Skip Russel wrote:
>
> I was looking through my unread Tweeters digests and came across a
> message I couldn't pass up. Hope you're not too sick of this thread
> already....
>
> >>Gene Hunn wrote:
> >>
> >>"Re. light-eyes on Thayer's. It depends on what one means by "light"
> >>perhaps. My impression of ("typical"?) Herring Gull adults is that their
> >>irises are almost white, color of white gold perhaps, really glaring,
> >>while the ground color of Thayer's, and the dominant color when the brown
> >>flecking is minimal is more a rich yellow. Do others agree?"
> >
>
> and Dennis Paulson responded:
>
> >Don't know if I do. I think they overlap. I have a bunch of closeup
> >photos of Herring Gull heads from the Great Lakes (birds that were
> >anesthetized to be banded, weighed, and sexed, also photographed) that show
> >some birds, by the way, with a surprising amount of brown flecking in the
> >iris. They look pale yellow, not white, as--to me--do the palest Thayer's
> >eyes.
>
> I spent a few hours today looking at Thayer's Gull's eyes myself. (I
> think the total number of hours I've logged scrutinizing the iris color
> of gulls is well into the hundreds by now--I don't exactly know what that
> says about me.) Anyway, what I saw today was consistent with what I
> remembered, and that is that there does indeed seem to be a difference,
> in general, between the iris color of Herring and pale-eyed Thayer's.
> First of all, pale-eyed Thayer's are a definite minority among Thayer's.
> Certainly less than 5% of the birds we get on Sauvie Island could be
> defended as being pale-eyed. Of those, the marginal ones look pale-eyed
> only in bright light, while even in dim light, Herring Gulls irides
> always look pale yellow. The majority of the rest have more brown flecks
> than any Herring I've seen around here.

I am sure that this varies from location to location as birds in Vancouver
are different. Here the proportion of pale eyed Thayer's seems to be
as high as 20%, from my observations. One of these days I should go and
try and sample as many as possible and see what I can come up with.
>
> I'm sure Dennis is correct in saying that there is overlap in eye color
> between Herring and Thayer's. He has data to prove it. But I am
> equally sure that this is very uncommon, at least in our part of the
> world. I've seen perhaps two or three Thayer's here ever that had very
> pale yellow, off-white eyes. I think they were as light eyed as any
> Herring Gull's I've seen. (One even lighter.) But whatever population of
> Thayer's it is, (Kumlien's perhaps?) that supplies these birds to us, it
> doesn't do so very often. (I know Dennis and Al will jump all over that
> bit about population. Go ahead, I'm wearing my asbestos suit!) My
> point in all this is that Gene was correct in that there are differences
> in iris color that can be used in the field.

In theory the Thayer's Gulls we see here are the westernmost and therefore
darkest population. These are the "true" thayeri. Therefore, these birds
should all be dark eyed, but obviously they are not.
>
> Since I'm already skating on thin ice, I might as well add that I think
> there might also be a correlation between iris color and bill size in
> Thayer's Gulls. The ones with extremely pale eyes, and again there
> aren't many, almost always (always?) seem to have smaller than average
> bills. As an example, see the one Dennis photographed in _Birds of
> Alaska_. The two or three almost white-eyed Thayer's I referred to above
> had tiny bills hardly larger than a Mew Gull might have. I'll have to go
> back and reread Neal Smith's paper on the evolution of Thayer's/Iceland
> Gulls to see what he had to say about bill size differences. I can't
> recall. (I know some people think Smith's data was cooked, but I think
> his general conclusions may still have a lot of merit.)

This is a really neat observation and it would be interesting to try and
confirm your suspicions. Keep in mind that this may also be due to a sexual
difference, females (which are smaller) are more likely to have pale eyes,
which would be equally interesting as a population difference.
Regarding Neal Smith, I would suggest that you do not read his work as
there is a good deal of data that shows he did not do the white-winged gull
work. It is possible that he did do the Ringed Plover stuff though. Since
this is a pretty nasty thing to acuse someone of, I should give some referen-
ces. Read Snell, R.R. 1989. Status of Larus gulls at Home Bay, Baffin Island.
Colonial Waterbirds 12:12-23.
In this paper several conclusions are given: 1)Kumlien's and Thayers
gulls bred non-assortitavely at Home Bay in 1985. 2) There is no significant
correlation between measures of bill length and an index of primary melanism
3) There is no evidence that the amount of wingtip melanism differs
significantly among three classes of iris melanism (light, medium, dark).
4) He also concludes that the extensive and complicated research protocols
reprted for 1961 by Smith could likely not all have been accomplished
in the time which would have been available, suggesting future workers
view conclusions from those earlier studies cautiously.
Richard was able to match aerial photographs of the area in 1961 with
dates of Ringed Plover specimens Smith collected and was able to see that
it would have been impossible for Smith to have travelled the distances
he said he did, and do his work, given the situation the ice was in at
that time.
>
> By the way, those light-eyed birds I referred to didn't have
> particularly light primary tips. Perhaps primary darkness is not what
> we should be using to differentiate Kumlien's from Thayer's? Maybe they
> really *are* different species and we've just been looking at the wrong
> physical characteristics? (Oh boy, now I'm really in for it!) But
> seriously, is there any hard evidence that there *isn't* assortative
> mating by eye-color among some populations of Thayer's?
>
> One last comment, and then I'll shut up. After Dennis mentioned to me a
> year ago about the brown-flecking in the eyes of Herring Gulls, I was
> fortunate enough to get the opportunity to look through some Herring
> Gull's wintering in Ohio. I'd never been able to see any brown flecking
> in Herring Gull's eyes in all my hours of Northwest gull watching. But,
> lo and behold, a couple of those Great Lakes birds did appear to have
> tiny, fine-grained brown flecks in their eyes. Some of them also seemed
> to have somewhat bigger bills with more noticeable gony angles than do any
> of our Northwest Herring Gulls. I wonder if there are population
> differences that we don't know about in wintering Herring Gulls as well?

I imagine that there are. It appears that most Herring Gulls that breed
on the Great Lakes stay there all year round. Its a completely different,
and probably somewhat isolated population.
>
> Always in rampant speculation,

keep on doing it!
>
> Skip

Al Jaramillo
jaramill at sfu.ca
Vancouver, B.C.
>