BIRDING BY HINDSIGHT: A Second Look at Thayer’s Gull

[Author's Note, April 2018 – Thayer's Gull has now been lumped with Iceland Gull.]

Are you one of those birders whose eyes glaze over when someone starts talking about gull identification? Do you approach the subject of distinguishing immature gulls with awe and fear? If so, this article is not for you.

Are you looking for all the answers to your Thayer’s Gull questions? You’d best look elsewhere, since you’ll find this article will likely raise more questions than it can answer. There will probably be more here about how to misidentify a Thayer’s Gull than how to identify one.

Or, are you one of those experts well versed in the complexities of Thayer’s and Iceland gulls, reading this in search of how to separate the two? Sorry, but I’m neither smart enough nor stupid enough to attempt the impossible.

So, now that no one’s left to read this, it may be safe to proceed. There are certainly lots of birds out there which are difficult to identify, but at least you know why they can be so hard, at least you know there is a field guide or other reference explaining which field marks to look for. The Thayer’s Gull, however, may be unique in that there are more misleading references about it than helpful ones. Indeed, among this gull’s published and alleged field marks, there are probably more misleading marks than there are useful ones.

History

In the first place, consider that ornithologists have long disagreed on just what a Thayer’s Gull (Larus thayeri) really is. Is it a full species, just a subspecies, merely a color morph, should it be lumped or split, and, if so, with what? Consider the convoluted chronology of L. thayeri:

1) Initially, it is a full species.

2) Later, it is a subspecies, lumped with Herring Gull (L. argentatus).

3) Still later, based on research on Thayer’s and Iceland (L. glaucoides) gulls, it is split from Herring Gull and recognized as a full species, and considered still split from the darker Kumlien’s race of Iceland Gull (L. g. kumlieni).

4) Subsequently, the validity of this Thayer’s Gull research is widely discredited.

5) Consequently, though the American Ornithologists’ Union (AOU) continues at present to recognize Herring, Thayer’s, and Iceland gulls as three distinct species, many ornithologists now consider the Thayer’s lumped with Iceland Gull as one of three subspecies. That is, the darkest gulls breeding in north central Canada would be the Thayer’s subspecies (Larus glaucoides thayeri), the whitest gulls breeding in Greenland would remain as the nominate Iceland subspecies (L. g. glaucoides), and the in-between gulls breeding in northeast Canada would be the Kumlien’s subspecies (L. g. kumlieni).

6) Yet another current theory holds that Thayer’s should be lumped with Iceland, but that there are no subspecies involved. That is, the transition from darker to in-between to whiter Iceland Gulls is gradual or possibly random, that it does not necessarily involve geographic ranges or subspecies. That is, these darker and whiter gulls may only be color morphs, just like there are among Snow Geese and Gyrfalcons.

7) Doesn’t anyone out there want to advance the Thayer’s = Herring X Iceland hybrid theory?

References

If ornithologists cannot agree on what a Thayer’s Gull is in the first place, how can you be expected to know what it looks like? But the Thayer’s Gull can’t entirely be ignored since it is indeed out there and can be correctly identified. It is even classified as a Regular Minnesota species, with several reliable records per year, mostly in fall and winter around Lake Superior and in the Twin Cities.

So, you’re going to have to consult your library. First, as far as the field guides go, they don’t go far enough. If you have a Peterson, Golden, Stokes, Griggs, or Kaufman field guide, just leave it on the shelf. Their treatments of this complex ID are incomplete and consequently more misleading than helpful. The Geographic field guide is better, but even this excellent guide falls somewhat short. The Sibley guide’s many illustrations, though, are a better place to start. And be sure to study more than just its 13 Thayer’s Gull pictures: the full page on Iceland Gull and the two full pages on Herring Gull are of equal importance.

Next, you’ll need to do some reading in some additional sources. Still in print is Kenn Kaufman’s Field Guide to Advanced Birding, which has a very helpful Thayer’s Gull chapter written by Kevin Zimmer. There is probably no better single reference on this subject. I also recommend the article “Shades of Gray: The Catch 22 of Thayer’s Gull?” by Steve Howell, which appeared in the December 1998 of Birders Journal (7:305–309). This short and readable article may not explain Thayer’s Gull ID, but it does clearly discuss what the problem is and how to approach it.

As some experienced birders are aware, there are several other well-known, widely read, and “standard” references on Thayer’s Gulls identification. What about these? Well, here they are, but exercise caution: some of them are not the solution but part of the problem! In chronological order....

1966: The now widely discredited research which considered Thayer’s Gull as distinct from both Herring and Iceland gulls is published as an AOU monograph. Many ornithologists are of the opinion that much of the field research was simply fabricated.

1973: The AOU publishes its check-list supplement in the Auk (90:411–119), which concurs with the 1966 research on Thayer’s Gull as a distinct species. Few present-day ornithologists agree with this treatment, however.

1975: What is probably the first widely read article on Thayer’s Gull ID is published (American Birds 29:1059–1066). This early article admirably urges caution when making an identification, but it also discusses and reaches some premature ID conclusions within the context of Thayer’s as a separate species. Additionally, the article includes some misleading photos, especially those of the folded primaries on some specimens and the photo on the magazine cover (December 1975). This latter (under-exposed?) photo shows an adult Thayer’s with a dark gray mantle and deep pink legs and feet, and to this day many are under the misconception that adult Thayer’s are supposed to have darker gray mantles and deeper pink legs/feet than Herrings and Icelands.

1980: The December issue of Birding prints that journal’s first Thayer’s Gull ID article (12:198–210). The text is accurate and well-written, but it is handicapped by its illustrations. The five color photos are good (especially the first-winter bird on the magazine cover), but the color plate showing three immature plumages is not entirely accurate, and the black-and-white photos are either too small or too dark to be as useful as they should be.

1982: The first edition of Grant’s Gulls: A Guide to Identification is published....but with no mention of Thayer’s Gull! This classic and definitive guide was written from the European point of view, and the Thayer’s Gull had apparently not yet been recorded in Europe.

1986: The second edition of Grant does include Thayer’s Gull, but it (and other North America-only species) receives only limited treatment. There are only seven photos, and five of these fail to show any useful field marks. European birders, no matter how expert, probably have limited Thayer’s Gull experience at best. Equally as important, Iceland and Herring gulls in Europe are of different subspecies than those here, so any Thayer’s Gull comparison with these two similar species from such a European perspective may not be entirely useful to us.

1991: The October issue of Birding publishes a long article on Kumlien’s-type Iceland Gulls (23:254–269). Since Thayer’s and Iceland gulls are really the same thing, after all, this article with its numerous color photos is certainly worthwhile. The caveat is that at least seven of these photos, all labeled as Icelands, show birds which could easily pass for Thayer’s Gulls. Some of the captions admit these birds could be some sort of Thayer’s Gull integrades, but there is no explanation as to what they really are and why.

1998: Another highly regarded and oft-quoted article on Thayer’s Gull ID is published in the British journal Birding World (11:94–101). However, as mentioned above with the Grant guide, the value of this European article to North American birders may be limited.

2003?: Another comprehensive guide to gulls is said to be scheduled for publication in January. Gulls of Europe, Asia, and North America by Olsen and Larsson sounds like it will far surpass Grant as the definitive guide with its 544 pages, 93 color plates, and 800 color photos. Note, however, it is written from a European perspective.

[Author's Note, August 2016 – In 2007, a very useful and recommended guide from an American perspective was published: Gulls of the Americas by Howell and Dunn.]

How to Identify a Thayer’s Gull

Well, if you’ve made it this far, I assume you already know — or at least know where to find — the basics of Thayer’s Gull ID. To begin with, before listing some field marks, here are some ground rules to consider:

• Thayer’s Gulls at any age are quite variable in overall plumage. Some are as dark as a Herring Gull; others are as pale as an Iceland.

• For the time being, don’t worry about separating those paler Thayer’s Gulls from an Iceland. No one knows how to do it consistently because, as anyone with common sense knows, a Thayer’s already is an Iceland! The more important issue is telling a Thayer’s from a Herring Gull.

• For now, don’t worry about things like Glaucous-winged Gulls, Glaucous-winged x Herring gulls, and other hybrids. Though any of these can bear a strong resemblance to a Thayer’s Gull and present a serious ID problem, their infrequent or unlikely occurrence in Minnesota puts them beyond the scope of this introductory article.

• Before identifying a Thayer’s Gull (or any other difficult gull), decide on its age. A mostly brownish gull, perhaps with some gray on the back, is less than two years old: i.e., a juvenile, 1st-winter, or 2nd-winter bird. The field marks to consider on these gulls are mostly different than those to examine on a gull which looks like an adult or close to it: i.e., it’s more than two years old and in 3rd-winter, 4th-winter, or full adult plumage.

• The identification points below will only briefly cover the “field guide” basics, and there is no need to elaborate here on what your Sibley or Geographic pictures already show. And, for a more comprehensive analysis, that’s what that whole bunch of references above is for.

• Don’t assume every gull you see can be identified: Thayer’s Gull ID is tough. Be prepared to leave some gulls as unidentified; or, if you insist on trying to identify them all, be prepared to make lots of mistakes.

• Finally, after you’re satisfied that the field marks you’re seeing look good for a Thayer’s Gull, read the “How to Misidentify” section. Unless you do so, unless you are aware of the various caveats involved in this ID problem, a misidentification may well result.

So, here are some field marks on a 1st-winter type gull which should prompt you to take a second look, especially when compared to nearby Herring Gulls of the same age. Be sure to note, however, none of these marks alone is diagnostic, and all are qualified in the “Misidentify” section:

• The paler brown and whitish-edged upper surface of the outer primaries, visible on both standing and flying gulls.

• The paler upper surface of the tail, often with a solid brownish or grayish sub-terminal band.

• In flight, the paler or whitish under surface of the flight feathers.

• The usually smaller bill, head, neck, and overall size; similarly, the usually rounder and less-flat crown profile.

And, here are the field marks on an adult or sub-adult which should prompt you to take another look at the gull to see if it’s a Thayer’s. Again, you’ll find all but one of these marks subject to qualification in the “Misidentify” section:

• As with 1st-winter types, the usually smaller bill, head, neck, overall size, and rounder head.

• In flight, the mostly white under side of the outer primaries with only a narrow black trailing edge. This feature is also often visible on a standing gull when the under side of the opposite folded wing tip is showing.

• The upper surface of the outer primaries with less black and more white than on an adult Herring Gull. Note this is mostly visible when the primaries are spread in flight; the folded primaries on a standing adult Thayer’s may look like a Herring’s.

• The usually brown eye (i.e., iris) color.

• At very close range, a purple or reddish orbital ring; a Herring Gull’s ring is yellow. (An orbital ring is a narrow, unfeathered ring around the eye and is hard to see.)

How to Misidentify a Thayer’s Gull

Now comes the easy part. After all, lots of birders already misidentify Thayer’s Gulls. Or, more accurately, they mistake other gulls as Thayer’s. As mentioned earlier, trying to identify a gull as a Thayer’s without being aware of the points covered in this section will often result in an error.

Among the field marks of Thayer’s and similar gulls at any age which are not really field marks, or only work some of the time, and/or are frequently misunderstood:

• On the average, a Thayer’s Gull has a smaller bill, a smaller head and rounder crown, a thinner neck, and smaller overall body size than a Herring Gull. (Similarly, an Iceland averages smaller than a Thayer’s.) However, a male gull can look larger than a female of the same species, and it is not unusual to see a Thayer’s looking just as big as a Herring (or an Iceland just as big as a Thayer’s). Use size and shape with caution, or not at all, and be aware there is overlap between species.

• When trying to judge how dark or light the primaries are on a suspected Thayer’s Gull, be prepared for the folded primaries of a standing gull to look darker than when these primaries are spread in flight.

• When trying to judge how dark or light any part of a gull is the field, you need to take into account what the light conditions are, and at what angle you are viewing the gull. (Gulls at an angle can look darker than those fully perpendicular to your position.) And when looking at a gull photo, be aware that variations in film type, camera exposure, film processing, or how well a magazine or website reproduces a photo can all easily lead to misconceptions of what the gull really looked like.

Similarly, these field marks of 1st-winter type gulls need to be qualified and should be only used with caution or not at all:

• Lesson number one involves what is probably the most common mistake made with trying to identify an immature gull as a Thayer’s. In spring and summer, the plumages of many Herring Gulls (and other species) are typically worn and faded. Consequently, their primaries, tail feathers, and overall plumage appear quite pale — even whitish. Some are even paler than the worn 1st-summer bird illustrated in Sibley. The result: even experienced birders often mistakenly report these as Thayer’s Gulls.

• The bill color, eye color, and leg/foot color of a suspected Thayer’s Gull are no different from a Herring Gull of the same age. It is worth noting them in your field notes and sketches, but none are diagnostic field marks for these immatures.

• Some birders are under the impression that an area of darker feathers around the eye is a diagnostic mark of a 1st-winter Thayer’s. Not so: Herrings and Icelands can look the same way.

• Beware of the folded primaries of some 1st-winter Herring Gulls which are narrowly edged with white and can suggest those of a Thayer’s.

• On the average, a Thayer’s overall plumage looks “smoother” or more cleanly and neatly marked than on a Herring Gull. However, juvenile Herrings not yet attaining 1st-winter plumage can look just as smooth and neat as a Thayer’s overall.

• The under side of a flying Herring Gull’s flight feathers often can look as unmarked and as pale as a Thayer’s. When looking at a suspected 1st-winter Thayer’s in flight, it is better to examine the upper wing surface. (On adults, the under side of the primaries is more helpful.)

• Speaking of the upper wing surface, the Thayer’s has a “dark-light-dark” pattern on the flight feathers: i.e., outer primaries and secondaries darker than the paler inner primaries. While this is often a good mark to separate a 1st-winter Thayer’s from an Iceland, it does not work to distinguish a Thayer’s from a Herring Gull – Herrings have this same pattern.

• Finally, for those still trying to distinguish a Thayer’s from an Iceland Gull, beware of two marks of dubious merit you may have read about. One is the tertials pattern: solid-colored = Thayer’s; speckled = Iceland. The problem is I have seen gulls which in every respect looked like a normal 1st-winter Thayer’s — except for their speckled tertials. And some references have indicated that dark spots near the tips of the primaries are diagnostic of 1st-winter Icelands. Hardly: many Icelands lack them, and many Thayer’s have them.

Finally, these field marks of adult and near-adult gulls could certainly use some further explanation:

• Lesson number one involves what is probably the most common mistake made with trying to ID an adult gull as a Thayer’s. In late summer and fall, adult Herring and Ring-billed gulls are in molt, which results in a reduced amount of black being visible in their wing tips. At some angles, some flying birds can almost look mostly or entirely “white-winged” — just like a Thayer’s Gull, or even a Glaucous or Iceland.

• Use special caution before calling any brown-eyed gull a Thayer’s. For one thing, you need to make sure the gull is really a full adult in the first place. Third-winter Herring Gulls, for example, generally resemble full adults, and many of these have dark eyes. (I also suspect some 4th-winter Herring Gulls, which are essentially adults, can even have dark eyes.) For another thing, at a distance or in poor light a yellow-eyed gull of any species can appear to be dark-eyed — and consequently be mistaken for a Thayer’s. (Or for a California or Mew gull, for that matter.)

• And even if that gull is really a full adult and the iris is really dark, remember that some Thayer’s (reportedly 10% of them) have yellow eyes. And I have had close looks at a few full adult Thayer’s Gulls over the years which had one yellow iris and one brown iris! Or were these Herring Gulls?

• It has been said in some references that adult Thayer’s Gulls have a darker gray mantle and deeper pink legs than Herrings. I doubt this is true at all regarding mantle color, any leg color difference may hold only some of the time, and I wouldn’t rely on either feature as a consistent or diagnostic field mark.

• Finally and unfortunately, as illustrated in Sibley and as I have seen on a few occasions, an adult Herring Gull rarely can have only a limited amount of black on the under side of its outer primaries. Such birds could therefore be easily mistaken for Thayer’s.

Conclusions?

Well, perhaps there aren’t any! Thayer’s Gull taxonomy is still a work in progress, the perfect Thayer’s Gull identification reference has yet to be written, and almost all Thayer’s Gull field marks involve a caveat or two. But, again, there are Thayer’s Gulls migrating through and wintering in Minnesota, and some of them can even be identified.