Oystercatcher Eyes

[Axel Hildebrandt]

Does someone know why oystercatcher eyes have this strong shadow under the pupil? My guess is that the pupil stands out more than in other birds and causes this shadow if the sun is not very low. I've never noticed this in other bird's eyes. Any ideas?

[Juan Aragonés]

Axel, some researchers are trying to stablish a relationship between the black spot on the eye and the sex, (please have a look on this paper http://www3.interscience.wiley.com/journal/120088545/abstract?CRETRY=1&SRETRY=0) but I am not sure about it . It doesn´t seems a very clear relationship between sex and the eye black spot. Maybe there are more factors working on this trait like, i.e, age. One thing is for sure, I have seen one of those birds very close to me and is not the shadow of the pupil but a dark spot.
Interesting question and fantastic image BTW:)

[Lana Hays]

Axel
What little I've read stated that it was actually 2 pupils rather than a shadow. I don't think that they all have the two pupils. I have never heard what the reason for this is but I think that it is hereditary.

[Axel Hildebrandt]

Lana and Juan, thanks, very interesting regarding the male/female difference and I've never heard of the 2 pupil explanation. I've never gotten very close to one as they tend to be quite skittish around here.

[Declan Troy]

The black pupil extension or dark flecks in the iris is a female characteristic in American Black Oystercatchers. I couldn't connect to the link Juan gave so I'm not sure if this relates to the same research. In the case of Black Oystercatchers sexing based on the eye is pretty reliable (86-96% of the time in a couple of tests). Mis-sexed birds tend to have slight flecking, they tend to be females but can be either sex. Details are in a publication that was in the works last winter but I'm not sure if it is out yet. Details may be different for other oystercatchers but odds are the enlarged pupils/flecks remain a female trait.

[Steve Wheeler]

One has to wonder what the evolutionary advantage is for females developing these flecks. I'm not doubting the work at all... Just wondering why they developed that way? What purpose has it served?

Steve

[James Shadle]

This pretty dang close.
Great question about the OC's eye.
James

[Axel Hildebrandt]

One has to wonder what the evolutionary advantage is for females developing these flecks. I'm not doubting the work at all... Just wondering why they developed that way? What purpose has it served?

Steve

Could it be a 'genetic accident' that doesn't cause any advantage or disadvantage? I think this is how some people explain blue eyes in humans.

Here is the link to the abstract Juan posted, which should work: http://www3.interscience.wiley.com/journal/120088545/abstract

[Steve Wheeler]

Always suspected I was an accident...:eek:

Link works fine.... Interesting paper.... I've never seen one of these birds in person, but would love to someday.

[Mike Milicia]

Can't shed any light on the underlying question here but just thought I'd post a large crop, quick and dirty rendering of an immature Oystercatcher that shows that it apparently takes a while for the eye to develop into the adult version.
Note that the iris is much duller/milkier and the pupil(s) are not very well defined.
This image was made in overcast light with no direct sun, so no shadows here.

[Axel Hildebrandt]

Thanks, Mike! Shadow is definitely out of the question then.

[Fabs Forns]

I've seen the two pupils and seen the clean even eye. Of course, I have no idea of what causes it.

Thanks for bringing up the question and very good images everyone!

[John Chardine]

Can we establish what we are seeing in the eyes of (presumably female) oystercatchers. My reading of the thread and study of the images suggests that we are seeing a perfectly normal, circular pupil with a black pigment spot below and to the front a little, in the yellow iris. Have I got this right?

Yes, excellent topic and like Fabs I have really enjoyed the images. The image of a young oystercatcher posted by Mike is very telling as it shows the black spot developing.