Record # 7-1998
Possible Yellow-footed Gull
Additional Materials -- E-mails, notes, opinions

E-mail from Keith Evans to Steve Hedges

Date: Wed, 20 Oct 1999 19:40:28 EDT
Subject: Re: Yellow-footed Gull

After Mark Stackhouse and I had some discussion abut Yellow-footed Gull vs Lesser Balck backed Gull identification. I went back and located all 19 photos that I took. – some are blurry. But still show certain characteristics. I had originally sent three photos to the Records Committee, two of the single bird, one standing on the bank and one swimming, and one of the Yellow-footed with a California Gull for size comparison.
After determining that there might be some confusion with a Lesser Black-backed Gull, I looked for a couple of other characteristics. A couple of my slides show the length of the wing extension beyond the tail -- the wings don't extend near as much as they would on a Lesser Black-backed.
Second, in one slide I have a California eating the same fish, and in the same feeding pose, as a slide of the Yellow-footed. Using the fish as a "constant," I measured each fish:gull ratio with calipers on the original slide. Assigning a value of 20 inches Lo the California, the Yellow-footed would be 27.4 inches. Assigning a value of 23 inches to the California, the Yellow-footed would be 31.5 inches long (this is not exact as to the way field guides measure length as I went to the end of the wing extension instead of the tail). However, this does tell me that the California Gull was only 73% as big as the Yellow-footed – I believe that makes the Yellow-footed too big for a Lesser black-backed.
I hope this helps, if you need more, let me know. Keith

Email from Michael A. Patten to Keith Evans
(Prefaced by an e-mail from Keith Evans to Mark Stackhouse and Steve Hedges)

Date: Wed, 29 Sep 1999 18:16:20 EDT
Subject: Fwd: Yellow-footed Gull
To: westwings@sisna, com,

I was asked by a Michael Patten, Univ. of Calif., for photos of the Yellow-footed Gull I reported from Bear River Refuge last Oct. Dr, Patten believes it was a Lesser Black-backed Gull -- see lengthy details in enclosed letter.. [personal comments excluded]... Thanks Keith

*** Email from s Michael A. Patten***

From: "Michael A. Patten" <>
Subject: Re: Yellow-footed Gull
Dear Keith,

As promised, I showed the gull photographs to a bunch of friends this weekend to get their objective opinions. I did not tell any of them the date, location, or circumstances in advance, to ensure that they would not be biased in their response. I also instructed each of them to make only one choice, and some were more firm in their choices than others. As you can see from the opinions listed below, in only one case did someone suggest a Yellow-footed Gull, and he was fairly tentative.

Person - Opinion
N. Bruce Broadbooks - Yellow-legged Gull (tentative)
Jon L. Dunn - Lesser Black-backed Gull
Matthew T. Heindel - Lesser Black-backed Gull
Andrew Howe - Yellow-legged Gull (tentative)
Vernon Howe - Lesser Black-backed Gull (tentative)
Guy McCaskie - Lesser Black-backed Gull
Joseph Morlan - Lesser Black-backed Gull (tentative)
Gary H. Rosenberg - Yellow-footed Gull (tentative)
Scott B. Terrill - Heuglin's Gull (tentative)
John C. Wilson - Lesser Black-backed Gull (tentative)

I polled another =Bll0 people, none of whom were certain enough (or brave enough!) to have an opinion on the bird. This poll was obviously informal, so you shouldn't quote any of the above opinions in print without getting permission from that person.

In any event, despite the variation in opinions, I think it is clear that the bird is not a Yellow-footed Gull. Indeed, if I may offer my own subjective assessment of the knowledge/skill levels of the various people I polled, Dunn, Heindel, McCaskie, and Morlan are amongst the best and most knowledgeable birders I have ever met. All stated that they felt the bird was a Lesser Black-backed Gull (though Morlan was a bit tentative). Rosenberg and Terrill are also extremely good and extremely knowledgeable, and both quickly conceded that the bird best fit a Lesser Black-backed once I made my announcement (and expressed my own opinion) at the end of my poll. Between Dunn, Heindel, McCaskie, and myself, we have collectively seen thousands of both Lesser Black-backed and Yellow-footed gulls (and I wrote the Birds of North America account for the latter).

I have already given you some of the reasons why I believe the bird was a Lesser Black-backed Gull. Below I outline those reasons again to ensure that you are comfortable with them, and I present a more detailed analysis of them.

(1) Orbital color. Both the Western and Yellow-footed gulls have yellow to orange-yellow (sometimes orange in high breeding) orbital rings. I am unaware of either species ever showing a red orbital. Indeed, a red orbital narrows the field of potential dark-mantled species to a) Lesser
Black-backed Gull, b) Slaty-backed Gull, c) Heuglin's Gull, d) Yellow-legged Gull. The mantle is too dark for any subspecies of Yellow-legged Gull, including Larus cacchinans michahellis and L, c. mongolicus, the two most likely vagrants to North America (only the unlikely L. c. atlantis has supposedly been recorded).

(2) Leg/foot color. The evenly colored, rich straw-yellow legs and feet are entirely consistent with a Lesser Black-backed Gull. The Slaty-backed Gull never shows anything other than pink legs and feet. The coloration is too bright for most Kelp Gulls, particularly in Basic plumage, and is too yellow for a Heuglin's Gull of the central Siberian subspecies L. heuglini taimyrensis, the only subspecies likely to reach North America (it is as yet unrecorded) given that it winters in southeastern Asia and regularly reaches Japan. The Yellow-footed Gull almost always has a pink/orange tinge to the legs, such that they contrast with the feet: and neither the legs nor the feet are pure straw-yellow.

(3) Head streaking, Amongst the large, dark-mantled gulls, the Western, Yellow-footed, and Kelp gulls tend to lack head streaking in winter. Some Westerns, particularly of the nominate (northern) subspecies, acquire a dull gray hood in winter, but none look streaked. The amount of streaking on the head of an adult Basic Yellow-footed or Kelp in minimal indeed. Of the yellow-legged species, distinct head streaking is present on Basic Lesser Black-backed, Yellow-legged, and Heuglin's gulls.

(4) Mantle coloration. I am amazed at the range of variation in mantle color shown in the three photographs. Still, I assume the two closer photos show the truer mantle color (i.e., dark gray, contrasting distinctly with the black primaries). The Yellow-footed Gull generally has a darker mantle than what is shown. Indeed, to my eye the mantle color looks perfect for a L. fuscus graellsii Lesser Black-backed Gull, the subspecies that accounts for 99% of the North American records of this species.

(5) Iris color. Although the Yellow-footed Gull does have dull gray-yellow eyes when adult, this species does not show the distinct "staring" (clear) yellow eyes of a Lesser Black-backed Gull (which is essentially the same as on a Herring Gull). The eye color of your bird is a great fit for a Lesser Black-backed, but lies outside the range of variation in my experience.

(6) Head/bill shape. One of your photos shows the bill as being quite heavy, but it still lacks the distinct bulbous tip and extremely heavy appearance of a Yellow-footed Gull bill. Also, the head shape, with the more rounded profile and steeper forehead (and relatively large eyes), does not fit a Yellow-footed/Western, which tend to have angular foreheads and flat crown (and relatively small eyes).

(7) Primary spot. The field identification of Heuglin's vs. Lesser Black-backed gull is still being explored, but one of the best means of distinguishing them is the large, wide white mirror on pl0 (the outermost primary). I can see an extensive white mirror in one of your photos, and you noted this mark in your description as well, so it too points to a Lesser Black-backed. Note that this species may or may not show a small mirror on p9 (I cannot see p9 in any of the photos).

(8) Gonydeal spot. A classic mark of an adult Lesser Black-backed Gull is that the red spot on the gonys (the angled part of the lower edge of the bill) is elongated or ellipsoid, not mostly circular like it is on other large Larus. Your bird has a distinctly elongated red spot on the gonys.

(9) Wing length. The Lesser Black-backed Gull is a long-winged bird, making it look rather sleek compared to a Herring or other large Larus (though it is not too different from a California Gull). Your bird does not look particularly long winged to me, but note that all large Larus exhibit strong sexual dimorphism is size, with males being consistently larger, with heavier bills, more angular heads, and shorter wings.

In closing, between the orbital color, eye color, head streaking, leg/foot color, mantle shade, gonydeal spot, and the extent of the white mirror on pl0, I feel that your bird can confidently be called an L. f. graellsii Lesser Black-backed Gull. Given the wing length and bill size, it was
undoubtedly a male.

I hope that you find this information interesting and useful. As I stated previously, it is a significant record regardless, so I am thrilled that you are writing a paper about it for Utah Birds. Also, please feel free to quote me as much as you wish, or to share any portion of this letter or my previous ones with other interested parties, including the Utah Bird Records Committee.

Thanks a million for the opportunity to review this record. Please do not hesitate to contact me if you have any questions or comments.


Michael A. Patten
Department of Biology
University of California
Riverside, California 92521


Email from Mark Stackhouse to Keith Evans

*** e-mail from Keith Evans to Steve Hedges ***

Date: Sun, 3 Oct 1999 20:28:24 EDT
Subject: Fwd: Yellow-footed Gull
To: shedges@mail.netutah, com

Steve -- here are the notes that Mark sent me about the YFGU. makes some very good points, Keith

*** Email from Mark Stackhouse to Keith Evans (included in the above e-mail) ***

Note: When this e-mail was originally printed, there were some letters missing from the ends of some of the lines along the right margin of the printed page. After scanning this pages and changing them into text files, I’ve added the obvious missing lettering and if there were three or more and not as obvious, I put the addition in brackets. (Example: wh[ich])  ~ M. G. Moody

Date: Thu, 30 Sep 1999 23:14'33 -0600
From: westwings~sisna,com (Mark Stackhouse)
Subject: Re: Yellow-footed Gull
Cc: "David S. Wheeler" <>


I'm less impressed the more I look into this issue. I'm sure they're very experienced, but I'm having trouble finding documentation or examples to support the analysis from Michael Patton. In the cases where the features he describes check out with the photos and references I've checked, I disagree that the bird you photographed is more like a LBBG than YFGU. By the way, the photos of the Lake Powell bird can be viewed on th web at:


If anything, according to the analysis of the "California Group this bird is even less like a YFGU than the bird you photographed.

Here's my read on the items raised by Michael:

(1) Orbital color. I've found references for the orbital color YFGU as yellow, and red for LBBG. The orbital color of the bird in your photo appears to be reddish, but it's not terribly clear. I've looked two photos of YFGU (one from Texas, the other from Salton Sea) which show a detail of the eye, and the orbital ring on both appears red - e[ven] redder than in your photo, Go figure. Maybe this is easily distorted in photos.

(2) Leg/foot color. I think the "straw yellow" color refered to in your photo is, as you suggest, distorted in that photo. The photo wh[ich] shows the legs and feet appears to be over-exposed, probably due to the light background of the water and mud contrasting so sharply with the dark vegetation. Anyway, I don't think the legs and feet look to be uniform color as Michael apparently judges. The feet look to be brighter than the legs to me. I had trouble seeing this difference in many of the photos I saw, and couldn't find any reference to it in the literature.

(3) Head streaking. He's right that the YFGU, like WEGU, shoudl not have much head streaking in winter (although I've seen a few WEGU wi some streaking on the face), but the LBBG has LOTS of streaking especially on the nape and back of the neck. I think that the streaking on your bird is much closer to a YFGU or WEGU, and not at all like LBBG.

(4) Mantle coloration. Again, I disagree with Michael on the assessment of mantle color. I think that the closer photo is a bit over-exposed giving the mantle a lighter-than-true appearance (as your notes suggest. In any case, the mantle color is much darker than any of the photos of the L. fuscus graellsii LBBG, and very similar to most of the YFGU photos I've examined, and the few I've seen. It also appears darker than the LBBG's I've seen. Note that the mantle of the "Lake Powell bird" is no as dark as yours.

(5) Iris color. In the photos/references I've examined, I can't find anything here which could, from your photos, be distinguishing between LBBG and YFGU. The iris color of both appears to be too similar to t[hose] from your photos (and maybe anyone's - I've looked for this difference in dozens of photos of both species, and can't see it).

(6) Head/bill shape. I agree with Michael's description of the differences in head and bill shape between LBBG and YFGU, and the eye-size appearance, but can't imagine why he thinks that the bird in your photo is better fit for LBBG than YFGU. According to these features, your bird look precisely like YFGU, and not at all like LBBG. While the bill may not be [as] heavy as some YFGU's, it's much too heavy for any LBBG I can find. The gonydeal angle is too prominant and too close to the tip of the bill for LBBG, and the slope of the culmen is much too steep. The bill is also too wide, measuring 5x the eye (perfect for YFGU) and not 4x (appropriate for LBBG).
The head shape is also perfect for YFGU, and not at all like LBZ In the one photo which shows the bird to be round-headed, steep-foreheaded, the head is obviously angled towards the viewer, distorting the head shape (and bill shape). The close photo shows the profile and bill shape beautifully (these can't be over-exposed), The bird is heavy-billed and flat-crowned, with an angled forehead and a small eye. I can't find a single LBBG gull photo which matches your bird on these features, Note that the "Lake Powell bird" looks even less like a "classic" YFGU than your bird.

(7) Primary spot. The white mirror on pl0 is essentially similar on both LBBG and YFGU, so there's no help here. I did find a reference which discribed the white apical primary spots on the folded wing for both YFGU and LBBG. On LBBG all of the spots are smaller than the eye, and on YFGU, the first spots are larger than the eye, with the last two being smaller.
Although it's difficult to see this clearly in any of your photos the one photo does show the last two a-spots are clearly smaller than the others.

(8) Gonydeal spot. Yes, your bird does have an elongated gonydeal spot, but I have seen many photos of YFGU which have a gonydeal spot similar to yours. I don't know how reliable this feature is - it seems like the kind of feature which can show lots of variability.

(9) Wing length. The wing length of your bird (as can best be determined) supports YFGU, not LBBG.

(10) Size (this is my own). Your bird is clearly larger than the CAGU in the same photo, a relationship which you noted in your description. The size relationship appears to me to suggest a bird as large or larger than a HEGU. A LBBG would be about the same size as CAGU, and clearly smaller than a HEGU. There is no way that this bird is a LBBG, based upon si alone.

In conclusion, based upon a more detailed analysis of the issue and your photos, I'm keeping it as a YFGU on my records, and on my checklist of Utah birds (unlike the "Iceland Gull," which I dropped after a similar review). I simply don't agree with the analysis of Michael or the others whom he showed the photos. Maybe the "unbiased" method of "don't know where they're taken," and "don't have any written description," for identifying photos is not the best way to get a correct i.d. After a fairly extensive review (your note really bothered me), if I were on the Utah Records Committee, I would vote Yellow-footed Gull.

I also saw a Herring Gull at BRMBR last week, so I think you’re right about the winter gull season starting. Is it a bad omen to be beginning another new season without having resolved a controversy from the last? :-)

Good birding!

Mark Stackhouse
Westwings, Inc.
1432 Downington Ave.
Salt Lake City, UT 84105
(801) 487-9453