|Mon, 22 Nov 1999 00:31:05 -0700
|email@example.com (Mark Stackhouse)
|The Spanish Fork Gull Mystery (long)
O.K., here it is - the story behind . . .
The Spanish Fork Gull Mystery
First, a little history, so that you can see how this developed on this end.
On October 24, Harold Clayson sent me an e-mail with the first report of this bird. I was able to speak with him that evening about his sighting - he described a gull which was noticeably smaller than the Ring-billed Gulls (RBGU) also present, had a rounder head, and a smaller bill than the RBGU's. These are the "classic," and supposedly most reliable, marks for a Mew Gull (MEGU). At first he thought it was a second-year bird, but after checking other references, he concluded (correctly), that it was a first-year bird. I asked about some plumage characters, such as the tail color, but he was unclear on these. The next day, he reported that bird had been seen by several other observers (including some very experienced birders whose abilities I highly respect), and they had agreed that this was a MEGU. I put it on the birdline that afternoon.
Lesson #1: Don't rely upon only a few features (especially with gulls), even the so-called "best" features, to make your indentification, look at the whole bird.
On the 26th, I had a meeting at Sundance, and took the opportunity to go a little early, and stop by Spanish Fork to look for the gull. It took me almost an hour to pick out the bird from the flocks of RBGU's and California Gulls. One of the problems I had was that I was looking for a bird with the plumage pattern of a first-winter MEGU - that is, a small gull with a mostly dark tail, dark mantle, and thickly marked with dark smudges on the head and belly. I couldn't find such a bird. Finally, I spotted a small gull amongst the RBGU's, which appeared to have a the small bill and round head of a MEGU. But the plumage still wasn't right - from what I could see, this looked more like the Common Gull (COGU) subspecies, not the MEGU subspecies. I called me friend, David Wheeler, and he came down to look at it, and we both agreed that it was a better fit for COGU than MEGU. Unfortunately, the bird was being rather shy while we were there, and we weren't able to get perfect looks at it, and even the photos I took don't show all of the critical features. What turned out to be some irregularities in the tail band looked like broken, worn and incompletely molted feathers (see my Birdnet post of 10/27).
Lesson #2: Don't jump to conclusions (again, especially with gulls) based upon an incomplete viewing of all of the relevant field marks.
That night, I posted a note to the Frontiers of Identification chat-group, asking about the occurrence of COGU in the western part of North America. Several replies indicated that this form was not yet recorded in the west, and that the furthest west record came from central Iowa. This sighting would need a much more thorough review. I posted a brief description of what I had seen, and said that I would get some photos out for review as soon as possible.
Some of the replies proved prophetic. For example:
>From Michael Patton: "In general I think size/shape works fine, but beware of small female Ring-billeds. I've seen a number of them called Mew Gulls in the West, as some have short bills and all females of the large _Larus_ have more rounded heads than do males."
and, from Paul Lehman: "I don't wish to come off sounding too much like a curmudgeon, especially since I am 2000 miles away and haven't even seen the bird, but I can't believe the gull in Spanish Fork is really a Common Gull... Is there no way it isn't "just" a brachyrhynchus [MEGU], or perhaps more likely, a small, runt, small-billed JUVENILE Ring-billed, which occur fairly regularly and get called "Common Gulls" here along the Atlantic Coast about once or twice per year?"
Shortly after this, Colby Neuman brought me his set of prints, which included a number of excellent shots of this bird. I scanned a few of the more useful shots, and, with the help of Weldon Whipple, had them posted on www.utahbirds.org. At the time that I was first scanning the photos, David Wheeler and I spent an evening examining the photos, checking all of our references, and surfing the net for other images of COGU and RBGU. Our doubts regarding the i.d. of this bird grew to the point that we both took it off our lists at that time, and I was mostly convinced that it was a RBGU, but wanted to hear from a few other folks before making a firm judgement on the bird. The problem was that every feature that suggested COGU couldn't eliminate RBGU (they were all within the range of variation for RBGU), and several features were inconsistant for COGU, but good for RBGU. There wasn't much about this bird which supported MEGU.
Here's some of the important comments I got from folks who reviewed the photos on the net:
>From Matt Hiendel: "My feeling is that it is a Ring-billed, not a Common. It is small-billed and the head is that attractive small, round dome, certainly Mew or Common like. But, that is where it stops for me. The gray seems pale, the tail seems too sparse, the wings too dark, and I might see markings on the inner greater coverts, etc. I am not sure of all of this. It is just what it looks like. Then, I go back and look at the bill again, well shown in figure 1. The bill looks on the small end, yet is a bit thicker than I expect on Mew. Common is a bit thicker but this still looks a bit off. So, I think it is a ringie."
>From Bruce Mactavish: "The Utah gull is definitely a Ring-billed Gull. The tail is a give away. The outer three or four tail feathers show a dark shading above the dark tail band. This a sure sign of Ring-billed Gull. Common Gulls have a very clear cut, solid blackish tail band without shading inside of the band. The bold contrast of the clean black tail band with the bright white tail is similar to the impression giving by a 1st winter Franklin's Gull. The tail band is too narrow, especially on the outer rectrices, with a secondary band between the main band and the white tip. This is classic of Ring-billed Gull but wrong for Common Gull.
"The rufous tone to the upper wing coverts is another Ring-billed Gull give away. On a Ring-billed Gull the colour varies from rufous-brown to dark chocolate brown. On a Common Gull the wing coverts are lackluster gray-brown, without a hint of rufous. Photo One shows the shape of the brown marks on the wing coverts as coming to a point which is characteristic of Ring-billed Gull (rounded in Common Gull).
"The bill, though short, is not as proportionately thin as typical Common Gull. Ring-billed Gulls with bills this short are frequent. Base of bill brighter pink than the majority of Common Gulls (dull brownish-pink typical). Common Gulls can have longer bills. The head and neck streaking is more blurred and not as sharply demarcated as the typical Common Gull. There is a sharp contrast between dark brown outer primaries and pale gray inner primaries. On Common Gull this contrast is less stark, somewhere between Ring-billed Gull and 1st winter Herring Gull."
>From Glenn Coady: "Bill is too deep for Mew, greater & lesser secondary covert pattern is typical delawarensis [RBGU] (even though worn & faded), legs look proportionately too long for Mew."
>From Michael Patton:"I think your are correct in concluding that the bird is in fact a Ring-billed Gull.
There are several features that support RBGU to the exclusion of Mew Gull:
1) the tail tip is black with a narrow white band separating it from the black subterminal (MEGU of all subspp. show a solid black area);
2) the lesser and median coverts have a decidedly pointed tip (distinctly rounded on unworn MEGU);
3) dark subterminal area on greater coverts and scapulars (uniform dark on MEGU);
4) heavily spotted hindneck (generally uniform brown or mottled brown on MEGU);
5) tail band too narrow (much wider on all MEGU, esp. _L. c. brachyrhynchus_);
6) sharply contrasting pale area on the inner primaries (generally does not contrast as sharply on MEGU); and
7) paleness of the mantle (darker on MEGU, esp. _L. c. heinei_)."
>From Nick Lethaby: "I took a quick look at the photos and agree with you that it's likely a RBGU. In addition to the comments McTavish made, some of the first-winter scapulars are gray with a dark subterminal crescent. My recollection is that Common Gull does not show this pattern on it's first-winter scapulars where RBGU certainly does."
>From Paul Lehman, Shawneen Finnegan, Tony Leukering: "I am afraid our opinion is unanimous: the bird appears to be a Ring-billed. Every important character we could see either was better for Ring-billed or was "neutral." Here are several of the important points:
1) bill size and shape fine for a smaller Ring-billed, and the color of the base (fleshy-pink) good for R-b but only for some Commons (many, but not all, have grayer-flesh bases)
2) the brown in the wing coverts is a rusty- or orangey-brown, which is good for R-b, but this color in Common (and Mew) is a tan-brown without the dull rusty tones. And very important, many of the internal brownish markings and pale fringes on the covert feathers were pointy or somewhat jagged-shaped, as in Ring-billed, not rounded as in Common/Mew.
3) there are a few small brownish bars or mottling on the base of the tail and uppertail coverts; it is not totally clean white. Having a few markings there is fine for Ring-billed, and is also OK for Common. (Clean white is better for Common, but even the rare Ring-billed can appear to be clean in those areas.)
4) the tail band seems OK for Ring-billed--albeit a bit mangled--and the outermost tail feather clearly has a bit of a band/bar on it; it is not clean white as is typical of Common."
>From Pierre-Andre Crochet (of Uppsala, Sweden):"The greater coverts of the birds are distinctly barred, especially the inner ones. This is another character of RBG as opposed to Common gull.. In CG, the greater coverts are more uniform."
Well, that's about it on this one. This is probably more information than you ever wanted to know about how to i.d. a gull, but, hopefully, we can all learn something from this experience. Just in case you're fealing so discouraged that you're about to give up on gull i.d. altogether, check out this note I received some days after the case had been settled:
>From Dick Newell: "You don't happen to use Stokes Field Guide to Birds - Western Region do you? Because if you look on page 193 under Mew Gull (which I guess should be called Short-billed Gull), the top right picture looks remarkably like your gull. In fact the book is wrong - it's another 1st winter Ring-billed Gull. Anybody using this field guide will be lead astray in this instance - but it's a nice book otherwise."
In fact, I don't even own the Stokes guide, but I checked it out in a shop this morning, and he's absolutely right - the photo is mis-identified. Even the "experts" get it wrong sometimes . . .
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