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Thread: Pupil Shape in Black Oystercatchers

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    BPN Member Aidan Briggs's Avatar
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    Default Pupil Shape in Black Oystercatchers

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    Does anyone know the reason for this? I have seen a lot of them with misshapen, or smudged pupils. I read something about it in Birder's World a long time ago, but can't remember.

    This is a near 100% crop of an image recently posted in Avian, with an oddly shaped pupil.
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    Forum Participant John Chardine's Avatar
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    Aiden- We've had some BPN discussion before on "eye flecks" as they are called. Most oystercatchers show a fleck of some sort as do several other species. In oystercatchers, I don't think the immature birds have flecks but the older ones develop them. See these links:

    http://www.birdphotographers.net/for...ad.php?t=15001
    http://www.birdphotographers.net/for...ad.php?t=18570

    One question- is the fleck part of the pupil or just colouration on the iris? I suspect it's the latter and the work "fleck" suggests a spot of pigment. Not sure of any work that has been done on this. Will see if I can find something.

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    Eye flecks in Black Oystercatchers is sex related and generally indicates a female. This bird has pretty modest flecking as oystercatchers go so I'll refrain from going too far out on a limb.

    When this topic came up in the past I mentioned an upcoming article about this phenomonon. It has since been published and for those with a particular interest can be found here:

    Guzzetti, B.M., Talbot, S.L., Tessler, D.F., Gill, V.A., and Murphy, E.C. 2008. Secrets in the eyes of Black Oystercatchers: a new sexing technique. Journal Of Field Ornithology 79 (2): 215-223.

    I'll also take this opportunity to experiment with linking to an image. More so to troubleshoot (I've had inordinate problems with linking images) than to illuminate the issue.


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    Forum Participant John Chardine's Avatar
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    Thanks Declan. I can see the image no problem. In the bird you show, the fleck looks more like a smudge, which may be an indication of a young bird (see an image posted by Mike Milicia in the first link I give above).

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    Avian Moderator Randy Stout's Avatar
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    I think we have two separate issues here. The pupil distortion pointing towards 3:00 would be consistent with a coloboma in a human, a developmental defect in the iris often associated with underlying retinal colobomas. If the latter is present, the vision may be profoundly effected. If the vision is impaired, you would think this would be powerfully selected against genetically.

    The black pigment or smudging sounds like a sexual dimorphism, which isn't known in humans to the best of my knowledge. Pigment flakes in the iris are comment in people, and some can even have malignant potential, but I don't know the significance in birds.

    Cheers

    Randy

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    BPN Member Aidan Briggs's Avatar
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    Thanks all for the info, and John for the links.
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    Forum Participant John Chardine's Avatar
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    Quote Originally Posted by Randy Stout View Post
    I think we have two separate issues here. The pupil distortion pointing towards 3:00 would be consistent with a coloboma in a human, a developmental defect in the iris often associated with underlying retinal colobomas. If the latter is present, the vision may be profoundly effected. If the vision is impaired, you would think this would be powerfully selected against genetically.

    The black pigment or smudging sounds like a sexual dimorphism, which isn't known in humans to the best of my knowledge. Pigment flakes in the iris are comment in people, and some can even have malignant potential, but I don't know the significance in birds.

    Cheers

    Randy
    Thanks Randy. Sounds like there's some ophthalmology in your background!

    Here's a summary of what I know about this subject, which might help to focus our discussion:

    1. Eye flecks in birds occur in some species only. They occur at least in oystercatchers and pigeons and I would like to know if they occur in other species. Photographers are in a good position to find out.
    2. They are consistently found in these species so it probably does not indicate a pathology.
    3. The "flecks" are dark pigmented areas of the iris that lie adjacent to the pupil and below; they do not appear to be randomly placed.
    4. They may have a function but I'm not sure it's ever been looked at in detail.
    5. At least in oystercatchers the occurrence of flecks is sexually dimorphic with females showing them much more frequently than males. This could be the case in other "flecked" species but I'm not aware of any studies that show this.

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    Flecks are frequent and variable in many gulls. Here is a adult glaucous gull with numerous flicks rather than the clear straw eyes mentioned in field guides.


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    Forum Participant John Chardine's Avatar
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    Thanks Declan.

    Although the iris spots in oystercatchers are referred to as "flecks" I think it is somewhat misleading because they do not seem to be randomly placed on the iris like these you show in the gull. My hunch is we are dealing with something different when it comes to flecks that are immediately adjacent to the pupil, fairly large single entities, and found more frequently in certain quadrants of the iris (lower, front seems to be the trend).

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    Publisher Arthur Morris's Avatar
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    While I bring no scientific info to the table at all I can say that I have seen and photographed both NA species with weirdly shaped pupils.
    later and love, artie......... Arthur Morris/BIRDS AS ART

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