not the pupil.
Eye color of birds, better known as the iris, comes from pigments and light refraction. Some species can even change eye color due to handling while banding. Plus eye color can differ between sexes in some birds or at different seasons or locations. During breeding season the eye color change may derive from hormones. In other species, iris color changes as the bird becomes an adult. Examples of that include woodpeckers, loons, grebes, ducks, hawks, pheasants, gulls, auks and puffins, mimic thrushes, vireos, and blackbirds.
One theory suggests that iris pigmentation probably has little effect on vision but may serve as a signal. Perhaps it could signal mate or individual recognition or health status or the maturity of a potential mate.
Another study suggested the flecked iris of American Black Oystercatchers serve as a female trait most of the time since males lack those flecks. And European Starling females develop a yellow ring along the iris edge.
In reviewing my images, I found the iris of an immature appears to show slight aberrations in the inner circle. And one overexposed image shows a darker ring adjacent to the yellow iris. Is that part of the iris that looks like it would slough off later or is that part of the pupil that allows for expansion? You may have to enlarge the image to see that darker circle.
I even wonder if whacking rotten wood impacts the eyes.
Eye don’t know.
If any eye specialists or ornithologists know about this phenomenon, please contact me.
ENJOY NATURE’S MYSTERIES OF 2022!
*Lineated Woodpecker, Dryocopus lineatus, Carpintero Lineado (Spanish) Kolonté (Mayan)
DISCLAIMER: References do not agree or explain about this information
Kessel, B. (1951). Criteria for sexing and aging European Starlings (Sturnus vulgaris). Bird-Banding 22:16-23.
https://pubs.er.usgs.gov/publication/70031925 or Guzzetti, B. M., Talbot, S. L., Tessler, D. F., Gill, V. A., & Murphy, E. C. 2008. Secrets in the eyes of Black Oystercatchers: a new sexing technique. J. Field Orn. 79: 215–223.
Sal a Pajarear Yucatán, Birds & Reserves of the Yucatan Peninsula,The Sibley Guide to Birds
Cherie Pittillo, “nature inspired,” photographer and author, explores nature everywhere she goes. She’s identified 56 bird species in her Merida, Yucatan backyard view. Her monthly column features anecdotes about birding in Merida, Yucatan and also wildlife beyond the Yucatan.
Contact: email@example.com All rights reserved, ©Cherie Pittillo